VEGETABLE GARDEN: WEED
CONTROL IN THE GARDEN
Ch.10, pp. 25 - 29
The amount of fertilizer to apply to a garden depends
on the natural fertility of the soil, the amount of organic matter
present, the type of fertilizer used, and the crop being grown.
The best way to determine fertilizer needs is to have the soil
tested. Information on soil testing and a list of testing
laboratories is available through your local Extension agent. Soil
test kits are of little value to gardeners in Arizona. Vegetables
fall into three main categories according to their fertilizer
requirements: heavy feeders, medium feeders, and light feeders. It
may be advantageous to group crops in the garden according to
their fertilizer requirements to make application easier. Refer to
table 10.1 for a listing of crops and their nutrient needs. For a
complete discussion of fertilizers, refer to Chapter 2, Soils and
WEED CONTROL IN THE GARDEN
The old saying, "One year's weed - seven years' seed,"
contains more truth than myth, as most gardeners soon learn. Weeds
(some native and some introduced) are remarkably adapted to
conditions in the area where they grow, usually much more so than
the imported cultured vegetables we prize so highly for food. Many
weeds which would otherwise not be growing in a lawn or natural
area appear to spring up as if by magic when the soil is
cultivated. Weed seeds may remain viable for those 7 (or more)
years when conditions are not right for their growth. Then,
brought to the surface by tilling, and uninhibited by sod, shade,
or other factors, they germinate and become the pests that take
water, nutrients, sunlight, and space from vegetable plants.
Many plants considered weeds in the garden have positive
attributes. Some, such as the Venice mallow (or
flower-of-an-hour), morning glory, and even thistles, have flowers
that rival those intentionally planted in flower beds. In fact,
seeds of some weeds are sold by seed companies as flowering
Other native plants are edible, providing nutritious
variety to the regular diet: dandelions, purslane, chickweed,
cress, mustards, and lamb's quarters all offer greens;
blackberries produce sweet fruits; Jerusalem artichokes, or
sunchokes, are nothing but the tubers of the native sunflower; and
of course, there is always wild asparagus. Before attempting to
eat wild plants, be sure that you have properly identified them. A
course from a person knowledgeable about wild edibles is probably
the best way to learn; books often do not make fine distinctions
between edible and non-edible wild plants.
Weeds are often a habitat for various insects, some of
which are beneficial to the garden. They provide shelter, pollen,
and nectar for such insects as bees and predators of garden pests,
such as praying mantids.
Wild plants also have other virtues. Parts of some
plants are used in natural dyes and other home-made products.
Weeds can be a good source of nitrogenous materials for the
compost pile if pulled before flowering. Many have long roots
which bring elements from the subsoil into their above-ground
tissues; when the weeds are pulled or tilled and allowed to decay
in the garden, these elements are made available to other plants.
Finally, the presence of some native plants can indicate certain
soil problems, e.g., deficiencies, pH changes, soil compaction,
etc. A small number of books are available with detailed
information on this subject.
Despite all this goodness, most gardeners won't tolerate weeds in
their vegetable plots. Perhaps it is an overreaction to the first
garden he or she allowed to go completely to weeds or perhaps it's
the unruly appearance of weeds. This may be a sensible approach.
If one doesn't have time to ruthlessly destroy morning glory vines
after enjoying the first few flowers and before they go to seed,
the garden will soon become one glorious display of morning
glories and little else.
There are several ways to rid the garden of most problem plants.
Since mature weeds extract large quantities of moisture and
nutrients from the soil, it is more beneficial (and easier) to
remove weeds when they are young and tender. Hand-pulling and
digging are okay for small gardens and raised beds. Those with
larger spaces usually prefer at least a hoe. There are
manual-powered rotary cultivators that do a good job on long rows
and pathways as long as the soil is not too wet or dry and the
weeds are small. In large gardens, a rotary tiller of appropriate
size makes the work easy and fast, but it is not the most pleasant
chore to get behind a smoky, noisy engine on a hot summer day.
Manual and powered rotary cultivators are usually unable to turn
under weeds very close to vegetable plants without damaging the
vegetables. Hand-pulling or hoeing with a light touch are best for
removing weeds near vegetable plants. Deep cultivation with any
instrument is likely to damage roots or stems of crop plants.
Turning under weeds, especially before they flower,
provides organic matter to the soil. Hand-pulled weeds, except for
rhizomatous grasses, may be laid on top of the soil to dry out and
will eventually have the same effect. However, if rain is
predicted in the area within a day or two, it's best to collect
the weeds and add them to the compost pile; rain will wash soil
around the roots and some weeds will survive. If weeds have
started to go to seed, leaving them in the garden is not a good
idea. Composting may not destroy weed seeds if the pile doesn't
heat up enough after the weeds are added. Grasses that spread by
rhizomes or stolons also present a problem if not completely dried
up. In these cases, despite their potential value as organic
material, it's better to let the trash collectors take the weeds,
or burn them and spread the ashes in the garden (if local
ordinances permit). Reducing weed growth around the garden by
mowing or other means will also help prevent the spread of weeds
and seeds to the garden area.
Cultivation is best done when the soil is somewhat
moist, but not wet. Working wet soil will change the structure,
especially of heavy soils. When it is too dry, weeds are difficult
to pull and hoeing is also hard. A day or two after a rain or
irrigation is probably the best time to cultivate. If you have a
choice, remember that the work will be much more pleasant in the
cool temperatures of early morning or evening. On hot summer
afternoons, you are likely to fatigue more easily, get a sunburn,
or suffer from sun poisoning, heat exhaustion, or sunstroke. Wear
protective clothing if you must work when it's sunny, and stop
frequently for rest and refreshment.
Mulching can be an alternative to weeding if you have a reliable
source of mulching materials. Thick layers of organic mulch will
not allow most annual weeds to poke through, and those that do are
usually easily pulled. Weeds with runners are often not so easily
controlled, and black plastic may be a better choice where these
prevail. For paths, newspaper, old carpeting, or other such
materials, covered with sawdust, will provide excellent weed
suppression. However, sawdust is not recommended for use right
around plants because of its tendency to crust. The bacteria that
breaks down sawdust takes nitrogen from the soil, and thus from
vegetables. Mulch can also be used to modify soil temperatures.
Inorganic mulches (plastic sheeting, weed mats, etc.) warm up the
soil, while organic mulches (sawdust, compost, straw, newspaper,
grass clippings, etc.) cool the soil. Plant growth can be enhanced
by matching the right mulch to the type of crop and weather.
Inorganic mulch can be used early in the season to heat up the
soil then an organic mulch can be applied later on to cool the
soil as summer temperatures raise.
Once vegetable plants are established, if they have been planted
close enough to each other, they will shade the soil and prevent
the growth of many weed seedlings. This is the effect achieved by
a well-planned raised bed, in which plants are spaced so that the
foliage of adjacent plants touches and forms a closed canopy at a
mature growth stage.
Some gardeners are experimenting with various types of no-till
gardening to reduce weed problems and prevent erosion and moisture
loss. The standard farm no-till practice of sowing a fall cover
crop and then killing it with a herbicide, and planting vegetables
in the dead sod, after a recommended waiting period, is one
method. However, there are no herbicides recommended for use in
established home vegetable gardens to kill emerged weeds at the
present time. Use of weed-killers normally recommended for lawns
or other areas is not advised, and until a safe herbicide is
available for growing weeds, this type of no-till practice is
unsafe for growing vegetables in the home garden. One alternative
is the use of a living sod, mowed regularly, which has many of the
benefits of no-till and does not necessitate the use of
herbicides. This practice works best with raised beds, so that
only the paths need to be mowed.
The use of cover crops over several seasons or years in
a particularly weedy section can also reduce weed problems.
However, this method requires leaving that part uncultivated,
reducing gardening space. Cover crops must also be mown or
harvested regularly, which can be time-consuming and/or difficult
without appropriate tools. Investigate crop rotations thoroughly
before using them to control weeds. All of the above techniques
are still in the experimental stage for home gardeners. Try them
in small sections of the garden to determine their effectiveness.
As mentioned before, herbicides may be used in and around the
home garden, but special care must be used to insure it is applied
safely. They should always be used according to label instructions
and only for crops listed on the label. The wrong herbicide can
destroy a garden's productivity for years. Even when used
properly, drift from herbicide sprays used on lawns or in areas
surrounding the garden can cause damage to vegetable plants, so
take care to spray on windless days and erect barriers to protect
plants if necessary. Drift from pre-emergence herbicides does not
damage growing plants, but may prevent seeds from germinating. Be
aware that treatment with an herbicide for one type of weed may
result in the area being colonized by other weeds which are
tolerant to the chemical. Finally, never use a herbicide in the
same sprayer used for insect and disease control. Keep a separate
sprayer for plant-killers only.