Gardening Tips: Elementary, My Dear Gardeners

Editor’s Note: We’re dipping into Michelle Smith’s archives to provide timely tips for gardeners.


What to do this week

This week, we continue with the soil nutrients I introduced last week. We are left with N, P and K. I would like to give you an idea of what you can expect to see in your plants if your soil is deficient in these elements, which should explain why now is the time to be augmenting the soil, before these symptoms arise.

Students testing soil fertility, circa 1816. (Source: By OSU Special Collections & Archives : Commons [No restrictions], via Wikimedia Commons)

Students testing soil fertility, circa 1816. (Source: Oregon State University Special Collections & Archives : Commons [No restrictions], via Wikimedia Commons)

If your soil is deficient in N, nitrogen, you are going to get stunted growth and pale or yellow leaves, starting with the older leaves. This kind of deficiency is especially noticeable during fruiting, because the plant needs a lot of energy to put into setting fruit. If your plants do not get enough nitrogen you will certainly notice.

Some plants — like squashes and lettuces and onions — are very heavy nitrogen users. They will really suffer if you have a nitrogen deficiency. But if you add too much nitrogen, your tomatoes will be disappointing. Tomato plants love nitrogen so much that they just keep growing more and more leaves and don’t bother to make tomatoes. Some of what you will learn to do with your soil does depend on what you are growing.

Phosphorus is the next element, represented by P. If your plants are not getting enough phosphorus, you are going to get purplish streaks on the underside of the leaves. The leaves will also be yellowish. You will get very poor flowering and poor fruiting. This will be particularly evident in cold or wet soil. Sometimes if you plant things outside too early you will notice this. In this case you, may not be low on phosphorus but in cold and wet soil the plants have a difficult time taking it up.

Finally, we have K, for potassium. If your soil is deficient in this mineral, lower leaves will be spotted or mottled or curled. The fruit will not mature properly, and the plants will have less resistance to disease.

So now you know why you should prepare and fertilize your soil in Spring. Organic sources of nitrogen include good compost, well-rotted manure or blood meal. Phosphorous is also found in manure. This element is the one that is most difficult to replace. If you are taking away plants and fruit from the land, for food, you are taking away phosphorous, and you have to replace it somehow. Good organic matter will help, but you often have to add phosphorous in addition to your compost. Bone meal is a good source.

These elements work in concert, and with the micro-organisms in your soil. For example, your plants excrete sugars from their roots which the micro-organisms feed on, and in exchange, they transform phosphorous into a form the plants can use more easily. This is why you want a good healthy soil with lots of life in it. But if you add a strong chemical nitrogen for fertilizer, it will kill these micro-organisms. This is another reason to go for natural sources when you fertilize your soil. You are working against yourself if you use artificial fertilizers, especially when it comes to phosphorous.

When it comes to potassium, some people use wood ash, but it is not a good solution. Wood ash is so alkaline it can shock the soil and damage the micro-organisms. Better sources of potassium are kelp, and seaweed in general.

If you are not feeling experienced enough to observe your garden and notice these deficiencies in time to act, you can get a soil test. It will tell you how much of each of these elements is in your soil, but it won’t tell you how much is bioavailable, or easily usable by your plants. It will give you a base line, though. It is important to do these soil tests properly. Don’t take soil just from the surface, or just from one spot. Do a good mix. You can get a soil testing kit from the Farmers Co-op on Keltic Drive.

As you learn to notice the symptoms I have listed, even mid-season, you can take quick-fix actions. It isn’t like lime, which I explained last week, has to be added with lots of advance time for it to work in. You do have to be careful though, and consult, and start to learn what your particular crops like and what they don’t like in abundance.

Fish fertilizer, mid-season, is good to use as you are developing your skills. It is mild, a good quick fix, but it isn’t a long-term solution. It is good for phosphorus and nitrogen, but in the long term you are going to develop the routine to amend your soil by working in your bone meal, top dressing with manure or compost, and giving the soil the time it needs. The time of year to do that is now. As the season develops, and when the time is right, I will talk more about short term fixes, like compost tea and fish fertilizer, and other tricks that will help you.

If this weather keeps up, we may soon be seeing weeds. Next week will be a good time to talk about what weeds tell you about your soil.


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Market gardener, farmer, workshop leader, seed-saver, political candidate and mother, Michelle Smith has spent over 30 years coping with the challenges of our bioregion and in the process has built a store of practical and technical knowledge. The Inverness resident has served on the board of Seeds of Diversity Canada and represented Alternative Producers with the Federation of Agriculture but can do nothing about her hair. She is pictured with a head of Club Wheat, a seed that shares her approach to hairdressing.



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This article was first published on 12 April 2017.