Wet conditions in gardens can result from a low garden location or from water flowing onto the garden from higher elevations. Leveling the garden to eliminate low places, sloping the surface toward a drain, or raising the garden's center to permit drainage away from the garden may be helpful. In some places each row is planted on a slight ridge rather than in the furrow because drainage is improved and the top of the row warms up sooner in spring.

Organic matter The importance of soil organic matter cannot be over-emphasized. Almost any soil can be made fit for growing plants if enough organic matter in the form of decayed leaves, compost, peat moss, decayed sawdust, ground bark, or animal manure is added.

Dark brown to black colors indicate a high organic matter content. Natural topsoil contains the largest amount. That is why it's important to locate the garden on undisturbed soil if at all possible This also is the reason that top soil should be stockpiled during grading for construction and then used as the final top dressing.

Organic matter has several functions. The most important is as a source of plant nutrients and as a soil conditioner. Organic matter adds body to sandy soils. It increases the capacity to hold moisture and nutrients. It promotes granular structure in clay soils, which aids in root growth and the entrance of water and air into the soil. It makes the soil easier to till, results in better seedbeds, and reduces crusting that affects emergence of seedlings.

Raw organic material is decomposed by soil micro-organisms to produce humus and release nutrients that are used by plants.

Animal manure has a fairly good balance of nutrients and decomposes rather rapidly. On the other hand, sawdust has a low level of nutrients (especially Nitrogen) and decomposes rather slowly. However, decomposition can be speeded up quite markedly by adding generous amounts of fertilizer (particularly Nitrogen) to sawdust compost or to soil into which sawdust has been incorporated. The same applies, to a slightly lesser extent, to other "woody" organic materials such as ground bark, leaves, and grain straw.

Organic materials added should be worked into the soil's upper 3 to 6 inches. Such matter needs to be added each year on most soils. Don't use organic wastes contaminated with weed seed or pesticide residue.

Soil moisture and watering If a soil has been saturated by rainfall or irrigation and then is drained by gravity until the larger pores are free of water, the soil moisture content is at field capacity. This takes a few hours. When plants have used up the available moisture and permanently wilt, the soil moisture content is at the wilting point.

The amount of water in the soil between field capacity and the wilting point is the available water capacity. Compaction decreases the water-holding capacity and additions of organic matter increase it slightly.

Plants vary in their water needs. Water requirements also vary with the soil conditions and the climatic conditions.

Most garden plants require about 1 inch of water per week. A soil with the capacity to hold .1 inch of water per inch of soil can supply only a week's growth with roots in the top 10 inches of soil. If rainfall is less than 1 inch per week, supplemental watering is required.

Know your soil. For example, the water-holding capacity of the soils of the District of Columbia ranges from .04 to .26 inches of water per inch of soil. The soil with the lowest rate will need watering every 3 days during the growing season, while the soil with the highest rate can support plant growth for 2 1/2 weeks without watering.

Contoured garden saves water and reduces soil erosion.

Plan a watering schedule that fits your soil and climate. Start watering when about a third to half of the available water has been removed. Do not apply more water than the top 10 inches of soil can hold. Most garden sprinklers apply about a quarter of an inch of water per hour.

Slope and erosion control Some slope is desirable on most gardens to eliminate wet spots. About 1 foot per 100 is usually enough. On strong slopes water may run off too rapidly, eroding the topsoil and carrying away organic matter and plant nutrients. Contouring or terracing permits the water to move across the slope instead of down. Thus the soil absorbs more rain and is less susceptible to drought.

To contour a garden, make rows across or perpendicular to the slope of the land. This does not require special skill or equipment. An efficient device can be made from an ordinary carpenter's level mounted on a long 2 by 4. Lay the 2 by 4 across the slope and move one end up or down until the bubble on the level is centered; mark the spot with a stake. Repeat the process across the slope to establish the contour guide line.

Plant the rows of vegetables parallel to this line. As you cultivate the garden, leave small channels between the rows to collect and hold the moisture so that it soaks into the soil.

Surface drainage may be required on some soils. You may need to give a slight slope to the contoured rows to provide for drainage.

To lay out contour line, use carpenter's level mounted on 2 by 4.