It is difficult to grow vegetables and flowers in sandy soils but it can be done successfully if a good level of soil organic matter is maintained. This was shown by some recent research in Connecticut.
A three-inch layer of leaf-mold (partially decayed leaves) mixed with the top six inches of soil made the difference. With so many tree leaves available for composting in the fall, many gardeners can prepare a lot of leafmold.
Buildings in downtown New Haven had been demolished and the New Haven Arts Council proposed to use the site for a community garden. Dr. David E. Hill, Connecticut Agricultural Experiment Station soil scientist, was asked what plants would grow in the existing soil and what could be added to the soil to make crops better.
"You've got to be kidding," Hill explained when he saw the sandy soil and rocky debris that had been left behind.
"Because of the poor soil on the site, I saw an opportunity for experiments with soil treatments to learn how urban gardens could be best established on vacant land," he said. "I worked with 61 families who were able to grow some of their own food a short distance from the New Haven shopping district. Knowing that the largest problem, other than the lack of nutrients, was the low wate-holding capacity of the soil, I designed several experiments to find the best conditions for plant growth.
"In the first plot, I had a three-inch layer of leaf-mold tilled into the soil to a depth of six inches; in the second plot, six inches of a finer textured topsoil was spread over the sandy soil; in the third plot, sheets of newspaper mulch were buried to reduce evaporation; and in the fourth plot, I grew vegetables under the same conditions as other urban gardeners.
"All my plots received optimum fertilization, based on soil tests, and were watered from a nearby hydrant as needed. The vegetables grown included string beans, onions, summer and fall squash, tomatoes, cabbage, broccoli, eggplant, peppers, lettuce, beets and carrots."
The native soil in the untreated and paper-mulched plots retained less than one inch of water in the upper six inches of soil at field capacity, with only one inch available for crop growth. Because many plants use as much of 0.2 inch of water per day, both plots could be out of water in two to three days.
The greatest benefit of the paper mulch was a reduction in weeds. The plot required little attention other than watering.
The moisture-holding capacity of the plot with the top soil was 25 to 35 per cent greater than the native soil -- a three-to-four day supply.
In the leaf-mold plot the organic matter allowed nearly two inches of water to be held in the upper six inches. Almost a seven-day supply, 1.3 inches, was available to plants. All crops on this plot resisted wilting two to three days longer after watering or rainfall than the crops in the other plots.
However, this increased moisture-holding capacity created a problem in early May during a period of wet, cool weather when deeply planted bean and squash seeds rotted and had to be replaced. Small, shallowly planted seeds did not rot. All seeds germinated well on the other plots.
At times, tomato plants on the paper-mulched and untreated plots were affected by droughty conditions, and blossom-end rot damaged tomato fruit on both plots. This damage is caused by an imbalance between the water needs of the plant and the supplying power of the soil. The greater available moisture in the leaf-mold and top soil plots prevented this damage.
The leaf-mold plot produced consistantly higher yields. Pepper and onion harvests were 140 per cent more than on the untreated plot. The yield of carrots, lettuce, eggplant and tomatoes was 25 to 45 per cent higher on the leaf mold plot.
Based on the cost of produce at local food stores at the time or harvest, $5,700 to $7,600 worth of food was grown on the 76 plots of the three-quarter acre inner-city site.
As a result of the experiments, the City of New Haven is composting 750 cubic yards of leaves, which will be spread on the garden plots in the summer to help increase yields.
"It is clear that the potential of a vacant lot is greater than it first appears to a scientist who is used to farming suburban soil," says Hill. A piece of land, a group of people with gardening zeal, leaf-mold to help increase yields, and a little technical assistance is all that is needed to turn a vacant lot into a flourishing garden."