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You Can Skip the Fertilizer

Fall gardens want compost

It is highly unlikely your garden has used up all the fertilizer you applied this spring. This is especially true if your garden soil is rich in organic matter and you used lots of compost.
    Compost raises soil temperatures, while its organic matter releases nutrients at a rate nearly equivalent to the needs of plants. The roots from the previous crop are also decomposing and releasing nutrients.
    If you used your own compost or one based on yard debris, your plants will benefit from an application of nitrogen. But if you used compost from lobster waste or crab waste, you’ve almost certainly got all the nitrogen your fall crops will need.
    If you are an organic gardener, blood meal, cottonseed meal and fish emulsion are good sources of nitrogen. Other sources of nitrogen include calcium nitrate, ammonium sulfate, ammonium nitrate and urea. Don’t apply slow-release formulas on fall vegetable gardens.
    Fall gardening is an excellent time to maximize your use of compost. If you are tilling the soil to control weeds, incorporate compost into that surface layer of soil. With soil temperatures into the upper 70s, the compost will instantly start releasing nutrients at just the correct rate to promote good steady growth of plants. As the soil begins to cool in mid-September, the release rate of nutrients from the compost will decrease. At the same time, the nutrient requirements of maturing plants will be less. After soil temperatures drop into the 30s, the compost will stop releasing nutrients, thus reducing nutrients lost to leaching. As soon as soil warms in the spring, the organic matter in the compost will start releasing nutrients.
    Another advantage of applying compost in the fall is that spring garden tilling will incorporate the residual compost more deeply into the soil, where it will help reduce the bulk density of the soil and improve its structure.
    Organic matter does so much good for soils. In addition to providing nutrients and reducing the density of soil, compost also has disease suppression properties most effective when applied in late summer. Soil-borne diseases are most prevalent when soil temperatures are high. Applying compost to your garden soil in time for planting the fall crop helps maximize all of the benefits compost has to offer.
    Only where you’re planting carrots do you want to skip the compost. Carrots grown in composted soil will look like clusters of fingers. That’s because high levels of organic matter tend to cause multiple roots to develop on tap-rooted plants. I reported these findings from studies I conducted in the mid 1970s on the use of compost in the production of black walnut trees. This effect was beneficial for producing walnut seedlings for transplanting but not good for growing carrots, where a single root is preferred.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.