Before you haul yards of expensive mulch into your yard this spring, make sure you know how to correctly mulch your trees and shrubs.
When done correctly, mulching suppresses weeds, helps retain moisture, inhibits plant diseases, moderates soil temperature, builds organic matter, and provides a buffer so lawnmowers won’t accidentally nick trees.
But when mulching is done incorrectly it can actually damage trees through insect infestation, fungus growth, and more.
Here are useful tips to help you get the most of your mulch investment this spring:
Mulching ‚”do’s”
- Spread it Out.A good mulch bed should extend out at least three feet from a tree’s trunk in all directions, though wider is better.
- Make it Natural. The best mulches are fairly coarse and woody, like wood chips or ground bark. Leaves, pine needles, compost, straw, and grass clippings also work fine. The coarser the mulch, the better.
- Keep it Under 4 Inches. Mulch bed depth should be maintained at 2 to 4 inches.
- Include Several Trees and Shrubs. Manage plant groupings by creating mulch beds that surround several trees and shrubs to separate and easily manage tree and turf areas. Be creative- you don’t have to stick with a perfectly round contours.
- Mulch Around Established Trees. Just spread a layer of mulch over the existing grass — it will smother the grass. As the tree grows older, the mulched area should expand with the tree. On older trees, a mulched area with a diameter of 12 feet is effective and attractive.
- Use the Right Mulch. For poor soils, use well-composted mulch to build up the nutrients. Soils that are healthy will do fine with a highly stable softwood bark (such as cypress bark), which doesn’t break down as easily.
Mulching Don’ts
- No Volcanoes, Please. The biggest no-no when mulching is to create a ‚”mulch volcano” that is six to eight inches high around the base of the tree. This results in the decay of the bark and will girdle the tree by killing the vascular tissue under the bark, foster infection, create a breeding ground for bad pathogens, and can create habitats for rodents that chew the bark. Volcano mulching also traps moisture around the tree trunk and root flare, leading to decay and, eventually, structural failure.
- Avoid Fine Mulch. Thick blankets of fine mulch can become matted and prevent the penetration of water and air.
- No Orange Mulch. Don’t use artificially colored or exotic wood mulches, which can leach chemicals into the soil. Mulch made from Redwood or Cedar trees can significantly change soil pH.
- Don’t Let Mulch Sour. Low oxygen levels (from packed-down mulch) creates a toxic ‚”sour” mulch – which may give off pungent odors, and even worse, the compounds produced (methanol and acetic acid) can kill young plants.
- Don’t Keep Adding New Mulch on Top of the Old. While mulch does decompose, you do not want to accumulate excessive mulch year after year by adding fresh mulch every spring. If you want the look of fresh mulch, break up the old with a rake, and only add a layer of new on top if there is less than 4 inches in depth.