Got any sickly plants in need of a fertilizer boost? If so, bypass the roots and spray soluble fertilizer on the leaves. Known as foliar feeding, this method has a number of benefits.
"The main advantage of foliar feeding is that nutrients enter the plant more quickly," said Christopher Totten, a certified ecological horticulturist for Oregon-based Whitney Farms, which produces organic fertilizers available in many Orange County nurseries.
"With foliar feeding, the nutrients can be absorbed into the leaf tissue within a day of application, which is faster than through the roots," he said.
You definitely save time in terms of uptake when you fertilize through the leaves, agreed Jim Kitano, manager of Kitano's Garden Center in La Palma.
"Apply fertilizer to the leaves and it affects the plant right away, whereas fertilizer added to the soil can take days, weeks or even a month to be absorbed," he said.
During winter, foliar feeding can be even more effective because in the cold soil, roots take up the fertilizer slower, experts said.
If your plants are already healthy, you're not going to see that much improvement, but the plants will benefit from the feeding. If you have a crisis situation, however, such as iron deficiency, you should see greening quickly. And in places where the soil pH is off, this may be the only way to get a response to fertilizer, said James Vlamis, a plant physiologist emeritus at UC Berkeley in the soil science department, who has performed numerous foliar feeding experiments.
"A plant can collect almost any micronutrient that is sprayed on its leaves," he said. "In the case of iron deficiency, we have applied fertilizer on the leaves and have had greening in four or five days."
Foliar feeding will quickly green up plants that have gotten a little yellow, said Paul Brecht, owner of Brecht Orchid Gardens in Costa Mesa, who foliar-feeds 1,000 containerized orchids at home.
Foliar feeding can also help prevent insect problems, he said. For instance, spider mites like it dry. Wet foliage will discourage them.
Feeding through the leaves is also effective on slope gardens, where applying granular fertilizers is difficult.
Experts warn, however, not to substitute foliar feeding for root feeding.
"Foliar feeding should be done in conjunction with proper soil maintenance," Totten said.
Added Vlamis: "Nothing beats the root system for taking things into a plant. Roots were created for feeding plants."
While there are foliar fertilizers on the market that contain a host of nutrients, Vlamis thinks the method is best used to apply micronutrients.
"Although I have heard of feeding macronutrients such as calcium, magnesium, phosphorus and potassium through the leaves, it is not the most efficient way to feed a plant," he said. "Plants need a great deal of these nutrients, and they can get more of them through the roots. In the case of micronutrients, such as iron, zinc and manganese, which plants need in small amounts, foliar feeding works very well."
In fact, for micronutrient deficiencies, foliar feeding is often more effective than fertilizing through the soil. Iron and other micronutrient deficiencies usually occur when soils aren't acidic enough to make nutrients available to plants, which is a common problem in Orange County soil.
"Our soils will bind up iron and not release it to the plants," Kitano said. "This problem is even worse in cooler temperatures."
Known as chlorosis, iron deficiency affects the color of new leaves. In minor cases, areas of yellow show up between the leaf veins, which remain a dark green. When the deficiency is severe, the entire leaf turns yellow.
Iron deficiency is especially common in plants, especially azaleas, that prefer a more acidic soil. Other plants that tend to show chlorosis are gardenias, hydrangeas, rhododendrons, citrus and camellias, but to a more limited extent.
Though foliar spraying can easily correct iron deficiency, experts also recommend decreasing alkalinity in the soil by frequently working in bagged or homemade compost and amending with gypsum or soil sulfur. Iron chelate, which holds iron in a form that can be absorbed by plants, can also be added to the soil.
There are a variety of foliar fertilizers on the market.
Organic gardeners can foliar feed with liquid fertilizers, including those containing liquid sea kelp and/or fish emulsion. Most water-soluble chemical fertilizers can be used too. Check the fertilizer package for instructions.
"If the fertilizer package doesn't say anything about foliar feeding, then ask a nursery person for assistance," Kitano said. "The product may be something that isn't intended for foliar feeding."
Also keep these tips in mind:
* Foliar feed early in the day so plants are dry by night. Hosing plants down in the evening isn't suggested because you can create fungus problems.
* When preparing a foliar fertilizer, follow package directions carefully. Applying too much fertilizer could burn the leaves of your plants.