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TIPS FOR MAKING THE MOST OF MULCH

Now that we know a bit about what to use as mulch, we need to learn how much, where, and when to mulch. I’ll make specific recommendations for mulching ornamental plants, vegetables, and fruits a little later. For now let’s start with some general tips for getting the most out of your mulch.

MULCHING 101

Don’t try to stretch your mulch too far. It’s like trying to paint with a dry brush. The end result isn’t worth much. Try to figure out beforehand how much mulch you are going to need. For a 100-square-foot garden, it will take about 1¼ to 1½ cubic yards of shredded bark, leaf mold, or gravel to make a mulch layer 4 inches deep. That’s eight to nine wheelbarrows full of mulch. You can’t have too much. It’s always good to have extra mulch on hand to replace any that’s washed away or decayed, or to cover a newly spaded area. Almost invariably you will end up using more than you thought you would. And you can always stockpile what’s not used right away.

The thickness of your mulch depends on the material you use. Usually the finer the material, the thinner the layer. Mulch depth can vary from ½ inch for small particles like coffee grounds to 12 inches for bulky stuff like coarse straw.

Remember that plant roots need to breathe. Air is one of the vital elements in any good soil structure; 50 percent air and 50 percent solid material is a healthy mix. Soil that is too compact has little or no air. One benefit of mulching, as you’ll recall, is that it prevents soil compaction.

Don’t mulch so deeply that you undo this good by suffocating your plants’ roots under too much or very compacted material. Let your soil breathe. Wet leaves that bond together and cake can be impenetrable. Fine mulches, unless they are applied sparingly, can compact and prevent air penetration too.

Replace old mulch that’s become decayed and compacted. Mulching promotes shallow root growth. Your plants can become like a spoiled child: Because the soil stays relatively moist beneath mulch, roots do not have to grow deep and work hard. They can stay near the surface. This means that once you start mulching, you are committed to maintaining it. If you change your mind and remove the mulch in midsummer, your plants may quickly turn crispy and die from lack of water.

Amount of Organic Material Needed to Cover a 100-Square-Foot Area

MULCHING BASICS

• Use material that won’t compress and smother the soil.

• Apply 2 to 4 inches over the root zone.

• NEVER allow any mulch to contact the plant stem.

Fluff mulch with your hands or a pitchfork once in a while so it doesn’t get too packed down. Break up the dry crust so water can filter through. If your mulch starts sprouting — perhaps because you have used oat straw or hay with lots of seeds or buckwheat hulls, which might contain a seed or two — flip the mulch upside down on top of the unwanted seedlings to choke them off.

CHOICES, CHOICES, CHOICES

Refresh or renew mulches in ornamental beds and around shrubs and trees. Using the same type of mulch in these plantings every season is fine, especially as you’ll probably just refresh what’s already there. To perk up tired-looking decorative mulch, sometimes just raking will bring larger, more colorful material to the surface. If that isn’t enough, you can add new mulch, but remember to remove as much as you replace. Keep the mulch layer 2 to 4 inches deep, no thicker for most mulches. (Ruth Stout’s hay and straw approach is the exception.)

Heaping new mulch on old isn’t a problem in itself. The danger is in overmulching — increasing 3 inches of wood chips to a 6-inch layer, for example. More is not better. Overmulching is likely to kill your plants, maybe not overnight but after a season or two.

Do not use the same mulch year after year in your vegetable garden. This advice is based on the same principle that it is not a good idea to plant the same crop in the same place year in and year out. A good mulching may last for several seasons. When finally it does decompose, it should be replaced by something else. Plants and soil seem to like variety the way you and I do.

Apply thicker mulches to sandy, gravelly soils and thinner mulches to heavy clay soil. Avoid mulching at all in low-lying spots — places that are sometimes likely to be “drowned” with water. Although it isn’t always necessary, you can remove mulch during a particularly rainy period, if you have time, to prevent the soil from becoming waterlogged.

Darker mulches like buckwheat hulls and walnut shells absorb heat and warm the soil beneath them. Lighter mulches, such as ground corncobs, reflect light and heat the soil less. Choose mulch color according to where you live and according to the heat-loving or hardiness characteristics of the plants you are mulching.

IT’S IN THE APPLICATION

Cultivate around your plant before applying mulch. This is important if they have been in the ground awhile without mulch. Loosening the surrounding soil and removing any weeds now will pay off later. Be sure to water the plants generously. Spray with kelp solution or spread fertilizer on the soil now, too. Top with the mulch layer, which will help keep the soil underneath moist.

After-the-fact mulching cannot do much good if the ground is dried and baked hard. This little bit of advance preparation shouldn’t be too much of a chore, knowing that you won’t have to do any more work there for the rest of the season once the mulch is in place.

Wait to apply your first mulch until after plants started from seed are pretty well established. Mulch between the rows first, not right on top of where the seeds were planted. You can begin to mulch the seedlings just as soon as they are an inch or two higher than the thickness of the mulch. Leave an unmulched area about 6 inches in diameter around each plant for about two weeks. Later, when the mulch is good and dry, bring it within 2 or 3 inches of the stems.

Heavy mulch is most effective if applied after a rain shower, when the ground is moist (but not soaked). If the ground is too dry to start with, it will tend to stay dry for the rest of the summer unless there is a real cloudburst.

Do not apply wet mulches, like spent hops or new grass clippings, on very hot days. Be sure that they do not touch plant stems. When the temperature is above 90°F, such mulches, when wet, tend to generate so much heat that they actually can kill plants they touch.

Peel off “books” or “flakes” (3- or 4-inch layers) of hay and place them between rows of vegetable plants. This will make a clean path for you to walk on during rainy days and will keep the weeds down. If any weeds come through in force, add more layers.

Books tend to be pretty dense because the hay is so tightly packed by the baling machine. Sometimes it is a good idea to loosen them by pulling the hay apart a little with your hands. This is an especially good idea if you are going to throw them on top of onions or potatoes that you want to grow up through the mulch.

In a rainy year, mound the mulch slightly to encourage some water to run off into the area between rows (A). If it is very dry, make a shallow furrow in the mulch along the row of plants (B). The indentation will tend to collect water, which will seep through the mulch to the plants.

THREE CHEERS FOR MICROBES AND WORMS

Bacteria and earthworms are strong allies for any gardener. Without help from lots of microbes in the ground, mulch would never decompose, and the vital elements that are tied up in organic matter would never be released. Worms predigest matter in the soil and liberate chemicals in their castings that plants can use for nourishment. They are also excellent indicators of how useful a material will be as a mulch.

Earthworms are affected by changes in season and temperature. They are least active during the hottest months and the coldest months. In the summer they can be coaxed into working harder if you keep enough mulch on the garden to keep the soil moist and cool. In the late fall, earthworms need to be protected from freezing. This is why I recommend mulching annual beds for winter before the ground is frozen hard.

TROUBLESHOOTING WITH ORGANIC MULCHES

Be alert for signs of nitrogen deficiency when you use some organic mulches, such as fresh sawdust, wood chips, ground corncobs, and some cereal straws. Bacteria that break down the mulch and turn it into humus require a large amount of nitrogen themselves, so they take nitrogen from the source most available to them: the soil. This, as I have already suggested, makes the plants look yellow and stunted because they are not getting enough nitrogen.

For plants in distress, an immediate spray or watering with kelp solution will help. Follow with an application of alfalfa meal or cottonseed meal scratched gently into soil around the plants. Or use your regular fertilizer as directed. Water well.

Mold can develop in too moist or shaded organic mulch material. To get rid of it, turn the mulch regularly. Mold does little harm. In fact, mold is evidence of a healthy decomposition process. It seems to offend the human eye more than it bothers soil or plants.

WHAT’S GROWING IN MY WOOD MULCH?

Wood and bark landscape mulches can be hosts to several fungi that may look strange but are natural and harmless. Fungi and bacteria are integral to decomposition; they break down wood and bark into humuslike material that plants thrive on.

For instance, mushrooms and toadstools, slime molds, and bird’s nest fungus are not harmful to landscape plants or people (unless eaten).

On the other hand, the artillery fungus (a.k.a. sphere thrower or cannon or shotgun fungus) is a real nuisance along the East Coast. An artillery fungus (Sphaerobolus stellatus) is so small that it’s easy to miss at first. Clustered, the fungi appear matted and gray or bleached. Up close, they resemble tiny cream or orange-brown cups holding wee black eggs.

Trouble comes during the two to three weeks when the fungi reproduce. When the light, heat, and moisture conditions are just right, they actually shoot these black eggs (sticky spore masses) at light-colored surfaces, such as a white house or bright car. Problem is, this “egg” is like a speck of tar. The sticky, brown and black spore masses are very difficult to remove without damaging the surface of the house or car. One or two spots aren’t so noticeable, but en masse they are an unsightly mess. Even if you get them off, the remaining stain requires repainting. In Pennsylvania, insurance companies routinely accept claims to repaint outdoor surfaces and replace the aluminum siding on buildings hit with artillery fungus. In 1999, these fungi caused more than $1,000,000 in damage in the state.

To date, there are no known controls for the artillery fungus. Pennsylvania State University researchers are studying the problem and possible solutions. The Connecticut Agricultural Experiment Station recommends avoidance and prevention. Rake wood chips and bark mulch to disturb the fungus and dry out the mulch. Periodically top off decaying mulch (which contains carbon the fungi use as food) with fresh mulch composed of 90 percent bark. Or replace wood-based mulch with other types, such as black plastic or stone, in areas adjacent to buildings and parking areas.

Mulches are excellent places for disease spores to overwinter and multiply. Remove and burn mulching material that you know has become disease infested. Don’t till it into the soil. To reduce disease possibilities, don’t make mulch from refuse of a plant being protected by mulch. In other words, although chopped pea vines might be an excellent feeding mulch, use them on something other than new pea plants.

TROUBLESHOOTING WITH PLASTIC MULCH

Disguise plastic mulch by covering it. If you recognize the advantages of plastic mulch but are offended by the sight of it in your garden, cheer up. Maybe you don’t have to look at it. The plastic (or asphalt paper, for that matter) can be buried under a thin layer of something else, like pine needles, crushed stone, wood chips, or hulls of some kind — even dirt!

Apply water-soluble fertilizer slits in the plastic. If plants under a plastic mulch show signs of needing side-dressing, dissolve fertilizer in irrigation water that is run through a hose toward the T-shaped slits in the plastic. The stem of the T should point toward the direction the water is coming from.

Be a creative as well as a practical mulcher. Experiment, read, and talk to your neighbors. Use your tiller and your chopper, if you have them — even your rotary lawn mower — to help you try out new materials and techniques that the “armchair experts” have not even thought of yet. It is everyday gardeners — sometimes only moderately experienced ones who are not yet set in their methods — who learn the most and can teach us much about gardening.