By John C. Fech, UNL Extension Horticulture Educator, and ISA Certified Arborist
For many gardeners, applying mulch is standard procedure... like brushing your teeth. But before you jump the gun and mulch away,. it’s important to survey your landscape needs. Instead of merely tossing bark nuggets to and fro, ask yourself the question, “Why do I want to mulch this flower garden, this strawberry patch, this veggie garden?” Think about moisture retention, weed suppression, cooling or warming the soil, and of course, its appearance.
1. First of all, are there any mulches to avoid?
Don’t use grass clippings from a lawn that has been treated with a broadleaf herbicide in the last 3-4 weeks. Additionally, most horticulturists and arborists, myself included, turn up their noses at non-plant by-products. Yet, each mulch type has its place.
2. What type of mulch should I use?
There are 2 basic groups of products, organic mulch made of plant by-products, and inorganic. Plant by-products include the following:
- Grass clippings – great for short term situations such as veggie and herb gardens. They can cool the soil, suppress weeds, and best of all decompose over the summer. Later they can be tilled into the soil, increasing organic matter content and root expansion for future plantings.
- Wood chips – great all purpose material. Usually quite inexpensive, can easily be obtained by finding a tree trimming crew and trading them a 6 pack of their favorite beverage for a pickup truck load. Of course, you’ll usually get a Duke’s mixture of tree species, but the price is right.
- cypress/pine/cedar – these materials not only suppress weeds, cool the soil and help retain moisture, but they look good doing it. During the first week after application, they’ll also emit a pleasant aroma.
- hardwood – similar to evergreen chips, but with a different look; usually a rich dark brown. Be a little careful about using walnut chips. Many plants simply won’t grow when their roots come into contact with walnut.
Non-plant by-products – In general, most experienced horticulturists balk at the notion of using non-plant by-product mulch; they are somewhat of a last resort material.
- Stone and rock – most look great. The chief advantages are that it won’t blow away, and won’t degrade, which means that you won’t have to spend money to replace it year after year. However, you’re not helping the plant by using these products. In fact, using them around annuals and perennials usually adds additional heat stress. [Depending on the temperament of your kids, stone and rock can be quite fun to toss at cars, picture windows or each other. Of course if they’re the type of kid that would prefer to practice their violin in the solarium, then it’s less of a concern. ]
- Crumb rubber - a good use of a waste product. The best places for this stuff are around kids’ play equipment, paths, or areas that are too hot, too dry or too shady for plants to grow.
3. Should I choose an “aged” mulch product?
It depends on the situation. Aged mulch won’t rob the soil of nitrogen as much as new mulch. It’s better for newer plants that are just establishing their root systems. Aged mulch will only last about half as long as newly chipped mulch.
4. If I decide that an aged product is best, how can I be sure it’s aged?
You can usually tell by sniffing and feeling. Because it’s starting to decompose, aged mulch has a “pre-compost” smell and feel.
5. What about softwood vs. hardwood?
Hardwood (from trees such as oak, black locust, hickory, hackberry, etc) mulches tend to last a little longer than softwood (chips from silver maple, willow, honeylocust, etc.). Mostly, it’s a choice of color, texture and aesthetic appeal.
6. How deep should I apply the mulch?
Once again, it depends. For veggie gardens, an inch of dried grass clippings, straw, chopped corncobs or shredded newspaper works great. Annuals and perennials grow best with a couple inches of wood chips amongst them, and trees and shrubs would be well suited with 2-3. With any planting, make sure that the mulch is placed between the plants and not on top of the crown or pushed against the tree trunk.
7. I’ve seen mulch that has been dyed. It is ok to use?
Other than some of the hideous colors available - electric blue, pink, gold, etc - the dye used is relatively safe. No significant risk to pets or the environment.
8. How do the non-wood mulches really perform in the landscape?
They’re good for paths, and areas that don’t have plants nearby.]
9. When should I apply mulch?
Because the main purposes are to cool the soil, suppress weeds and hold in soil moisture, early summer is a good time to start applying mulch. In fact, applications made in early spring delay root expansion of newly installed perennials and annuals.
10. Should I be cautious of using mulch from a tree or lawn that was diseased?
No. Most plant pathogenic diseases are specific to the plant they infest. Mulch from a poplar tree infected with cytospora canker is very unlikely to cause a similar disease on dogwoods or coral bells. [Grass clippings from a lawn infected with rhizoctonia brown patch will not cause problems if scattered amongst bell peppers.]
11. What about pine needles or leaves from deciduous trees?
These materials make good mulch, but only if shredded first. In fact , the somewhat common “leaf mold” is simply shredded deciduous tree leaves. Both of these materials can be used for a season, then raked aside and placed on a compost pile.
All in all, using mulch is one of the best things you can do to help your garden thrive. Knowing when and how to use it as well as picking the best product for each situation is your challenge as a gardener.