A newly mulched bed with freshly cut bed edges makes a landscape look neat and well tended.
Mulch is more than "just the icing on the cake" to make your garden look well-cared-for during the summer months. More important are its major functions in reducing weed growth, moderating soil temperature, and slowing the evaporation of water.
Mulching might seem like a simple enough job, but there are a few points to remember:
Mulch can kill trees if it’s packed up onto the trunk like a volcano.
© George Weigel
How much mulch?
While some mulch is a good thing, more isn’t necessarily better. Too deep a layer prevents essential oxygen from reaching the soil, causing root suffocation. Always keep mulch at least a few inches back away from the crown of all plants. A layer three to four inches deep is plenty around trees and shrubs, but moisture and wood-decaying organisms in most mulches can rot bark when packed against trunks and stems. For trees and shrubs, it should not be deeper than where the base of the trunk begins to flare into the root system. Mulch can kill whole trees if it’s packed in excess quantities against a tree’s trunk – a practice known as “volcano mulching”. This is seen way too often particularly in street plantings and public places that have been treated carelessly. For perennials (2” deep), and annuals and veggies (1” deep), it is critical not to apply mulch too close to the crown of the plant to allow for air movement. If you already have enough mulch in place, no need to add more; if the plants are suffocated remove some of it. Fresh mulch can go on top of old mulch, but loosen the existing layer first if it’s matted down or crusted to improve drainage and air movement.
Drainage and oxygen exchange is helped if you break up matted old mulch before topping it with new mulch.
© George Weigel
What to use for mulch
Weeds are tough to beat and invariably weed seeds find their way back into the garden, carried in by wind and birds. The average mulch not only can’t stop these, it often serves as a handy growth medium. However, Preen Mulch Plus has an added weed preventer in it so it blocks weeds from germinating for six months. It is available bagged at Lowe’s and independent garden centers. This product comes in three non-fade colors: midnight black, russet red and chestnut brown. Each bag covers up to 12 square feet since it only needs to be applied to a depth of 2-inches to suppress weed growth, instead of the usual 3-inch depth recommended for other mulches.
Leave a lip of two or three inches while cutting bed edges so the lip catches mulch and prevents it from migrating onto the surrounding lawn or sidewalk.
© George Weigel
Before mulching, use an edging tool to cut a sharp edge around garden beds. This prevents lawn grass from creeping into garden beds while making a neat edge that looks nicely tended. Cut a “lip” of two or three inches around the edge so that it catches mulch that might roll down the bed and fall into the adjoining lawn or sidewalk.
After you’re done applying and smoothing the mulch, soak the beds to settle it.
Mulch can be applied either before or after soil preparation of new beds. Some pros prefer to mulch the entire bed free of plants ahead of time, and then make holes for the plantings, being sure to pull away excess mulch from the crowns. Others prefer to plant first and then mulch around them.