Foliar fertilizer is a fertilizer product which is designed to be applied directly to the leaves of a plant. A number of companies manufacture a range of foliar fertilizers, from organic products safe for use on food crops to more aggressive chemical fertilizers for ornamentals. There are a number of advantages to using a foliar fertilizer which make such fertilizers popular for some gardening applications.
With foliar feeding, as it is known, the nutrients are absorbed directly through the leaves of the plant. They work their way down the roots, but they also stimulate activity in the leaves, which in turn stimulates root development, because the plant starts to demand more water. Applying foliar fertilizer can increase uptake of nutrients from the soil by encouraging plants to take up more water, in addition to providing immediate benefits for a plant which may be suffering from deficiency.
A foliar fertilizer is not designed as an alternative to soil fertilizer and soil conditioning, but rather as a supplement which will increase efficiency and improve plant health. Uptake of nutrients from the soil can be very inefficient, and it can take several days for noticeable effects to occur. Foliar fertilizers act more quickly, and far more efficiently, as most of the fertilizer ends up in the plant, rather than in the soil.
There are some precautions which need to be observed when applying foliar fertilizer. It must be diluted before application to prevent fertilizer burn, and it also needs to be applied when plants are most likely to benefit. The best time to do this is when temperatures are cool and some dew is present on the leaves, as in the evening and early morning, as the stoma on the leaves will be open and able to absorb the nutrients. Applying during the heat of the day is inefficient, and can in fact damage the plant.
When selecting foliar fertilizer, it is important to think about the nutritional needs of the plant. Not all plants are alike, and a fertilizer formulated for one species may not be appropriate for another. Some fertilizers specifically list some examples of plants they are suitable for, and all should disclose their ingredients, allowing gardeners to determine how they should best be used. If a gardener is not sure about which product would be best, the staff at a nursery should be able to make some product recommendations.