Our brief winter ends in late January when soil temperatures begin to warm to 55 degrees or above. Roots that were dormant during the 6 to 8 weeks of colder soil temperatures begin to grow again, requiring a shot of nutrients to energize them.
Recommendations for fertilizer types and application rates have changed greatly over the last decade. Current research from University of California ANR advises applying fertilizers that contain much less, even no nitrogen to growing plants. Nitrogen percentages are the first of three numbers that should be prominently displayed on any fertilizer label; the other two numbers indicate the percentages of phosphorus and potassium in that order. These recommendations are based on several factors including the high amounts of nitrogen from fertilizers that runs off into our water supplies and the discovery that excess nitrogen in the soil actually interferes with the ability of beneficial micro organisms and fungi to affix nitrogen to plants’ roots.
You may have stored several types of fertilizer for years in your garage. Before you head out to feed your trees and plants these next weeks, take a minute to check labels for percentages of nitrogen. Many fertilizer brands that have been consistently popular for decades have extremely high nitrogen percentages (15 to 30 per cent) that produce a quick flush of new green growth which many gardeners believe indicates a healthy vigorous plant.
In fact, slow steady growth as well as consistent productivity with good disease and pest insect resistance are the marks of a healthy plant. Providing just enough nitrogen in formulations that make it available to the roots over long periods of time results in very healthy plants and very healthy soil.
There’s no need to throw out those bags, bottles and boxes of higher nitrogen fertilizers-just cut back on application amounts and timing. If, for example, the label of your rose and flower fertilizer with 10 per cent nitrogen recommends applying a cup of fertilizer to each rosebush every two weeks, try applying a quarter cup once a month instead and observe the results. The most obvious signs of nitrogen deficiency are yellowing leaves showing green veining and reduced bud set and fewer new leaves. You can always increase the application amount slightly until any symptoms of nitrogen deficiency disappear.
Granular formulations dissolve slowly over several weeks and can be reapplied less frequently; liquid formulations leach out of the soil quickly, usually within two weeks. When applying high nitrogen liquid fertilizers, reduce amounts to at least half the recommended rate but continue to feed plants every two weeks until the supply is used up and can be replaced with a lower nitrogen granular type formulation.
Here some of the adjusted application rates for the first spring feeding.
Cool weather crops (lettuces, peas, broccoli, chard) and spring-blooming annuals (pansies, snapdragons, etc.): sprinkle a tablespoon of a lower nitrogen (5 per cent or less) granular fertilizer or a couple of tablespoons of compost at the base of each plant monthly.
Fruit and nut trees (except citrus): apply a cup of a lower nitrogen granular food twice a year-at bud break in spring and after harvest in fall.
Roses: dig in a cup of compost or a half cup of the lower nitrogen food monthly during the growing season.
Send Elinor Teague plant questions at firstname.lastname@example.org or email@example.com (“plants” in the subject line).