If our ideal Gardener's Loam has been built up, the only barrier to correct control of air and water is drainage. This is a basic requirement, but it is often left to chance. I have seen carefully-worked gardens where a loose, friable soil had been created, but no provision made to lead away water which found this loose soil easy to penetrate. As a result, the area (surrounded by an underlayer of
hard clay) became a "bathtub" into which moisture drained, forming a swamp during wet weather.
To check drainage, try to obtain a water-tight barrel or a steel drum that holds about 50 gallons of water. Fill this and then upset it over your garden plot or lawn. If the water soaks in within a few minutes without forming puddles, consider yourself lucky. If it runs off quickly and little of it is absorbed by the soil, grading to reduce the slope may be necessary.
Grading sounds like a real engineering job, which it often is if done on a large area. However, the slope of a small garden, perhaps 30 feet across, should be easy to change so that runoff is slowed up and water penetrates readily.
The trick is to use "cut-equals-fill" techniques. If you want to change the grade ten inches, don't take all ten inches off the top side. Instead, remove five inches from the upper end of your garden and add it on the lower end. This sounds complicated, yet can be carried out over a weekend or two without too much work.
CORRECTING POOR DRAINAGE
If water from the upset barrel remains on the surface for several hours without soaking in, or if water stands there for several days after a spring rain, drainage is poor and must be improved. A basic principle is that water must have some place to go. No matter how well prepared soil may be, it can become waterlogged if no outlet is provided for excess moisture during spring or other periods when rainfall is heavy.
Check both absorption (by the upset barrel test just mentioned) and accumulation. The latter can be tested by digging a hole about 18 inches deep in spring and watching to see if water accumulates and stands in it following heavy rains. If so, then a drainage line of tile should be run to a lower point to take off excess moisture. If the garden soil is loose and friable, this line need not cross the garden at all, but can run from the lowest corner of the plot to some lower area of the property. On small city lots a drain into a storm sewer may be necessary, since few such lots are large enough to allow digging a line to a lower spot.