Fertilizer is not always needed for soil, but sometimes it is

We usually approach the garden season with heightened eagerness for our plant babies to do their best. How can we assist them, we ask ourselves? Fertilize is the usual answer, in the belief that we’re feeding them. We’re not. Plants get their nutrition mainly from sunlight, making their own food, but also some from mycorrhizae and other fungi and microbes in the soil, so we’re adding nutrients for them, essentially. If we’ve sited them in the proper place and watered them sufficiently, we’ve really done what is necessary for growth.

This is the time for patience and reflection. Do we want our plants to set numerous blossoms or fruit? That requires a different fertilizer emphasis than if you want luxuriant foliage.

Remember that foliage that is too luxuriant is especially inviting to destructive insects and disease.

We’re advised to test soil often, but that can be costly. Some of us depend on our plants to tell us what they need, since home soil test kits have a reputation of being unreliable. Good compost and a proper pH (that is, somewhere close to a pH of 7.0), correct sun exposure, good drainage and about one inch of water per week should produce healthy plants. If not, then fertilizer should be considered. I think home pH tests are reliable, and if your pH is off, your garden suffers.

Many soil tests do not test for trace elements, those less crucial than nitrogen, phosphorus and potassium. Oversupply of some elements such as calcium may block the plant’s uptake of crucial ingredients, and that may be discovered by having a lab test plant tissue. The best fertilizer advice is to be cautious, and adhere to the idea that more is NOT better. In most cases, LESS is better. For tests, you can get them through your county extension office of the University of Idaho, or from private labs. Ask for price and what information they’ll yield.

Your best bet at this time of year is to just use a layer of good compost on your garden bed. That may be all your plants need until they need a little boost when blooming or producing fruit.

If your garden doesn’t have distorted or discolored leaves or stalks, but just doesn’t look vigorous, consider using a foliar feed. I use one teaspoon of Epsom Salts dissolved in a pint sprayer of water and spray it on chile plant leaves that are paler than dark green. If plants don’t just look right, try a light strewing of alfalfa meal, kelp meal or a combination of trace elements such as Azomite. They all contain trace elements that aid growth, and alfalfa meal contains growth stimulants. too.

If you’re using a fertilizer made of synthetic materials, be extremely cautious, for those may be over-applied easily, “burning” your plants. Slow release organic fertilizers won’t burn your plants, but this should be applied in autumn, so it’s ready for spring growth. Do not use fresh manure on a garden bed. It should be composted, and organic gardening guidelines specify that if you use it, it should be at least 120 days before harvesting ground-contact edibles in that medium, 90 days before blueberries, etc. Fresh chicken manure may even “burn” your plants.

One of the best gardeners I know uses liquid fertilizers diluted so much you’d think it would make no difference, but it does. I’m fond of the Alaska fish fertilizers, especially one called MorBloom, that’s rated 0-10-10, the latter two numbers for phosphorus and potassium. I like to use that occasionally on “fruiting” crops such as chiles and tomatoes. The Alaska fish fertilizers, I think, result from commercial fishermen having been in too long a line for a tender, or some other reason they delay getting to a tender to process their catch. Better gardeners take advantage of the ensuing spoilage than to waste those fishy lives.

Trees don’t often need nutrients other than what’s already in our soil, but if you do choose to fertilize them, do that before they begin the very long process of shutting down for winter. That process starts here about June 15. Grapevines here are usually fertilized in June, if necessary. Mature grape vines shouldn’t need fertilizer, and excess nitrogen will cause foliar growth that may become so vigorous it invites destructive insects and disease, in addition to causing fruit loss. Those effects of over-fertilization are some to be taken seriously on any crop.

This story was originally published April 5, 2017 at 4:58 PM with the headline "Fertilizer is not always needed for soil, but sometimes it is."