Foliage Spray Boosts Your Garden’s Health and Productivity

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Gardener's Supply Co.: The professional Garden Sprayer.
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Plant uptake of nutrients can be 100% to 900% more effective when the foods are applied to leaves rather than to soil.
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Smith & Hawken: The Berthoud Sprayer.

Nutrient leaf foliage spray can boost you garden’s health and productivity.
Experiment: You’ll see the difference in your crops yourself!

Foliage Spray Boosts Your Garden’s Health and Productivity

Roots are leaves in the ground, and leaves are roots in the air.
–Alan Chadwick

As I wind my way down to our California hillside garden, I stop for a moment and examine a gray strand of Spanish moss that hangs from an oak branch over the path. This strange growth is not really a moss, nor is it a parasite leeching off its woody host. Instead, it’s a plant without roots; one that feeds solely by absorbing nutrients dissolved in fog or rainwater through its clusters of threadlike stems.

Of course, our normal house and garden plants do have well-developed root systems for gathering nutrients from soil. Yet, like Spanish moss, they also have the capacity to feed through above ground surfaces. Stems, buds, twigs and, most especially, leaves will readily absorb nutrients that are applied in a solution. So, in a real sense, leaves are roots in the air.

Foliar feeding is the practice of applying liquid fertilizers to plant leaves. This relatively new idea is fast becoming widespread. I recently worked at an organic research garden and minifarm. We relied on the soil’s microbial activity to supply crop nutrients, but that process was slowed by the area’s long, cool springs. So we began foliage spray feeding to stimulate plant growth early in the growing season.

The technique has many other applications. Some market gardeners now spray nutrients on fruit-setting crops like tomatoes and cucumbers to increase yields and on such leafy greens as lettuce and spinach to speed maturity and increase storage life. European grape growers use foliar feeds in their vineyards, and Chinese farmers similarly treat heading grain crops to increase yields. In our country, turf managers spray golf courses to help grass green rapidly, and some large commercial farmers use foliar feeds to prevent frost and drought damage. Other farmers spray regularly with liquid kelp to reduce aphid and red spider mite attacks or to control botrytis on strawberries and powdery mildew on rutabagas.

Fast Action

Leaves are green factories where the complex chemical processes of photosynthesis produce the compounds plants need for growth. Foliar fertilizers are absorbed right at the site where they will be used, so they are quite fast acting. Some gardeners have actually seen plants improve within an hour of spraying.

Leaf sprays are also highly efficient fertilizers. Agricultural scientist S.H. Witter pioneered some of the first scientific studies into nonroot plant feeding in the early 1950s at Michigan State University. He found that the uptake of various plant foods was from 100% to 900% more effective when the nutrients were applied to the leaves instead of to the soil. Much soil fertilizer may never get used by plants. Water-soluble nutrients like nitrogen often wash out of the earth. (As much as 50% of the chemical nitrogen fertilizer used in this country leaches into our waterways–creating a complex of environmental problems.) Other nutrients may, through chemical reactions, be bound into a form unavailable to plants. For instance, 80% of the phosphorus applied through conventional fertilizers may get locked up in the soil. On the other hand, up to 80% of foliar-added phosphorus can be directly absorbed by the plants.

Don’t Forsake the Gardening Basics

Before you rush out and put your garden on a daily leaf spray schedule, stop and remember the basic tenet of organic agriculture: Feed the soil, not the plant. Many feel that the biggest mistake of modern chemical agriculture has been its lack of focus on the sustainable base of all the earth’s production–the soil.

A healthy soil ecosystem rich in life and organic matter will help prevent nutrient loss due to leaching and chemical binding. It will even hold excess nutrients in storage until they are needed. For example, vesiculararbuscular mycorrhizae, fungi present in healthy live soil, increase the uptake of many nutrients, including phosphorus, and stimulate the growth of other beneficial soil microorganisms (such as nitrogen-fixing bacteria).

Fertilizers do not create fertility; building the soil does. In the long run, adding balanced, aged organic matter to your soil is the most efficient way to improve a garden. Foliar feeding, then, is best used as a supplement–a temporary or special procedure to boost production or help plants in a difficult growing situation.

The Trace Mineral Difference

The supplemental role of foliar fertilizers helps explain why many leaf sprays are so low in the standard nitrogen-phosphorus-potassium (NPK) elements that make up conventional chemical fertilizers. Some skeptics feel anything so low in NPK can’t do any good, but proponents, like Lee Fryer of Food and Earth Services, argue that the variety of micronutrients in such foliar sprays is exactly what makes them effective.

Plants use some 50 mineral substances. Most are required in very minute quantities, yet a lack of any of these will have a profound impact on growth. As Liebig’s Law of the Minimum–a basic principle of plant science–points out, the nutrient in least supply is the one that limits plant growth.

Ocean products like seaweed, kelp and fish are common components of foliar fertilizers because they’re rich in micronutrients. These sea products also contain hormones and amino acids (cytokinins and betaines) that play essential parts in the plant growth process–they’re involved in cell division, as well as chlorophyll and protein production. Betaines are particularly useful in reducing plant stress during drought and in providing some resistance against marginal frosts.

When to Use Foliar Fertilizers

Enough theory–let’s get to applications. Wait until young plants have enough leaf surface to absorb a spray well before you apply any foliar feed. Plants absorb foliar nutrients best in the early morning or late afternoon. Cloudy days are also good, but not if rain is imminent–it would wash the spray off the leaves. At what stage of growth should you spray? You can experiment with feeding at different stages, but the following are the ones most often recommended: during transplanting, flowering, fruit set and drought and cold periods, when sidedressing is normally recommended.

Here are some suggested guidelines for specific crops:

Leafy greens like lettuce or spinach: One application at transplanting, one (or two) three weeks later and one in the crop’s final week of growth.

Vining crops like melons or squash: Several applications when the vines start to run and the blossoms start to set, then one or two applications when the fruits are reaching full size.

Long-season fruiting crops like tomatoes, cucumbers, peppers and okra: One application at the first blossom set and then every 10 days or so during harvest.

Grains like wheat, corn, rye or rice: One application when the plant is 10 inches high and one or two when the heads or ears start to form.

Foliar Feed Recipes

The first foliar sprays we used at our California research garden were made from weeds. Like sea products, weeds are rich in mineral nutrients. The “water composting” preparation process completely kills weeds and their seeds (even ones that might survive normal heat composting). Besides, turning a garden invader into a crop booster provides a pleasing irony.

To make foliar weed spray, fill a 30- to 50-gallon barrel with weeds and water, in a ratio of one pound of weeds to three or four gallons of water. After two or three weeks, the solution will be ready to use. Pour out as much as you need, filtering the liquid well so it won’t clog your sprayer. Then thoroughly wet your crop leaves. One gallon of the weed feed should treat approximately 100 square feet of plants.

You can add more water and weeds to keep the barrel filled. Or do the same process on a smaller, more concentrated scale with a five-gallon bucket. Pack the bucket with weeds and cover them with water. After a few weeks, filter out the liquid and dilute it by five to 10 times with water, and spray.

Seaweed and other foliar spray solutions are available from several garden companies. But to make your own, here are some other possibilities. Age, strain and use these just as you would foliar weed spray. Many of these brews give off a strong odor while they’re steeping. If that happens, float a layer of peat or straw on top to absorb the smell. Experiment with your own recipes, but remember that foliar feeds are always used in more dilute amounts than liquid soil fertilizers.

Compost spray: Combine one part mature compost with two parts water (by volume).

Rodale’s manure tea: Mix two cubic feet of manure with 60 gallons of water.

Lee Fryer’s basic spray: Combine ¼ pound of seaweed meal and ¾ pound offish meal with five gallons of water. Ferment one month, and dilute this five to 10 times before using.

Henry Doubleday’s skipper tea: Steep 10 pounds of kitchen waste in 10 gallons of water.

Rich weed spray: Soak 20 pounds of wilted comfrey, nettle or thistle in 20 gallons of water. Ferment one month. This very rich fertilizer should have close to the same NPK concentration as a commercial 10-10-10 fertilizer. For foliar use, dilute it five to 10 times with water.

Seafood spray: Place scrap fish in a barrel, barely cover with water, and let ferment for two or three months. Skim off the top layer of oil (compost the leavings), and use it diluted with water in a 1:80 ratio. You can store unused oil in a closed container.

Prove It

Experiment for yourself. Regularly spray the leaves of part of a crop, but be sure to leave an untreated portion of that same crop as a control. That way you can honestly assess the effects of your foliar application. After all, foliar feeding is another task to add to that long list of gardening chores. If you spray nutrients only because this article recommends it, your enthusiasm for the job may diminish as soon as your recollection of these words does. But if you really see the difference in crops yourself, the noticeable improvement might guarantee foliar feeding a permanent place in your gardener’s heart.

Peter Donelan was a one-year gardening apprentice with John Jeavons’s Ecology Action of the Midpeninsula (Willits, CA). Jeavons is trying to help solve world hunger by developing gardening techniques for raising maximum food in minimal space. (His current indications are that a gardener may grow 322 pounds of food in six months on as little as 100 square feet.) Donelan is now teaching agricultural literacy at Stanford University.

Foliar Feed Sprayers

A recycled (and thoroughly washed) window-cleaner bottle may be adequate for spraying houseplants, a small bed of herbs or an experimental half-row of tomatoes. But if you’re going to foliar feed a full garden, you’ll soon wish for a more sizable sprayer, one you can pressurize with a few pump strokes so it will mist continuously. MOTHER offered a design for a homebuilt two-liter sprayer back in issue 80. In addition, here are a few companies that offer sprayers (write for free catalogues):

Gardener’s Supply
Burlington, VT

A.M. Leonard
Piqua, OH

Pinetree Garden Seeds
New Gloucester, ME

Smith & Hawken
Mill Valley, CA

Stern’s Miracle-Gro
Port Washington, NY