Gardening in containers: plant food

Learn how to meet the nutritional needs of your plants.

Photo Credit: Tomislav Stajduhar
By Angela McKendree

Every plant needs food and it is especially important that plants grown in containers, rather than in the earth, get fertilized often enough. But what many people don’t know is what kind of fertilizer to feed to their plants, or that there is even a difference between major fertilizer types at all. All fertilizer is not created equal. Luckily, your plant will communicate with you about what type of fertilizer it needs. That’s right, it will communicate with you; your plant may not verbalize, but if you stop and take a look at it, you should be able to read signs of nutrient deficiency pretty easily.

Here are some things to look for when trying to determine what your plant needs.

Signs of calcium deficiency

You can tell if your plant is calcium deficient if the veins in the leaves turn brown, the stems break, and the flowers (or fruits) deform and discolor. The discoloring is obvious on most fruits, such as the appearance of brown spots on apples.

Signs of magnesium deficiency

Chlorosis is a condition in which the tissue of the leaves turns yellow due to a lack of chlorophyll, the important substance that makes plants green. Older leaves will turn yellow first, then they will drop off and die. The newest leaves are the last to be affected. If not treated with the proper fertilizer, all of the leaves will turn yellow.

Signs of nitrogen and sulphur deficiency

Most plants need plenty of nitrogen, as nitrogen is a component of chlorophyll and chlorophyll is what makes plants green. Without it plants cannot photosynthesize. Signs of nitrogen deficiency are: older leaves are a lighter color than new leaves and the plant’s growth slows noticeably. The plant will show signs very similar to this if it is suffering from a sulfur deficiency.

Signs of phosphorus deficiency

The first signs of phosphorus deficiency will appear on the plant’s older leaves. The old leaves on the plant will turn dark green on the top side and red on the bottom side. The stem will probably also turn red. You will also notice slowed growth and the production of flowers will noticeably slow down. If the problem is not fixed with the proper fertilizer, the newer leaves will fall victim to the same discoloration in time.

Signs of Potassium deficiency

Potassium deficiency is a problem that will affect the plant’s ability to absorb water and grow new tissue. You will see the signs in your plant easily; the plant will wilt and die in areas that are stricken with the deficiency. The deficiency becomes a bigger problem when winter months are near, as the plant will also suffer a reduced resistance to frost.

The right fertilizer

Different fertilizers are designed to do different things. Study the symptoms of your plant to determine what nutrient your plant lacks. Then browse the fertilizer section of a nursery, reading the label to determine which one you need. Alternatively, you can ask an employee which kind of fertilizer addresses that need and they should be able to direct you toward one containing the nutrient you need.