JoAnne Skelly: Does foliar fertilization work?

Many people feed their plants using a hose-end sprayer. We see advertisements for water-soluble fertilizers in every gardening magazine and on TV. They claim immediate results, larger blooms, longer bloom times, increased veggie production, increased cold and heat tolerance and increased pest and disease resistance. Are fertilizers sprayed on the leaves more effective than those applied to the soil?

According to Dr. Linda Chalker-Scott of Washington State University, “materials applied to the leaf do not necessarily travel throughout the entire plant as effectively as they do through root uptake.” Foliar applied fertilizers stay in or near the leaves on which they were applied.

Foliar applications of certain nutrients, such as iron and manganese, can be useful for crops in alkaline soils. Foliar applications can supply small amounts of other micronutrients, such as zinc, copper and magnesium, which can help alleviate deficiencies in fruits. However, these applications don’t help the trunk or roots and don’t improve soil imbalances. They are merely a temporary solution in tree fruit production. A gardener needs to resolve the soil issues for long-term overall plant benefits.

I’ve written about the nutrients nitrogen (N), phosphorus (P) and potassium (K), which a plant needs in higher quantities than the micronutrients mentioned above. Leaves can’t absorb as much of these nutrients as a plant needs. They should be applied to the soil.

If N, P or K is applied to leaves in high enough quantities to benefit the entire plant, the leaves will be burned by the salts that make up the fertilizer.

Plants in our arid environment have thick “skins” (cuticles) on their leaves to protect them from dehydration. Fertilizers sprayed on the leaves may not penetrate to the growing points in the leaves due to the thickness of the cuticle.

The best way to grow thriving plants is to have a soil rich in organic matter and mineral nutrients. Feed the soil, not the plant. An alternative is to select only plants adapted to your soil type. Foliar feeding is not the best way to feed plants for good root, trunk or canopy growth. It can supply micronutrients to leaves and fruit, so may be helpful in improving micronutrient deficiencies in fruit trees. Applying fertilizer through the leaves is more expensive than soil applied fertilizers. If applied improperly, plants can be burned by foliar fertilizers.

Cooperative Extension’s free Grow Your Own classes are back. “Designing a Water-Efficient Landscape” will be presented at 6 p.m. Sept. 9 at 2621 Northgate Lane, Suite 12. Call 775-887-2252 for more information.

JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at skellyj@unce.unr.edu or 887-2252.