began my first containerized vegetable garden about eighteen months ago.
Shortly after harvesting that crop, I began getting e-mail requests for
information about growing food on patios and balconies. Amazing! The Principle
of Serendipity guides me to assist the Universe’s intentions. It seems I have
been appointed to help those who don’t own land grow some of their own food.
Okay, Universe, I accept this mission. Besides, container gardening is so
interesting that I am delighted to expand my research.
Containers are small
dwellers who live on small lots often grow food in enclosed raised beds filled
with soil or a purchased growing medium. Apartment dwellers with balconies,
patios, or bright sunny windows try to grow food in pots. All are forms of
main challenge of container gardening is that plant roots are restricted.
Plants grown in the field enjoy a depth and breadth of root development that
can’t be duplicated in containers. Plants feed and absorb water through newly
formed cells extending back from the root’s tip for less than half an inch. The
tip remains active for—at most—a few days. As the root tip extends deeper into
the soil, older root tissue develops a hard skin and becomes a conductive tube
that carries the moisture picked up by the ever-expanding tip. To
remain well fed, a
plant must constantly develop new roots.
When growing outdoors in natural soil, the gardener limits root-zone
competition by giving each plant sufficient space, so it won’t have to struggle
with other plants for water and nutrients.
best guess is that to raise a single lettuce plant to maturity—that is, one
full-sized high-quality head—before becoming pot bound you’ll need three
gallons of rich, loose soil in an ordinary plastic pot. Five gallons of growing
medium will support the full development of one compact bush tomato for almost
three months before it becomes pot-bound. The moral: use a BIG container and be
alert for signs of stress that appear on pot-bound plants.
Fertilizer for containers
It is possible to support
containerized plants so they remain healthy and continue to grow after their
root development becomes restricted. There are two approaches: use a growing
medium that encourages development of a denser root structure (to be discussed
in next month’s article); and fertilize your irrigation water. Home gardeners
routinely fertigate (my word, combining fertilizer with irrigation) using rapidly
soluble chemicals with a 20-20-20 analysis, or use prepared liquid organics
such as fish emulsion or liquid kelp. Gardeners also fertigate with tea made by
soaking compost in a bucket and then diluting the dark liquid that is poured
off; worm compost drippings also act like liquid fertilizer. Sadly, and for
various reasons, none of these approaches work nearly as well as is possible.
all soluble chemical fertilizers fail to provide complete, balanced nutrition.
They lack one profoundly essential element—calcium—needed in considerable
quantity by almost all food-producing plants. These fertilizers also lack other
minor nutrients. Soluble fertilizers may be too high in nitrogen to suit many
fruiting plants. Plants grown on soluble chemical preparations alone almost
inevitably become diseased or are attacked by insects. If you must use such
fertilizers, mix them at one-third the strength recommended by the maker and
always use this dilute fertilizer to irrigate plants. If
it is a fruiting
plant, use this fertilizer only while the young plant is not yet bearing fruit.
tea, compost tea, or worm tea will not, by itself, create maximally healthy
plant growth. These fertilizers provide complex organic nutrients similar to
those that plants obtain from the biological process of living soil (but not
nearly as complete). Feed containerized plants at least once a week with
compost or worm tea, or with liquid seaweed. Dilute these organics to roughly
half the strength recommended, because you will provide the majority of the
plant’s nutrients from natural organic fertilizers mixed into the growing
medium itself. These mixtures can fully nourish a plant for the first 10 to 12
weeks or until it becomes pot bound.
need different kinds of nutrition when making fruit (not just
tomatoes—botanically speaking, snap beans are fruit, too). During fruiting, the
plant’s rate of vegetative growth slows—it will not form as many new leaves.
The leaf contains most of the plant’s chlorophyll, a protein whose manufacture
requires most of the nitrates the plant can accumulate. Consequently, a
blooming and fruiting plant needs less nitrogen than one growing a new, leafy
structure. Because fruiting involves seed formation, flowering and fruiting
plants use more phosphorus and potassium than they needed when growing only
Soluble chemical mixtures
designed for blooming and fruiting plants are often formulated as 5-10-10 or
10-20-20. They do a better job than a 20-20-20, but these chemical combinations
share the same failing as the higher nitrogen formulations. They are usually
formulated with the least costly—and thus less effective—forms of chemicals.
out on the right foot when potting up your plants. Make the soil itself fertile
enough to grow your plants without adding anything but water while the plant is
building leafy structure. That means blending your potting soil with organic
fertilizer. To each gallon of soil, blend in one-half cup of my complete
organic fertilizer (COF) recipe or something similar, such as Down-To-Earth’s
Bio-Live or Bio-Fish organic fertilizer.
COF will release its
nutrients within 90 days of mixing it into soil. Organic nutrients may not
release as quickly if you use a non-soil growing medium such as commercial
bagged potting soil. In that case, you may need to use liquid fertilizers, too.
Add one heaping tablespoon of finely ground agricultural lime to each gallon of
soil unless you are using COF, which already contains lime.
Your plants may grow longer
than 90 days, so will require additional fertilizer. If you are growing leafy
crops whose harvest goes on longer than a month (kale, broccoli, or a
cut-and-come-again pot of salad greens) their growth rate will taper off as the
COF is absorbed. When this happens,
almost any high nitrogen liquid fertilizer will work well, but
only if the plant has
enjoyed a few months growing on COF first and if the soil mix contains lime.
about fruiting crops? This may surprise you, but the best fertilizers for
container plants are not sold in garden centers, but in places that supply
indoor growers of cannabis. And the best of these fertilizers are not the
organic products, but the chemical ones. The production of cannabis under
artificial lights is probably the largest containerized growing industry,
planet-wide. Indoor pot growers have a profound interest in maximizing yield
a halide shop (so-called because halide lights are used by indoor growers)
you’ll find nutrient solutions developed for both soil and hydroponics. Some of
the more costly liquid fertilizer concentrates found in such shops contain
calcium. These expensive liquid chemicals may also contain chelated minerals.
Plants are able to absorb chelates far more effectively than when they are
offered simple chemical salts.
have had extraordinary results using a concentrate made by the Canna Company
called Terra (soil) Flores (flower). The results of using Terra Flores are
astonishing when compared to dry chemical “bloom” fertilizer to support
fruiting peppers. I suggest mixing the fertilizer into all irrigation water
from the time the plants start forming fruit. However, Terra fertilizers aren’t
cheap! Using the Terra Vega (for leafy growth) to produce lettuce might end up
costing you several dollars worth of fertilizer to produce a single head—it’s
best to use COF in the soil. But to use something like Terra Flores to support
the development of tomatoes once the fruits start forming, it might cost a few
dollars per tomato plant, but will increase the yield (and maybe quality, too)
final warning about using fertilizer concentrates on container plants: if you
use COF fertilized soil, dilute all liquid fertilizers to about half the
recommend strength and only very cautiously increase the strength beyond that.
If you start to see brown tips on your leaves, immediately reduce the
concentration to half-strength or use pure water for a week and then reduce the
concentration to about half of what is recommended.
Notes: See northwestgardennews.com
for Steve’s COF recipe; Down to Earth fertilizers are at
www.downtoearthdistributors.com/fert_blends.html; in Seattle, visit Walt’s
Organic Fertilizer. Canna fertilizer products are available in the U.S. online
at greenhouse supply sites, including hydroasis.com