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There is a lot of noise about fertilizer and plant food out there and it can be confusing.
We are here to demystify the idea of “feeding your plants”.
Do you need to fertilize?
Some plants are like Ben, they are born hungry. Take roses for example. They thrive on well-drained, rich soil and perform best when they are fertilized in spring.
Many other plants do not need fertilizer. If your soil is rich in natural nutrients, and it contains loads of microbes and organic matter, the chances are you won’t have to fertilize. Most of us do not have perfect soil, so the idea of fertilizing your hungry tomatoes, for instance, is a good one.
Every package of fertilizer sold in Canada has a three-number analysis printed on the package. The numbers always appear in the same order and express the percentage of each in the package: nitrogen, phosphorous and potash. These elements are of greatest demand by plants.
What do they mean?
Nitrogen (N): promotes green vegetative, leaf growth. A spring lawn fertilizer like 18-0-8 is designed to produce a fast green up. Some fertilizers contain an ingredient that slows the release of the nitrogen over a long period of time. Plant Prod produces a popular fertilizer for hanging baskets, 16-16-16 with controlled release plant food. Apply once and you are done for the season.
Phosphorous (P). Promotes root development and blossoms. Many fertilizer products for fruiting and flowering plants contain a high level of phosphorous. You will not find phosphorous in most lawn care products for environmental reasons: phosphorous or phosphates should not ever make their way into fresh water.
Potash (K): An enabler. Potash helps nitrogen and phosphorous do their job. Analysis has shown that this element is a general assist to all the elements that a plant requires to perform best.
N-P-K, listed above, are the elements in highest demand by plants but they are not the only ones needed to encourage plant health. Micro-nutrients like boron, magnesium (found in Epsom salts) and iron are just three of many. Each provides its own list of benefits and a deficiency of any one of them can create maladies in plant health. A soil test will tell you if your soil is lacking in one of them. Soil test kits are sold at most garden retailers.
Chemical or natural?
Truth is, plants do not know the source of these basic nutrients. The mantra of organic gardeners is, “if you feed the soil, it will feed the plants”. In other words, synthetic fertilizers (or “chemical” fertilizers) do nothing to enhance the character and value of soil. They merely sustain plant growth as the plant requirements demand it. If you only apply synthetic fertilizer to your lawn and garden plants, in time, the soil will be deficient in organic content that includes microbes, beneficial insects like earthworms and the micronutrients mentioned above.
We use copious quantities of compost each spring, to replace the natural ingredients in the soil. Mark has a six cubic yard composting bin in his 10-acre garden. Ben trucks in a pick-up load of aged compost each season to his allotment garden.
When to use fertilizer?
As a rule, we use fertilizer or “plant food” when a plant demands it.
Potted plants, including hanging baskets and window boxes, benefit from fertilizer as the soil mass that they grow in is limited, compared to those grown in the garden.
Lawns benefit from an early dose of quality lawn fertilizer, especially after a long, cold Canadian winter. Like a bear, grass plants crave the nitrogen and a dose of iron, which produces a very deep green. Some quality forms of iron can produce an almost “blue” green, like that of a golf green this time of year.
Plants with a low demand for fertilizer include most native plants, perennials and ornamental grasses.
Mark Cullen is an expert gardener, author, broadcaster, tree advocate and Member of the Order of Canada. His son Ben is a fourth-generation urban gardener and graduate of University of Guelph and Dalhousie University in Halifax. Follow them at markcullen.com, @markcullengardening, on Facebook and bi-weekly on Global TV’s National Morning Show.