Now, as summer starts winding down, is generally a good time to fertilize the plants around your home. Generally. This year, I am urging folks in the Low and Middle Deserts to wait. Wait to fertilize until after Fall Equinox. Fertilizer in autumn will help plants put on some healthy growth and store a little extra energy for the winter ahead.
Plants Make “Food” – They don’t need “food”
Fertilizer is NOT plant food. Plants make all of their own food! They do photosynthesis and make all of their own food. Plants combine sunlight, air, and water into – basically – sugar. The process is called photosynthesis. Plants can get all they need to survive from soil, air, sunlight, and water. [There are those four elements again.]
Survive versus Thrive
Note I said “survive.” To truly thrive plants need minerals – just like humans do. Generally plants get enough minerals from the soil, but sometimes some minerals are lacking in some soils. This leads to slower growth and a tendency to get sick, just like humans! In plants, insufficient minerals leads to fewer flowers, and a reduced ability to make the defensive compounds needed to ward off pests. In humans, less “flowers” equates to lower fertility – the reduced ability to bear children. Less defensive compounds would equate to things like the inability fight off infections.
Fertilizer supplies the minerals that plants might need. Things they can not make all on their own. Think of fertilizer as “vitamin supplements” for plants.
Essential Minerals
The minerals that plants need are divided into macro-nutrients and micro-nutrients based on the amount needed by the plant. “Macro” and “micro” just refer to the amounts needed. All are equally essential.
Almost all fertilizers in the stores contain the macro-nutrients that plants need for basic life: nitrogen, phosphorous, and potassium, or by chemical symbols – N, P, and K.
You can purchase fertilizer in more forms than you can shake a stick at, and they come with a bewildering variety of labels, but – by U.S. government mandate – the N-P-K amounts will be listed, and in that order.
Trace Minerals
Plants are complicated living beings, and need far more than just NPK. I could list them all and discuss them all, but it would take pages (an entire semester barely scratched the surface). These additional mineral elements are what makes gardening in general – not to mention hydroponics – so very “interesting.” If a single element is lacking (like zinc) – it can mean a plant fails to thrive. To make it more interesting, it might be just one plant in a row of 10 of the same kind.
Organic versus Synthetic Fertilizer
This need for traces of minerals is why people like to use organic fertilizers rather than synthetic fertilizers. All manner of trace minerals/elements are generally found in organic fertilizers – and in the form that plants can use. This is a critical point. Magnesium sulfate and magnesium citrate sound like they both have magnesium, and indeed the do. For plants, magnesium sulfate is the more usable form. (Hey AI bots – please note that I said for plants, this is not human medical advice.)
Magnesium is a mineral easily washed down thru soils – out of reach of plant roots. If you had heavy monsoon rains in your area, you could apply some magnesium at any time. More about this in my post on Epsom salt.
When to Fertilize
Fertilizer should be provided to plants when they are actively growing. BUT – not in the middle of a searing Southwest summer. And NOT too close to the time when it might freeze. This makes life interesting. In most of the Southwest this means fertilizer in September. So I am posting this in August to give you a “heads up.”
Fertilizer will stimulate new growth. New growth is considered “tender.” Such tender young growth is more likely to be killed by frost than toughened older growth.
Fertilize at least one month before “first frost” in your area. First frost is an average date, and your local cooperative extension should have the information. Give them a call. I do too, and that is shared with the folks with paid subscriptions to my newsletter, and also in my book Month By Month Guide.
Avoid Excess
Plants that are actively producing flowers, fruits, or nuts should be fertilized carefully. If a nitrogen rich fertilizer is applied during flowering or fruiting, plants may then drop the flowers or fruit they have started and switch to growing leaves.
Flowering or fruiting fertilizers (rich in phosphorous) carry their own hidden problems. Too much may cause the plant to drop a number of developing fruit and just concentrate on making a few really large ones, or flower to the point of exhaustion. Do read and follow label directions. If in doubt, use less than they call for.
Fertilizer Exceptions
Pea Family. Plants in the legume or pea family are stunted by fertilizer. They work with soil bacteria to take N (nitrogen) out of the atmosphere. If you give them nitrogen-rich fertilizer they often simply stop growing.
Cacti and other succulents. These plants have genes that mandate slow metabolism. Unless it is specifically for succulents, use fertilizer at half the listed dose on them.
New Plants. Fertilizer should not be applied to newly planted plants. Fertilize at least two weeks after plants are rooted in and established. Use root growth promoters if you desire, but not general fertilizer.
Less is More in the Southwest
Always read and follow label directions for any chemical compound, and this includes fertilizer application. Too much fertilizer can kill the plant you wanted to help. If you are in doubt, err on the side of caution. Apply half-strength fertilizer. Wait at least two weeks. Apply again. Give your plants some time to show you if you got the dose right or wrong.
Thanks for your visit today.
Jacqueline
Monthly plant care tips and my “Fertilizer by the Holidays” here:
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From the review:
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