OVER-MULCHING; A PERENNIAL PROBLEM! (I)
By Bailey Walten 1993 Newsletter
Mulching, if done properly can be very beneficial to our trees and shrubs; but if done improperly, it can be deadly. The old adage, “too much of even a good thing is still too much”, is especially true with mulching. We often see properties where mulch is piled 8 – 10 inches or more around the trees and the shrubs look like they are half buried in it. This over-zealous use of mulch may keep the weeds down but it can also spell disaster to those landscape plants.
The benefits of mulching are well documented. It keeps roots cooler in the summer and warmer in the winter, suppresses weed germination and growth, protects from mowers and string trimmers, increases organic material in the soil which in turn improves the soil structure, water retention capability and nutrient availability. Soil compaction and evaporation are also reduced, and water filtration increases. However, these many advantages are quickly thrown out the door when mulch is applied too thickly and too often.
There are many different types of mulches. Usually organic mulches consisting of wood chips, shredded hardwood or conifer bark, or pine bark nuggets are used in the landscape because they are more attractive and provide nutrients to plants as they decompose. Well-composted mulches should be used to prevent having hot or sour mulch situation where shallow roots can be burned and pH can become dangerously low with high composting temperatures and toxic byproducts. Also to be avoided are trash mulches consisting of wood waste such as 2’X 4’s, pallets, and plain wood scraps which are almost pure cellulose with little nutritional value.
Hardwood mulches are 60-80% cellulose and break down much quicker than the softwood types which are primarily lignin. Lignin breaks down more slowly so pine bark mulch need not be applied as often. Problems arise when the application rate exceeds the decomposition rate and over time a wet, compact layer of bark fibers and insoluble, non-diffusible organic particles form a seal over the soil (often several inches thick) and prevents oxygen from penetrating to the plant roots. Shallow rooted plants such as azaleas, rhododendrons, andromedas, laurels, boxwoods, etc. are particularly prone to root suffocation due to over-mulching. Symptoms may include stunted growth, abnormally small leaves, chlorotic (yellowed) foliage, and die-back of major limbs. A wet, oxygen-starved root system is also prone to toot rot disease.
Another problem occurs when mulch is piled high around the base of trees such as cherry, linden, dogwood, and ash. Canker causing organisms can attack the lower trunk and girdle it as the bark softens and cracks.
There are several important rules to follow when organic mulching:
Always use mulch composted at least 60 to 90 days with good aerification.
Apply no more than 3 to 4 inches of mulch initially and scratch and turn it periodically to freshen the appearance and work it into the upper layers of soil.
Add more mulch only when needed (Fall is a good time to insulate roots before winter frost arrives). Hardwood mulch may need replenishing annually and pine bark mulch every 2 to 3 years.
The damage done by over-mulching does not show up overnight but occurs slowly and progressively over a period of years. By the time the symptoms appear, it is often too late to correct the problem. If you have too much mulch now, remove some of it and work the remainder. Good mulching practices can pay great dividends to your landscape. Start now and keep up the good work!!
PROPER MULCHING TECHNIQUE (II)
Mulching landscape plantings has beneficial effects, however improperly done it can be disastrous! The primary reason for mulching, from a homeowner’s viewpoint, is to suppress weeds and to look nice. Other than aesthetics mulch can also:
help retain moisture,
provide organic materials for nutrients,
insulate roots from freezing,
reduce mechanical damage to trunks.
There are a wide variety of materials available, some of them are very basic, while others provide a high-visual impact. Just about anything non-living could be used as mulch. Washed stone could be used in a modern setting for contrast while oyster shells at the beach will conform with that atmosphere. While these materials are unique they do very little for the plants environment. Preferably, the mulch you select will be a wood/natural product so that as it decomposes it will provide organic matter and nutrients to your plants. These materials will also hold moisture to aid the plants during drought periods.
Spring is the time to clean-up winter’s mess and get ready for the coming season, however, mulching is more beneficial when done in fall. In Oct.-Nov. before frost gets into the ground, you should apply a heavy layer of mulch to insulate roots from freezing as well as lock moisture into the soil. If this is done in early spring or winter while the soil is frozen you can actually reduce the growth of your plants by locking the cold in rather than keeping it out. In the spring you should remove (or spread) the mulch to half its depth. This procedure could work to your advantage as most landscape contractors will give better prices for fall work since their work load is not as heavy. Be careful not to allow the mulch to accumulate more than 3″-4″ before it has a chance to decompose. Too much mulch build-up around the base of the plant can cause rot problems as well as encourage an unwanted shallow root system. Very often we see mulch piled 6″-10″ or more around the base of a tree….this is improper and you are killing that tree.
For the most part mulches are designed to aesthetically enhance your landscape planting, however properly applied they will smother-out and reduce unwanted weed growth throughout the season. You can also reduce your man hours of maintenance and eliminate the need to do a lot of “trim” mowing be placing mulch around individual trees. You will also avoid doing permanent damage to their trunks and branches by pushing a mower or weedeater under them.
Most people use a shredded bark mulch, however there are many other alternatives depending on the effect you wish to achieve: Pine bark nuggets (large and small), Shredded hardwood bark, Cocoa shells, Pine needles, Wood chips (from tree trimmers), Decomposed leaf mulch, Peat moss, Stones, Shredded rubber. When selecting a mulch material pick the one that will blend best with your setting and still be beneficial for your plants. A good selection should provide organic matter, hold water and look nice.