Over-watering gardens wastes time and resources but may not do serious harm to plants in well drained soil. Poor drainage causes diseased plants, reduced or lost yields and very often the quick death of vegetable plantings. Few vegetables or fruits thrive in constantly wet ground. Spot signs of poor drainage before locating the garden--correct the problems or move along.
Poorly drained ground often carries a nearly constant layer of surface water in the wet seasons of winter. Ground that stays muddy for days after nearby areas firm up indicates drainage problems. In plowed or tilled gardens with this trouble, water stands on the surface between rows rather than soaking into the ground.
In grassy areas with poor drainage the grass itself often yellows and dies, leaving bare soil. In fertilized soil including gardens and fields, standing water dissolves soil salts which stay behind when the water evaporates or seeps away. A white powdery layer on bare low spots in the garden during dry spells indicates stagnant conditions.
Crops which yellow and die a few days after a good rain could be afflicted with phytopthora root rot. This disease softens and kills the roots of plants and attacks stems where the plant emerges from the soil. Damp conditions also contribute to the growth of damaging molds and other leaf diseases. Poor drainage provides perfect conditions for fungal disease.
In heavy clay soil even the lay of the land can be a sign of drainage trouble. Shallow basins surrounded by long gradual slopes could be inundated by runoff frequently during the year. Sandy loam could quickly drain the extra water away, but without an outlet a clay basin becomes a temporary pond. When tilling gardens in the spring, a low spot never quite dry enough to work without problems shows a hidden drainage problem.
Digging a six inch diameter test hole three feet deep reveals the degree of the problem. Fill the hole with water. In a well drained location the hole should empty within a day. Fruit trees as well as vegetable crops could prosper there. If drainage takes two days or more the site could be troublesome. The deep roots of trees could be seriously damaged during wet weather. If the hole fills with water on its own, plant the garden elsewhere. The top of the soil should be at least two feet above the water table even for most shallowly rooted crops. Installing drainage tile at that depth could make the location usable for vegetables and berries.