WEED CONTROL

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 Fertilizers.

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.

Beneficial weeds
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 plants.

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.

Control methods
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.

Cultivation:
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
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.

Close Spacing:
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.

Other Practices:
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.

Herbicides:
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.