Tag Archives: soil test

Common Nutrient Deficiencies in Plants

Spotting nutrient deficiencies in your plants can be challenging, especially if you’re new to gardening. Here are what a few common deficiencies look like and how to correct them.

Soil Nutrients

Nutrients in the soil can be divided into two categories macronutrients and micronutrients/trace minerals.

The first category, macronutrients, comprises primary nutrients nitrogen, phosphorus, and potassium and secondary nutrients sulfur, magnesium, and calcium. If you think your plant has a nutrient deficiency, these are the likely culprits.

The second category, known as micronutrients or trace minerals, includes boron, chlorine, copper, iron, manganese, molybdenum, and zinc. While these are still important to plant health, they’re needed in such small quantities that it’s less likely your plant is deficient in one of these micronutrients.

You can read more detailed descriptions of what all of these nutrients do in our post, Understanding Soil Tests.

Nitrogen Deficiency

A nitrogen-deficient plant will grow slowly and lack vigor. The leaves may turn pale and yellow before dropping off, with the oldest leaves dropping first.

Note that it’s easy to overdo it when adding nitrogen, especially if you’re using chemical fertilizer. Adding too much nitrogen will cause lush, dark green foliar growth at the expense of fruit and flower production.

There are many ways to add nitrogen to your soil. While you shouldn’t directly apply it to plants, animal manure is a good choice if you have access to it. Compost will also add some nitrogen, or you can add seaweed or kelp meal, fish emulsion, bone meal, coffee grounds, soybean meal, or cottonseed meal. Using legume cover crops also helps to increase your soil’s nitrogen levels.

Phosphorus Deficiency

A plant that is deficient in phosphorus will also lack vigor and may be stunted. It might drop fruit before it’s ripe or not produce fruit at all. The lower leaves may appear red or purple.

You can add phosphorus to your soil using rock phosphate, greensand, compost, or bonemeal.

Potassium Deficiency

Potassium deficiency will probably be most apparent in your plant’s leaves, which may be mottled or curled or have brown edges. The plants will also be weak and have stunted root growth. They will likely be more susceptible to disease and pest issues.

Good potassium sources include manure, compost, seaweed or kelp meal, potash, granite dust, greensand, and wood ashes.

Sulfur Deficiency

While sulfur is a macronutrient, a sulfur deficiency is much less common. Signs include stunted growth and pale, yellow leaves.

Add sulfur with gypsum, compost, or sulfur.

Magnesium Deficiency

If your plant is deficient in magnesium, you may notice poor flower and fruit production, stunted growth, and dropping leaves. Leaves may also appear mottled with yellow/white patches or purple/brown patches between the leaf veins.

To correct a magnesium deficiency, add limestone, manure, compost, or greensand.

Calcium Deficiency

Calcium deficient plants may die back or have buds that die. Their leaves will likely appear burnt, curling, or have necrotic leaf margins. You may also notice issues like blossom end rot and other signs of tissue necrosis.

Use oyster shells, eggshells, limestone, gypsum, or fishmeal to add calcium to your soil.

Notice how similar a lot of these symptoms are?

If you’re having problems with nutrient deficiencies, the best advice is always to get your soil tested. It isn’t complicated or expensive and will tell you precisely what you need.

It will also tell you what your soil’s pH is. Soil pH can affect plants’ nutrient uptake and may cause deficiencies even if your soil is otherwise fine.

If your soil test comes out fine, your plants may be struggling due to over or underwatering or disease issues.

How do I prevent deficiencies?

The first step you should take is to develop a garden rotation plan that includes cover crops. They’re excellent for preventing erosion and adding nutrients to your soil.

Yearly applications of good quality compost can provide a wide range of nutrients to your soil.

Thinking like a plant

Books-Vegetable gardening in the Southeast-smallGarden Primer bookBarbara Damrosch states, early in her 633-page Garden Primer book, that “Good gardening is very simple, really.  You just have to learn to think like a plant.”

One of the challenges of learning to think like a plant is that not all plants think alike.

When you’re wondering how best to take care of a particular crop, the first question you’ll ask yourself might be “Where can I find good instructions?”  You might, for example, start by looking at the cultural notes in our catalog, or by looking in the “Edibles A to Z” section of Ira Wallace’s book Vegetable Gardening in the Southeast, or Barbara’s Garden Primer.

Another question to ask yourself is, “What do I know about the needs and habits of this plant’s relatives?”  Plants tend to be similar to their relatives in terms of the conditions they need for germination or fruit set, the relationships they form with soil microbes, the strategies they use to spread their seed, and many other factors.

For example, if you know that luffas are related to pumpkins and cucumbers, you can guess that growing luffas will be more similar to growing pumpkins or cucumbers than to growing tomatoes.

photos mid fall 2011 177 luffa stages
Left to right, the progression of luffas from flower bud to mature fruit: buds, flower, baby fruit with spent petals still attached, edible young fruits, intermediate-maturity fruits, and mature fruits for retting and use as sponges.

Luffas (also called loofahs), like most crops in the squash (cucurbit) family:

  • prefer dryer soil than most other plants, particularly while seeds are germinating
  • have delicate root systems, but can be transplanted with care
  • can sprawl or climb
  • use tendrils to cling to surrounding plants or structures
  • have flowers that are very attractive to bees
  • have separate male flowers and female flowers on androgynous plants
  • are easily killed by frost

If I was sending a soil test to a lab and wanted a recommendation on whether to amend the soil before planting luffas, I’d check the box of another crop in their family (assuming luffas aren’t on the list).  If I was worried that an insect might be attacking my luffa crop, I’d run through a mental list of the insects that I’ve known to attack other crops in its family. If I wanted to make a guess at which nutrients are abundant in luffas (when picked small for eating), I’d start by looking up which nutrients are abundant in other cucurbits that are also harvested before the seeds mature, like cucumbers or summer squash.  If I wanted to  harvest pure, market-worthy seeds from one variety of luffa, I’d plant it at least 1/2 mile from any other varieties of the same species of luffa, based on the similar isolation distances recommended for harvesting reliably pure seeds of other cucurbits.

However, any plant will have some significant differences from its relatives.  For example, most cucurbits set their seeds in a wet environment, but luffas set their seed in a dry environment.  Thus the techniques we use to clean luffa seeds are very different from those we use for most seeds in the cucurbit family.

It might be tempting to focus your gardening efforts on one family, grow lots of its members, and really learn how they think.  But diversity of plant families in your garden is one aspect of agrobiodiversity, and will help ensure that the bugs or diseases that like one of your crops won’t like too many of your crops.  It’s also important to rotate your crops, and like many farmers and gardeners, we organize our crop rotation according to plant family.

For an easy way to learn which plants are in which families, take a look at our illustrated list of the predominant plant families in American gardens.

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