Fruit And Nut Trees From Seed
Introduction
This page provides a few tips for
growing a variety of edible perennial plants, fruit
and nut trees and bushes from seed, especially tropical, subtropical
and arid climate species started indoors for maximum growth rate for
later planting out. There is a lot of genetic variability in
seeds so general statements are only
as guidelines.
Characteristics,
including fruit taste, often vary widely across individuals of a
species. Some species
exhibit more consistently desirable characteristics among individual
plants
so that little selection is
needed for improvement. Some varieties have been selected so that
seed propagation consistently yields desirable characteristics.
Other varieties have
been selected for desirable characteristics but do not replicate these
in seed propagation so depend on clonal
propagation for
their replication. Commercial growers often graft an optimum
fruiting variety onto an optimum rootstock variety. If you grow a
seedling
and are not satisfied
with its fruit, you may be able to graft something else onto
it.
Advantages of seed propagation include the availability of seed, a
simpler propagation procedure, and genetic
variability for developing new cultivars. Advantage of clonal
propagation include exact replication of selected characteristics that
may (or may not) suit your requirements, easier culture given
documentation, and in many cases a shorter juvenile period.
Selection
Strategy
If you want to end up with one healthy seedling, try germinating a
dozen
seed. Expect only a few to germinate and some to be
defective. Of course there is great variety in germination rate
among species and seed sources. Select the most vigorous one, or
even better, grow three healthy seedlings to end up with one
healthy
adult tree. But it's very likely that more trees are desirable
for selection of a superior producer, and also for pollination.
Isolated individuals of some species, or select cultivars,
can self-pollinate and produce
abundantly. But all species exhibit various types and degrees of
self-incompatibility and most require the genetic
variance of two or more non-cloned trees for
good fruit set. Many species have perfect flowers but produce
better with cross-pollination. Seedlings of these species may be
planted in pairs to help ensure
good fruit set. Some species produce male and
female flowers on separate trees without a hint of a tree's sex until
it flowers. Other species, like avocado, produce two types with
different reproductive timing. Seedlings of
these species may be planted in threes to ensure
good fruit set. Other species produce male, female, and some bisexual
trees that can
pollinate themselves and other
females. Seedlings of these species may also be planted in threes
but in the case of papaya, five may be planted to provide a great
chance of having one female tree which is preferred because they flower
and fruit continuously and their fruit can be seedless when the garden
has exclusively female trees.
If space is limited, multiple seedlings may be planted in
one hole, or in some cases pollinator scions may be grafted onto
receptor trees. Some species have wide variance in fruit quality
such that planting extra seedlings offers a better chance of one
seedling producing high quality
fruit. This is especially important if
you want to market your excess production. For species not
well-adapted to the climate, a large number of seedlings may have to be
planted to net just a few productive individuals. Plant the
seedlings in a group and remove your least favorites as they
grow
large and compete for resources.
Obtaining
Seed
Seed viability periods vary with species. Generally, fresh seed
germinates readily, and older seed much more slowly and
unreliably. Expect poor
or inconsistent germination rates in bought
seed unless you can be sure that the seed is fresh. I found all
shelled
nuts sold for food non-viable, probably due to
heat-sterilization. Fresh
fruit/nuts in supermarkets tend to readily germinate. Ethnic
grocers extend the variety of available fresh produce. Farmers'
markets,
country produce stands, u-pick orchards, horticulture clubs, neighbors
willing to share, or on the ground under their trees, and the wilds are
all
places to
find fresh fruit/nuts with viable seed. A mix of seed from
different parent trees from different locations for genetic diversity
is good. The parent trees should be healthy, and if from wild
stands should be from the perimeters where the climate resembles where
the seedling will be planted. Seed-borne pathogens
might be killed by exposing the seed to direct sunlight for 10 to 20 minutes.
Keep some non-treated seed for backup.
Germination
Perennials generally take longer to germinate than annuals so
don't use the germination time for wheat sprouts as your
standard. The optimum germination conditions vary widely between
species,
but all need a certain level of warmth, moisture and time. Most
seed germinate
much faster when planted immediately after extraction from ripe
fruit. The riper the better usually. Seeds that float in
water are usually not viable. If they don't germinate
rapidly, allow them to completely dry out, then try again. Some
species' encoded survival strategy involves a
randomness in germination time spanning months. Some species
habituated to cold climate require a minimum period of
cold
and damp which may be created by containing the seed in a damp medium,
e.g. sand, in a plastic bag in the refrigerator. Species vary but
generally a 70 to 80 degree F
germinating medium is necessary. Bottom heat may be necessary.
For the medium itself I've used sand but it has to be re-wetted
frequently. Covering the container with plastic to maintain
moisture invites fungi.
Laying wetted tissue paper over the surface
can slow the rate of evaporation. The medium should be
sterilized by boiling in a pot with
water for 3/4 hour. Some seed should be buried to a
depth 2
or 3 times their size to hold the seed coat secure while the stalk
pulls
itself out. I've had real problems with guavas, cherimoyas and
others failing to shed the seed coat. The other reason to bury is
moisture regulation.
I haven't had a lot of success sprouting seeds in water but avocado did
fine, and a few pistachios did. Many species seem to
respond better when the medium is allowed to dry significantly between
waterings.
Seed orientation is fairly important to avoid crooks and twists.
Generally the tip where the
root and stalk emerge should be placed horizontally so that each
can grow in its preferred direction with equal ease. Seed tips
are generally
identifiable as the pointed end of the shell or embryo. Split
shells
like walnut should be planted so the shell hinges open sideways.
Same for split
embryos. For many seeds,
including tamarind, cherimoya and black sapote,
the stalk emerges while the bud is still in the buried seed coat, and
it forms a 180 degree bend for leverage to pull the
bud out. Carob doesn't do the 180 degree bend and may be planted
tip down because its seed coat
readily
splits away from the emerged bud. The mango embryo should be
planted with the two ends horizontally opposed, edge vertical, with the
"garbled" long edge down. Avocado is
planted with the eye or flat end down. Date palms sprout straight
regardless of seed orientation.
Germination is generally faster in species with woody shells when the
embryo
is removed. I removed the mango shell with wire snippers, very
carefully cutting around half way and pulling the remainder
apart. Canistel shells crack apart quite easily. Capulin
cherry shells are easily split with a pair of
pliers. It appears unnecessary to remove the walnut shell as the
shell easily opens like a clam when moist and germination seems to be
better in-shell. Seeds from commercial jujube are
usually missing
the embryo from a lack of genetic variance in the pollen. I tried
numerous different seed sources and found very few embryos and even
fewer that would sprout. I finally had success with a couple of
bags of particularly delicious dried fruit - two pounds of fruit
yielded four sprouting embryos. But three of the four had major
problems pulling out of their seed coats and raising their cotyledons
above the soil.
During germination, light is less important for most species but air
circulation is important to
prevent fungus on the growing medium surface. After the
sprout
breaks, full light and good air
circulation become more important. Without full light the plant
develops
long stalk spacing between nodes (where leaves and
buds emerge). This will result in a weaker adult trunk,
more vulnerable to wind damage. A few species may require less
light, like tamarind. It's good to experiment with a groups of
seedlings to discover optimum levels of various parameters.
During germination air may be
circulated
with a fan but should be
refreshed from outside often. I had
great variance on the size of the roots and stalks on walnut
sprouts. Terminal buds on walnut, avocado and pomegranate
sprouts failed for no apparent reason. I suspect either asphalt
contamination in my sand, a pathogen in either the seed or soil, or
environmental contaminants.
Sprouts are extremely delicate and easily damaged. I've heard
that sprouts should be handled by their leaves. Sprout
roots
seem to be much less vulnerable to damage. At least with a guava
I
lost the taproot and it didn't seem to slow it down at all.
Nevertheless,
take
care on transplant because larger plants generally require their roots
to be mostly undisturbed. I've had a lot
of
dead terminal buds which result in a delayed sprouting of two or more
lateral buds. If you lose a terminal bud, snip the stalk
right above the topmost lateral bud with a sharp sterile
instrument. The topmost bud will develop at minimum
angle into the new
central leader and the wound will close up later.
Small seedlings with minimal root systems are more successfully
transplanted as bare-root than larger plants with extensive root
systems, because the larger plants are much more dependent on and much
less able to quickly regenerate their extensive sets of
micro-roots. So the larger the plant, the more important to
maintain the root ball on transplant. It is also much better for
these older plants to transplant during a slow or no growth period. In
any case, water the plant an hour before transplanting to
ensure it is not water stresses. Immediately water it well
afterward to settle the soil around the roots. Apply frequent
light waterings to compensate any root damage, until a day or two of
substantial growth, then taper off. Gradual tapering is key on
any change of environment (water, humidity, light and temperature) to
avoid shock. The general idea is to taper the daily dose over a
few days when changing rates.
Leaving sprouts in the germination tray for an extended period can be a
problem, despite their receiving plenty of light and water. Black
chilean guavas start out very tiny and I let them grow to about an inch
high before transplanting them. In individual pots they
started growing much larger stem and leaves above the spindly little
base. It's tempting to conclude that despite the extremely low
root density and abundant light and water, they were constrained by the
1" depth of the germinating tray or by root competition. I'm
suspecting that others such as pomegranate are reacting poorly to the
bounds of their pots, despite extremely low root density. The low
fertility of the germinating medium, sand, is another possibility.
Containers
Containers need to be well-drained. Waterlogged soil tends to anaerobic
fermentation which presents problems for most plants. In the
presence of oxygen, aerobic
decomposition proceeds and is much preferable for the plants.
Oxygen deficiency is lethal to the roots of most species. Fungi
can attack roots in these conditions in any case and is a leading cause
of plant failure in containers. Container culture risks moisture
extremes compared to the earth which
has a great averaging effect. The strategy is to simulate the
earth as much as possible. I cut
four vertical notches in the bottom edges of containers so water can
drain through either
the
bottom or the side. Any
old container will do but it should be strong enough so that when you
handle it the roots are not damaged. It should not secrete any
toxins. And it should be easy to deal with come transplant
time. Styrofoam cups are really handy for small plants because
they are so easy to cut apart on transplant. I cut the bottom off
first, set it in the new container then cut the side from top to
bottom, fill dirt all around, then carefully pull the styrofoam out.
The container may be sterilized by 10 to 20 minute exposure to direct
sunlight to avoid pathogen transfer. I also use 1/2 gallon wax-cardboard
milk cartons. I put a
strip of
packing tape around under the milk cartons so they'll last a few
months.
For long taproot plants I roll up newspaper around a four inch jar,
tape the seam with a strip of packing tape that goes under the bottom
and back up the other side. Then I make a newspaper bottom that
fits inside, and do another layer of sides and bottom inside without
tape. This makes a 12.5"x 3.5" container that may be planted in
the soil after the packing tape is removed. Nine of them fit in a
milk crate. Shallow germinating
containers don't need drainage because seeds actually enjoy
an occasional flood and the roots won't be sitting there a long time
to rot. Consistent regulation of moisture, air, light and
temperature are basic necessities to successful plant culture.
The container depth should allow the vertical growth of taproots, found
on the large, long-lived tree species and arid climate species.
Some species grow taproots much faster than the stalk but relative
growth rates are very species-dependent. Large embryos tend to
grow long taproots fast but so do some small ones, e.g. avocado can
grow
a three foot taproot before the stalk reaches eight inches, and carob
can grow a five inch taproot before emerging. When
the taproot reaches the bottom of a container it makes a 90 degree
bend and loops around in the container bottom. This usually
inhibits the taproots growth and function after planting out.
Depending on
taproot diameter and brittleness which is species-dependent,
looping taproots may be straightened on transplant but many species are
shocked when the growing medium is removed from the roots. If a
taproot
is damaged during germination or broken during transplant there's a
temporary vulnerability to pathogens until the break
heals. Generally, a broken taproot won't regenerate, so the long term
wind and drought resistance is penalized, but some
species are probably able to regenerate taproots. It has been
stated that a taproot
that stops at a container drain hole will
commence growing when planted out. An inverted cone shaped
container with an open sceened bottom might be good.
While waiting for the optimum time to plant out, re-potting may be
necessary to accommodate root growth. Although accommodating a
long
taproot is important for tall trees and arid-climate plants, in general
the container size is selected to balance root density. An
oversized container with sparse root density can be a problem for the
plant if the container is not well-drained and anaerobic fermentation
of organic matter in the soil develops, lowering the pH to excess
acidity. An undersized container with dense roots, i.e. "root
bound", will stunt plant growth and demand frequent watering to
avoid dry root stress. A root bound plant sends roots out the
drainage holes and above the soil surface. If you need to limit
their growth, many plants can survive in this state as long as you
prevent dry root stress but generally for optimum growth the container
size should be increased
at this point. Less water encourages more
roots while more water encourages more leaves. Keep a plant in
the same position after re-potting to avoid sudden change to its
microclimate.
Growing
Medium
Roots need oxygen as
well as water.
In soil, earthworms and other critters aerate the soil, but in
containers without critters a lighter soil type is needed for
aeration.
A popular potting mix is equal parts vermiculite, sand and peat
moss. Vermiculite is a volcanic rock that's been expanded by
heating with
air cavities like popcorn. It absorbs and releases
water and is structurally stable for a good while, I don't know, one
year to ten is a guess. Peat moss has similar properties as vermiculite
except of course it's organic and contributes to loam as it ages.
Loam is a mixture of sand/silt/clay
and organic matter. Silt is a very fine sand, and clay is even
finer. One problem with finer media like clay is that it can hold
too much water and easily suffocate roots. Another problem is
that when the water dries out,
layers of clay form barriers to air circulation. Some species are
more
vulnerable than others. Juvenile plants are
more vulnerable than adults.
If you're going to buy potting mix, buy sterilized, otherwise sterilize
your material by boiling for half an hour or baking at
200 degrees for an hour. Peat moss and alternatives, and
vermiculite and perlite, make for a lighter container. They also
allow the roots to more easily bind the soil mass together so the pot
can be pulled off for
root
inspection. The soil binding is also useful
in
transplanting. A small root system in a heavy mass of soil, sand,
silt or clay is vulnerable to root breakage in transplanting. I
had plenty of burlap on hand so I
shredded it into short length fibers and used that. It actually
breaks down much faster than peat moss. I
interleave
bunches of
it with spoonfuls of sand when filling a pot but
it's a slow process. I also add small
amounts of organic material like leaves. I top off the pot with
an organic mulch. This is needed because sand dries so quickly
and the mulch also supplies some nutrients. Again, all materials
should be sterilized.
Seedlings usually don't need fertilizing the first few months
because most soils contain enough nutrients. The breakdown of
peat and mulch provides a small amount but eventually some manure or
compost may be added in small amount at regular intervals. These
should be well-decomposed as this process usually causes plants
problems. Under the mulch but above the roots is probably
ideal.
I use purified water for small plants. Distilled
water may be better. Tap water may be ok but there are mineral
and chemical
contaminants.
If you use high-mineral tap water the minerals may accumulate over a
span of months and cause problems, so flush the soil with a lot of
water every 2 to 4 weeks. Softened tap water is full of sodium
which may be worst that the original minerals. Let the tap water
sit out 24 hours for
the chemicals to evaporate. This also lets the temperature
equalize with room/soil temp, preventing temperature shock. It's
also important to shake up a container of water to get
some oxygen dissolved in it. Sterilizing the water during the
sprouting period may reduce seedling defects. Water should be
kept off the plant except for an occasional mist to wash off
dust.
The amount of soil moisture is crucial. Too much and the roots
are
deprived of oxygen. Too little and the roots will dry out.
Both will kill roots and/or stress the plant, stunt it, and make it
more vulnerable to pathogens. But an occasional stress is good to
build strength. Try monitoring each plant's growth rate to gauge
the optimum soil moisture level and use a single soil mix for all
plants so it's easier to estimate moisture levels inside the soil
by the moisture level on top. Dig in with your finger to get an
idea of the usual moisture gradient with depth. Larger plants
with more leaves and roots draw water faster. Higher temperature,
lower humidity and higher wind draw water faster. You
should develop
a feel for the amount to water based on the plant and container
size, and adjust as these and the other factors change. An
occasional good deep watering will draw air
into the soil and flush stuff out. Alternate deep and shallow
waterings may benefit the plant by equalizing deep and shallow moisture
levels. Most plants have probably
evolved a dependency on occasional soil flushes. Given proper
drainage
holes in the container, you can put a tray underneath to catch the
excess water. But if the water in the tray is also standing in
the bottom of the container, any roots there will be vulnerable to
rot. You can empty the tray an hour after soaking, elevate the
container on a layer of rocks or paper, or put a layer of rocks in the
bottom of the container.
Indoor
Environment
Plants need maximum sunlight for maximum growth. If you're
growing indoors with artificial light you can extend the daily lighting
period
but the general limit is 18 hours for 6 hours of darkness.
My rule of thumb is to use a 5000K 23W compact fluorescent bulb per
one and a half square
feet of plant bed area for small plants and keep the plants about 5
inches from the
bulb. The distance seems to matter a lot. Farther and the
stalk nodes spread excessively, closer and the stalk nodes compress
excessively. I compared plants under this lighting arrangement
with plants on a balcony with only indirect sunlight. The balcony
plants have longer node spacing, and wider leaves. They also
seem to be softer despite the wind. They get some
blue sky on the balcony and they look as good or better than the inside
plants so I taped blue plastic
to the wall for the inside plants. Reflectors
can increase the
light available to the plants. I use heavy aluminum foil bent
around a football and fixed in the pot with wire to focus the light on
the plant. The reflectors should not be so large as to restrict
airflow. The plant pots should be turned/moved occasionally to
get even exposure unless you're planting them out flush against a
wall. The avocados developed a rust-like problem on the leaves
from being two to three inches from the light 16 hours/day.
Tamarind seedlings seemed to do much better in very low light but they
also had higher heat in that environment.
A key to growing plants is to duplicate their native
environments. Growing indoors
however provides the opportunity to accelerate their growth by
extending the daylight length, and the growing season to full
year. This can compress the juvenile period for seedling trees
that take several
years to bloom. I had a 5 month old mission fig cutting (from a
root sucker) with a 4 inch stem sprout
fruit.
Deciduous species will go dormant during their first winter, assuming
they can detect it. An approximate 33° latitude marine
environment (60°F night, 74°F day winter temps using some
generated heat), with close grow lights on 14 hrs/day, but with some
highly filtered window light was the environment I provided.
Pistachios leaves turned colors in the fall and dropped, not rebudding
until the next mid summer, walnut leaves got dead splotches in fall,
but kept leaves until next end summer, then rebudded. Maybe
providing them a colder winter temperature would have shortened their
dormancy and given faster bud break. Maybe providing them a
hotter winter temperature would have enabled them to skip
dormancy. It seems that these dormancies were not
stress-induced. I don't know if a lack of
chilling hours or the extended dormancy stressed these plants but they
did seem healthy after bud break, with the walnuts sprouting more
growth than their first season.
Regularly refreshed air from outside and good
airflow around plants is essential for indoor growing. So in
cooler seasons when airflow from outside is decreased, circulation with
a fan becomes
more important. Wind helps plants to
develop physical strength. Various pathogens are less effective
in a high
airflow environment. Plants have probably evolved a dependence on
wind to aid various processes.
Colder temperatures slows seedling growth but also lower the humidity
because colder air doesn't hold as much moisture. Some tropical
plant seedlings may struggle with lower humidity. In the colder
seasons indoor plants do better when the ventilation is kept to
something reasonable like one or two air changes per day, and the room
temperature is kept around 70 F. Humidity for the plants is
enhanced by keeping them close together, and keeping trays of small
pebbles or sand partly submerged in water under or near the plants, or
layers of wetted newspaper.
Knowledge of vegitative growth cycles and the lifecycles of leaves is
useful in determining
the health of plants. In a moderate indoor envronment, walnut
plants produced a flourish of large leaves over a period of two weeks
in late summer,
then then after another two weeks the leaves started to slowly degrade
over the course of a year, finally falling off at the next
budding. Papaya leaves have one to two month lifecycles with new
leaves constantly emerging in even spaced intervals.
Wolfberry and pomegrante leaves have two to three month
lifecycles, growing on new canes that emerge continuously. Almond
and guava leaves can last six months to a year on new stalk growth
throughout the summer. Avocado, citrus, carob and black sapote
leaves can last longer than a year, with growth emerging in the
summer. Avocado and citrus have a long growing season, carob and
black sapote is short. Pistachio leaves bud out once in a quick
flourish
that lasts about six months, slowly turning shades of red over the last
three, then drop and leave the stalk bare for another six.
Pistacho, carob and black sapote are relatively slow growing.
Fig, cherimoya, capulin cherry and tamarind are nearly continuous
growers with leaves lasting six months to a year. Climate and
cultural variables can alter growth cycles of course. To some
extent, plants scavenge nutrients from old leaves before
dropping them.
Pests
and Pathogens
Fungus gnats can feed on roots and cause problems. Heavier
waterings at longer intervals controls them by moving the moisture
depth lower, with a risk of stress to the plant. Maybe experiment
with small containers of water. The gnats land on the water and seem to
get
stuck there.
I had severe spider mite infestation on my almond seedlings. It
first showed up as a yellow patina on young leaves and bronze patina on
older leaves. Finally, I noticed the tiny spider webs around the
terminal buds and the tiny white mites crawling along them.
Later I found an infestation causing dark rust on pistachio
leaves. They can easily kill the the seedlings by destroying all
of their leaves. They tend to congregate and do the most damage
on the sides of the leaf's main stem, on the stalk end, on the
underside of the leaf. The mites had to be rinsed or brushed off
into a wash basin and flushed away, something like twice a week,
ongoing. Later, I found them infesting almost every species,
really causing problems on citrus. Broad mites attack the
terminal buds resulting in severely distorted leaves. They may
cause aborted leaves, as I had plenty of aborted almond and citrus
leaves, but I can't rule out light and temperature.
I had a problem with prunus seedlings developing bud gall where the
terminal bud grows in a knot. It seems to be solved only by
snipping the stalk well below the knotty node. Use a sterilized
sharp razor to minimize damage. Some
wolfberries were spindly, had very yellowish leaves and dying leaves at
the bottom. I don't know if they developed some kind of disease
or if their soil was somehow contaminated. I got the sand from
the city which may have mixed in a little asphalt.
My walnut seedlings developed what I believe to be leaf blotch from
anthracnose fungus. It seems to have developed after I closed the
outside ventilation although I kept a fan circulating the inside
air part-time. The fungus is said to spread by wind-borne spores
ejected from dead
leaf material during cool rainy periods. Removal of dead leaves
helps limit infection of new leaves. The original spores were
probably on the nut shells. It's probably a good idea to clean
them before sprouting or remove the embryo and wash them
carefully. One application of dissolved baking soda failed to
stop the fungus
spread. My guess is that that ventilation time and intensity
matters. I left the fan running non-stop with a faint flutter of the
leaves and it seemed to halt the spread of the fungus. The fungus
stopped growing and the leaves remained about halfway covered throught
heir life cycle.
Another black rust of some sort has attacked the chilean guavas,
carissas, pistachio, cherimoya, citrus and guavas. On chilean
guava and carissa it forms a scale on the stem, attacks the leave
underside on each side of the leaf stem but not the leaf stem.
This scale seems to be carried by the mites. On
pistachio it attacks the main stem, terminal bud, underside of leaf,
and leaf stem. On cherimoya it attacks the main stem, terminal
bud, underside of leaf stem. On citrus and guava seedlings it
attacks the terminal buds, and on larger guava it develops a scale on
the stem and may be the culprit in killing new leaf growth. It
always stunts leaves and kills the terminal buds, though cherimoya
terminal buds seems to survive but are severely set back. I tried
a mixture of one part each baking soda, olive oil and mild dish soap to
100 parts water, coating the leaves stems and buds. It seems to
have helped, but may need several applications. This mixture also
works on the mites.
Another sort of rust appeared on the avocado leaf tops wherever there
was direct exposure to light. One of the avocados has had aborted
bud
growth, which may or may not be the result of this pathogen. I
had an outbreak of mealybugs on figs and wolfberries. I had an
outbreak of scale on one fig and it is trying to expand to
others. I'm testing the baking soda/oil/soap mixture on
that. A white cottony fungus attacked the pomegranates after an
outbreak on wet newspaper pots.
So it seems pests and pathogens are a big challenge in a seedling
nursery. Various strategies include consistent air circulation,
long dry periods between watering, regular inspections with magnifying
glass, manually picking off, brushing, cleaning with water streams,
weekly soda/oil/soap applications, qurantine or systematic isolation of
seedlings, selecting individuals with higher tolerance, and keeping the
plants as strong/healthy as possible.
Planting Out
Planting out has to occur before the seedling is stressed by root
containment. This of course varies with species but nurseries
generally keep seedlings in containers for one to three years.
Long taproot species natually outgrow containers first.
The plants have to be slowly acclimated to the outdoor environment over
a period of one to several weeks with a couple days in the hole to
equalize
soil temperatures, checked with thermometers. On any transplant
the soil height on the trunk should be preserved as many species may be
killed by
burial of the trunk. Keep mulches off the trunk. Keep the
trunk exposed down to the root flair. The ground and container
soils should be blended at their interface. The reason is that
water likes to disperse but likes to pool more, so a smoothly changing
interface
promotes dispersion over pooling. Get some extra soil of the type
in the container to mix with the ground
soil in the interface area. Generally plants like a significant
radius
of this mix to build new roots in. Cut the bottom of the
container off, snip any curled roots on the bottom, place the container
in the hole, slit the side of the container while keeping it on,
lightly fill in around container with soil mix, then carefully pull the
container out. Tamp lightly and water heavily to settle the
soil. Water well until roots are established. Protect
from sun, heat, cold, wind and pests.
Pruning is performed
to develop a strong tree structure to support larger crops later
on. Pruning
encourages vegetative growth and suppresses reproductive
growth. A non-pruned tree will flower and produce fruit sooner
than a pruned tree. Node/branch heights
remain
fixed as the tree grows. A tree will generally shed lower
branches as
it grows higher branches unless you keep it as a shrub by
pruning the central leader. Prune lateral branches right above
the
branch collar for
better wound closure than a flush-to-trunk prune. A 90 degree
angle is the strongest branch
angle because there is maximum
connective wood on the top side of the branch supporting it against
gravity and wind.
Weak branches often break under fruit load.
Outdoor
Microclimates
You can choose only
species well-adapted to your general climate, find the microclimates
in
the yard most suitable for a species' individual needs, and add a
microclimate enhancement for very alien species.
This is
obviously the
most work, but may be limited to a seasonal chore, only during the
plant's juvenile period.
An example would be to get tropical plants to grow and produce fruit in
an arid climate. The potential problems in this example are too
much heat in the summer, too much cold in the winter, and too little
humidity. Wind lowers
humidity so the strategy to maintain humidity would include wind
breaks,
made of native species of trees and shrubs on the perimeter, plus the
more arid-tolerant
members of the orchard closer in. Training the plants as
low-growing
shrubs instead of trees also reduces exposure to wind and provides
increased ground heat radiation to the plant (frost protection).
Other benefits of
low-growing forms include ease of
maintenance and harvest, and reduced trunk exposure to sunburn.
Mulching reduces water loss to soil evaporation and helps moderate soil
temperature in extreme heat. Wind breaks reduce water loss
to transpiration and moderate air temperature, which can be important
for some plants in extreme arid climates. Wind breaks on the
north side often protect against cold wind and on the south side
against hot wind, but this is only a generality. Natural
convection usually causes colder air to move down slopes and can pool
in a valley or where obstacles, including plant growth and
buildings, break the drainage to lower ground. It may be
necessary to break up hedges
along the lower side of the orchard to improve air drainage in the
winter. But if heat in the summer is a bigger issue,
the wind break on the lower side may be beneficial.
A plant's summer sun exposure may be limited by
positioning another plant on its east or west side. For plants
vulnerable to both light and heat stress, the west side shade provides
protection during the hotter part of the day. A building may
also provide shade. Tropical plants grown in higher
latitudes generally want maximum sun in the winter so the
equator-facing exposure should be maximized. If a light-colored
building or wall is present on the opposite side this can
increase the light on the plant through reflection. For plants
vulnerable to
frost damage, a nearby wall may also provide some thermal averaging,
especially massive materials like stone. Soil around and upwind
of plants also provides thermal averaging if the sun is allowed to
reach it and the top foot is kept relatively firm and moist.
Darker, denser soil absorbs more heat. Thermal averaging may
even protect temperate climate plants and their flowers that are
vulnerable to
rapid temperature changes.
More intensive climate management involves rigging straw or plastic
screens around plants. Full enclosure in black plastic
screen may
reduce sun and
wind, increase humidity and also serve to keep birds from stealing
fruit while allowing pollen and insects through. Clear plastic
sheet may allow nearly full sun to penetrate
while lowering wind and raising humidity, but plenty of ventilation is
needed to avoid overheating. White plastic sheet provides
wind/humidity control and reduced light/heat. All such
coverings reduce
the chance of frost damage by reducing heat loss to both wind and
sky.
For young tropical
plants in higher latitude arid climates, a plastic or straw sunscreen
on top and east/west sides, and a high-mass wall on the
side
opposing the equator reduces light/heat in the summer, breaks wind from
most directions, and increases light/heat in the winter. Add
chicken
wire on the open side for critter control. Closely
spaced stakes in the ground may also be necessary to thwart burrowers
and root chompers. Any rigging
has to withstand wind and rain so it doesn't collapse on the
plant.
Effectiveness of high-mass walls in moderating heat
depends on the amount of mass in the wall. In humid climates, the
wall can attenuate the seasonal
heating/cooling cycle peaks in proportion to the amount of
mass, but in arid climates the greatest benefit may be with
an amount of mass that phase-shift-cancels the diurnal heating/cooling
cycle (fun experiment with thermometers). The wall
surface
treatment affects the level of heat
radiation and light
reflection during the winter. For higher frost risk, paint
the wall surface a darker color so it will collect more heat, and
for lower frost risk lighten the
color, which benefits the plant with more reflected light.
Other means of dealing with frost include wrapping trunks with
insulation (may
require fungicide treatment), and draping blankets, tarps or
plastic over the tree (or better still, a frame around the tree).
Soil warmth provides a good deal of frost protection to plants.
With generally sunny, warm and calm conditions, exposing the soil to
the sun may increase soil warmth to help guard against unpredicted,
sudden frosts, but in low light, low temperature or high wind
conditions, mulching may be used to preserve soil warmth. Either
way,
increased soil moisture (for tolerant plants) increases the frost
protection benefit.
The intensive climate management strategies that moderate the seasonal
climate changes are best applied incrementally over a period of days or
weeks but should not start too early in the season because plants need
to experience seasonal changes to fully acclimate to them, to maximize
their tolerance to weather extremes. Timing and rates of
fertilizer, water and pruning also affect acclimation in various ways.
Climates:
Tropical - 75°F - 95°F with seasonal and diurnal consistency
Malcolm Beck's articles on organic agriculture
Copyright (c)
2005, 2006, 2007
Robert Drury
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Disclaimer: This information may contain inaccuracies and is
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