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April Master Gardener Column

It’s April and soon we will be confronted with the questions of fertilizing. How much? When? What kind? How to apply it? Looking at the fertilizer section in stores selling plants just adds to the confusion. There are so many “designer” fertilizers for sale labeled for specific plants. Examples are rose food, tomato food, rhododendron food, etc. It doesn’t have to be that hard.

First, some general information. You can apply it to the surface of the soil or lightly scratched into the top inch. Rain, time, and earthworms will do the rest. No rain? Simply water your plants until the ground is moist, about an inch per week.

The directions for synthetic fertilizers call for multiple applications during the growing season because they are too potent to apply all at once. They will burn the plant. They also dissolve quickly in the soil and the excess washes away causing environmental problems downstream, so please follow the package directions precisely.

“Slow-release” or “controlled release” synthetic fertilizer may be a better choice. They control how fast the nutrients are released and can usually be applied once per season.

Organic fertilizer comes from things like plants, animals, or natural minerals. Apply them once per season. They work in one of two ways. Some are slow to dissolve in water, while others are eaten by microorganisms in the soil that convert the nutrients into a form useable by plants.

Organic fertilizer comes as pellets or some type of meal made from seeds. Two examples are soybean meal and cottonseed meal; however, the pellets are easier to apply.

Some gardeners prefer using purchased or homemade compost. It is a slow release, but the nutrient level is so low it is not legally a fertilizer. It does do great things for the soil and the beneficial organisms dwelling there. In my own experience, homemade compost made with manure as one of the ingredients had a stronger fertilizing effect than batches without.

Annuals require more fertilizer than perennials. Perennials require more than shrubs or trees. Container grown plants require much more fertilizer than in-ground plants. During the highest heat of summer, and towards the end of summer when the container plants are at their largest, they will need water daily. Fertilizer gets used quite fast and the potting medium doesn’t contain all the nutrients found in actual soil.

Finally, stay away from social media household product ideas as substitute fertilizer. Please don’t use Epsom salts as a fertilizer unless a soil test shows your garden is deficient in magnesium.

The Master Gardeners of University of Illinois Extension are happy to answer your gardening questions via email.  Send your questions to For additional resources, visit our website at