Many new gardeners assume that mulch is a magic bullet to conquer weeds and grass in landscape beds. I’ve watched landscape crews dump a thick layer of mulch on healthy, vigorous weeds, and shake my head, knowing that they have just set up a client for bitter, delayed disappointment. Mulch MIGHT smother a few small, puny weeds and grasses, but not Bermudagrass, the turfweed of choice for many homeowners in the South. And mulch won’t smother most weeds, especially if they’re already up and growing for the season.
So why bother to mulch? Is it mulch ado about nothing?
Far from it. When mulching is done properly, it does many good things for your garden beds:
- It covers the weeds and showcases your plants. Your garden’s admirers won’t have to wonder if they are oohing and ahhing over a real plant or a weed. (That assumes you continue to weed after the mulch is applied, of course.)
- It helps your soil maintain moisture and coolness. Which is a good thing when summer heat hits, AND a good reason to not put it down until the soil warms up and dries out a bit in the spring. Case in point: Clematis plants are botanically bipolar: they love sunny conditions for their leaves and blooms, but need cool shade for their roots. Some light/heat reflecting light-colored stone and/or a layer of mulch can help create the perfect condition for your clematis to do its very best.
- If you first pull and/or spray the weeds, then apply mulch, it will help retard the growth and spread of weeds. It reduces your weed-pulling time, but it won’t make your landscape maintenance-free.
So what kind of mulch is best? We use both hardwood and pine needles in our beds. They both have their pros and cons:
- Both break down over time and add to the soil’s organic content.
- Ergo, both will need to be reapplied frequently – typically once or twice a year around here.
- Both can become a fire hazard. Pine needle mulch is strongly discouraged in the dry western states, but in the southeast we get enough moisture and humidity to negate that problem. Conversely, hardwood mulch can become a fire hazard when heat and humidity create conditions that lead to spontaneous combustion.
- Any mulch can float away in heavy rain, so be sure your downspouts have a clear path to direct excess rainfall outside your landscape beds.
- Pine needles are slippery so don’t use them on paths.
- Hardwood mulch can invite termites, so care should be taken if using them around foundations.
- Pine straw is lighter and easier for a one-person mulch “crew” to put down.
- Hardwood tends to look a little neater and more compact.
Whichever one you choose should be based on your personal tastes and situation. Contrary to popular myth, pine needles will not create highly acidic soil conditions. They can gradually affect a soil’s pH levels, but it takes a lot of years and a lot of pine needles to make a notable change in your soil’s pH. You can use pine needles around acid-loving plants like Hydrangeas and blueberries, but don’t assume they are a substitute for regular applications of fertilizer and magnesium to keep your pH in the optimal range.
And finally, know that some plants don’t fare well with mulch, such as irises. Mulch tends to keep the soil too moist, leading to rotten tubers and providing an inviting place for root pests to breed. Ditto for grafted roses – you can pile up mulch in the winter to protect the graft union, but pull it away during the growing season. Peonies will tolerate some mulch, but a heavy mulching can lead to reduced blooms the following year while the plants adjust their root systems to the appropriate depth. In the veggie garden, mulch around tomatoes can prevent soil-borne diseases from splashing on the plant leaves, but their fiery cousins, the peppers, tend to do better with bare soil or a thin piece of slate to soak up more thermal energy and keep the roots on the warm and dry side.