Mulch Choices

Planting Techniques

MULCH CHOICES

Mulch is a critical ingredient in the organic program. It helps conserve moisture, buffers the soil from temperature extremes, shades out weeds, looks nice and increases the tilth of the soil. It also supplies food for soil life and nutrients for the soil, keeps raindrops from compacting the soil, keeps the sun from burning the humus out of the soil and prevents erosion.

After any planting - tree, shrub, groundcover, flower or vegetable - all bare soil should be covered with natural organic mulch. Mulch is not a soil amendment mixed into the soil - it’s a covering placed on top of the finished planting bed after the plants have been installed.

Not all mulches are created equal. There are many acceptable mulches, but they vary in quality and effectiveness. One of the best top-dressing mulches is partially decomposed compost. I discovered the benefit of this material at home as a result of being too impatient to wait on my own compost pile to finish its decomposition. The not-quite-finished compost has larger particles and does a good job of mulching and letting oxygen breathe through to the soil surface but carbon dioxide escapes out to be captured by the mulch.

Grass clippings should only be used as mulch if mixed with leaves and other debris. I don’t recommend lawn grass clippings as mulch by themselves because the flat blades plate and seal off the soil’s gas exchange. Grass clippings should be left on the lawn.

Straw and hay can be used if they are free of broadleaf herbicide residue. Alfalfa is the best hay mulch because of its nutrient value and the presence of triacontanol, a growth regulator.

Another excellent mulch is shredded hardwood bark. It is tree bark that has been run through a hammer mill. This smashing action gives the bark its fibrous texture, which helps to hold it in place in your beds even on slopes, but still allows air to circulate down to the soil. A less expensive and even better material is shredded native tree trimmings. It looks good and works beautifully. An added benefit of the tree trimmings mulch is that the buds, leaves, and cambium layers contain protein, which provides nitrogen and other nutrients.

Not all bark makes good top-dressing mulch. For example, the fine to medium grades of pine bark make, at best, second-rate mulch. Pine bark consists of flat pieces that plate together and seal off the oxygen from the soil. Pine bark often washes or blows away. The tars and resins in pine bark can also inhibit proper aerobic degradation. The only pine bark that makes decent mulch is the large, nugget size because it will at least stay in place well. The large nuggets don’t fit together tightly, so air can still circulate around the pieces down to the soil, and large pieces do not rob nitrogen from the soil as fine-particle mulch sometimes does. However, in general, I am not a big pine bark fan. It’s better than no mulch at all - but barely.

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Pine needles are a good choice when used as top-dressing mulch, especially when used in parts of the country where pine trees are growing. There’s also an economic advantage when the material is locally available and can be gathered from the forest floor, although care should be taken not to deplete the organic matter in any natural setting.

Walnut should not be used as mulch until fully composted. The raw material contains juglans that has strong growth-retarding properties.

Sawdust is sometimes used as mulch, but I don’t recommend it unless it has been mixed with coarser materials and composted for a while. Sawdust does make an excellent carbon ingredient for the compost pile.

Pecan shells make fair top-dressing mulch, but are much better if composted first with other vegetative materials. Pecan shells are not good to mix into the soil unless they have been composted first.

Shredded cypress makes lousy mulch. It tends to mat and seal off oxygen. It breaks down very slowly, and, contrary to popular opinion, that’s a problem. It’s an environmental problem to ship any mulch or compost material great distances. It’s also an environmental problem to harvest cypress tress from coastal areas.

I do not recommend the artificial mulches such as plastic or rubber fabric, nor do I recommend gravel as mulch. The non-organic mulches don’t biodegrade and don’t return anything to the soil. I also don’t recommend dyed and colored mulches. Natural mulches of organic matter will eliminate most weeding and cultivation, eliminate soil compaction, save money on irrigation, preserve and stimulate the soil microorganisms and earthworms, and maintain the ideal soil temperature. In the heat of summer, the soil surface under a proper layer of mulch will be around 82–85 degrees. The temperature of bare soil can be in excess of 120 degrees.

Some alleged experts say that whenever a highly carbonaceous mulch such as bark mulch is used, decomposition organisms will steal nitrogen from the soil unless a fertilizer is added that supplies one pound of nitrogen for each hundred pounds of mulch. Not true! For years, I have mulched with hay, bark, tree chips, etc., without supplying extra nitrogen and have never observed any symptoms of nitrogen deficiency as long as the mulch stays on top of the soil. When raw organic matter is tilled into the soil, there usually is nitrogen draft. Finished compost only should be tilled into the soil. People who still till peat moss and bark into the soil are behind the times. Conclusion: Use compost to prepare planting beds, and use a coarse-textured natural mulch on the surface of the soil after the plants have been installed.

Steel curbing Planting Techniques

Shredded native tree trimmings mulch Mounded bed

Mulches To Be Used After Planting. Planting beds should be raised, sloped down on the edge and covered with a thick blanket of mulch.

PROS AND CONS OF THE BASIC MULCH OPTIONS

Compost: Compost makes excellent mulch for annuals and perennials and for use as top-dressing mulch for newly planted young trees. A light layer of compost is also beneficial on new shrub and groundcover beds prior to the addition of the coarse mulch. Compost is magic! At least it contains nature’s magic. It is also effective to use around sick trees and other plants to help them recover. Compost is nature’s fertilizer. A thin layer of compost is the best choice for young seedlings of any kind.

Cypress: Shredded cypress mulch is not good mulch and shouldn’t be used. It’s long lasting but that isn’t a good thing. Mulch should break down relatively quickly to produce humus and organic acids to feed microorganisms. Harvesting cypress from coastal areas is an environmental mistake.

Hardwood Bark: Shredded hardwood bark is an excellent mulch material for ornamental planting beds. It is fibrous, has coarse and fine particles and grows fungi quickly. The microbes lock the material together to prevent washing and blowing, but still allow air transfer to the soil. Hardwood mulch is one of the best choices to use around newly planted trees, shrubs and other permanent plants. It’s also good for potted plants.

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Hay: Clean hay is good for vegetable gardens. Alfalfa is the best choice - Bermuda is the worst because of possible broadleaf herbicide contamination. Eight-to-ten-inch layers are needed to prevent weed seed germination.

Pine Bark: Pine bark is used widely as a mulch or for bed preparation material, but shouldn’t be. First of all, it won’t stay in place and has a strong tendency to wash and blow away. Very fine particles of mulch can sometimes rob some of the nitrogen from the soil. The large size deco bark is a fair mulch to use for shrubs and groundcovers. The large size of the deco bark allows air to flow around the large pieces and down to the soil and to the plants’ roots. Fine and medium size pine bark is not a good mulch choice. As pine bark breaks down, some rather nasty natural chemicals are released.

Pine Needles: Pine needles or pine straw make an excellent mulch to use in most planting beds, but they are certainly more appropriate when used in areas where pine trees grow, so they don’t look out of place. Pine needles are a much better choice than pine bark.

Shredded Native Tree Trimmings: These make excellent mulch to use around plants or as a natural groundcover. If ground into smaller texture, this mulch can be used on all types of plants. Because of the buds and cambium layer under the bark, this mulch contains more nitrogen than most mulches and, therefore, doesn’t take any nitrogen from the soil. Shredded trees and shrubs from your own property are my favorite of all mulches. This material, when partially composted or mixed with compost, is the very best mulch of all. These mulches are known as “living mulches”.

“Mulching by itself cannot make up for the shortfall of fertility in the soil” —Dr. William A. Albrecht

“But it can certainly take you in the right direction.” —Howard Garrett

Planting Techniques

ORGANIC MULCHES

Organic Mulches Rating Application Remarks

Pine bark (large size)

Pine bark

(small to medium) Fair 2–3” deep in Works well but some ornamental beds. people don’t like the look.

Bad Use as a last Washes and blows around. resort only. Contains harsh natural chemicals.

Cedar

Excellent Shredded cedar Cedar flakes are the is one of the best very best greenhouse mulches. flooring material.

Coffee grounds Poor Best to use in Slightly acid. Will blow and compost pile. wash away.

Compost

Excellent Use partially Save the more decomposed decomposed material to till directly in the soil. 1–3” thick.

Corncobs (ground) Poor Apply 3” thick. Availability may be a problem.

Cornstalks

Poor Apply 2–4” deep Coarse texture and not clean. if used.

Cottonseed hulls Fair Apply 3–4” deep. Have fertilizer value similar to cottonseed meal. Very light and tend to blow around.

Cypress

Poor Don’t use. Can seal off oxygen. Harvest is an environmental problem.

Lawn clippings Poor Better left on the Good source of nitrogen. lawn or mixed into Flat pieces plate and seal compost pile. off oxygen.

Leaves

Good Best if mowed or Blowing and washing can chipped before be a problem. applying 2” deep.

Manure

Fair Apply only after Fresh manure can burn composting. plants and can contain weed seeds.

Pecan shells, Good Apply 3” deep. Better Somewhat of a problem Peanut shells, to compost first staying in place. Rice hulls with other materials.

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Organic Mulches Rating Application Remarks

Peat moss

Terrible Don’t use; the worst Expensive, blows and mulch choice. washes away.

Pine needles Excellent Apply 3–5” thick Looks best when used in on vegetable gardens association with pine trees. and ornamental beds.

Sawdust

Poor Use in the compost Small pieces seal off oxygen pile, not as a mulch. exchange when used as a mulch. Blows around.

Seaweed

Straw, hay

Fair Not readily available Watch for salt content. but works well. Decomposes slowly.

Good Apply 4–5” deep Use for winter protection. in ornamental beds, Alfalfa is the best. Bermuda 8–10” deep in grass is the worst because vegetable garden. of possible chemical contamination.

Shredded hardwood bark

Excellent Apply 3–4” deep Best mulch of all for use in ornamental beds. on sloped areas.

Shredded native Excellent Apply 3–4” deep Even better when mixed tree trimmings in ornamental beds. with compost.

Gravel

Poor Best used at 3–4” Large stones and lava in utility areas. good for use in shady landscape areas.

Lava rock

Fair Apply 3–5” deep Avoid plastic sheets or fabrics under it.

Shredded native cedar

Excellent Apply 3–4” deep Use a thinner layer around around all plantings vegetables, small flowers and native plants.