Should we fertilize our garden plants, and if so, when and how?
If your soil has been well-tended by the addition of compost and mulches, there may be no need for supplemental fertilizer. This especially is true with ornamentals since you also can recycle the spent plant materials back into the soil providing all the necessary nutrients for the next growing season.
Deb Babcock's gardening column appears Thursdays in Steamboat Today.
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Even if you are growing and harvesting vegetables, you may not need to use fertilizers if you use compost, mulch and cover crops that add fertility back into the soil since harvesting takes away some of the soil nutrients. Growing cover crops such as buckwheat or winter oats, rye or clover and plowing them under helps put back nutrients into the soil.
Your shade trees, flowering trees and shrubs and even fruit trees generally do not need any supplemental fertilizer unless the growth rate is slower than normal (generally about 6 inches per year depending on species).
A soil test, conducted every three years, is the best way to determine the fertility of your garden soil and whether any fertilizer is needed. Tests can be conducted by soil testing labs across the country or at Colorado State University's Soil Testing Lab for a small fee (about $25). For details about getting your soil tested at CSU, call 970-491-5061 or bring a gallon bag of your soil into the local extension office and they will help you complete the paperwork and get it to CSU.
So if you do need to add some nutrients to your soil, here’s what you need to know:
Fertilizer will come in granular form, liquids and soluble powders, and as pellets or spikes. You can choose the form that is most convenient for you. Granular, pellets and spikes all release the nutrients slowly into the soil each time it rains or when you water your garden. Liquids and soluble powders soak into the soil and down to the root system faster but then will require repeated applications.
The label will show three numbers indicating the percentages of nitrogen (N), phosphorus (P) and potassium (K — the K is for kalium, the Latin and German word for potassium) in the container. (The numbers won’t add up to 100 percent because some type of filler is used that allows the nutrients to be applied in a convenient manner.)
Plants use NPK in a rough ratio of 3-1-2. Your soil test will provide you with information about exactly which nutrients are needed and how much you should use. Be sure to read the label carefully for application directions.
You do not need to buy different fertilizers for the different kinds of flowers, vegetables, shrubs and trees in your garden. Just pay attention to the soil test to make sure you add enough of the proper nutrient and not too much of other nutrients such as nitrogen, which can burn plant roots if used excessively.
So instead of automatically fertilizing your plants, consider the alternative of conditioning your soil with compost. Then mulch with grass clippings, bark chips, leaf mold, sphagnum peat, pine needles or inorganic mulches. If you do this every year, you'll lessen or eliminate the need for any additional fertilizer.
Deb Babcock is a master gardener through the CSU Extension Routt County. Call 970-879-0825 or email CSUMGProgram@co.routt.co.us with questions.