Right after I finished mulching my rose garden with free wood chips I got from a tree service, I read that wood chips suck all the nitrogen out of the soil. Should I fertilize now?
As soon as you spread mulch, there’s a population boom of bacteria, fungi, and other soil microbes that work to decompose organic matter. These beneficial organisms consume some of the nitrogen present in the soil. The nitrogen loss is temporary, however, because the nitrogen is once again available to plants when the microbes die.
But in the meantime, the thin layer of soil that is in direct contact with the mulch will relinquish some of its fertility. The depletion of nutrients does not extend deep into the soil, so it won’t likely affect anything other than the shallowest-rooted annuals.
The benefits of organic mulch outweigh the possibility of a temporary nitrogen shortage. Mulch conserves moisture and contributes to a healthy root zone. It also helps to suppress weeds. As mulch decomposes, the nutrients held within it—including a small amount of nitrogen—are released.
For roses and other plants with high nutrient needs, it’s a good idea to keep an eye out for nitrogen deficiency, whether you’ve mulched with wood chips or not. Plants lacking nitrogen grow slowly and exhibit pale or yellow-green leaves; in extreme cases, growth may be stunted.
To preclude the chance of nitrogen deficiency, many gardeners make a habit of distributing a small dose of slow-release nitrogen fertilizer every spring to roses, perennials, edible crops, and other heavy feeders. Good organic sources include alfalfa meal (about 5 percent nitrogen by weight), fish meal or fish emulsion (5 percent), blood meal (12 percent), and feather meal (15 percent). Compost and worm castings also contain small amounts of nitrogen. —Doug Hall
Can I use my Christmas tree for mulch?
The boughs of fir, pine, spruce, and other evergreen trees are a good insulator for dormant perennials. Unlike some winter mulches, like unshredded leaves, they don’t pack down into a solid, oxygen-excluding layer. And when spring comes, they’re easy to rake aside.
Discarded Christmas trees appear curbside at an ideal time for adding winter mulch in my Zone 6 garden. By late December, the ground has chilled (if not frozen an inch or two deep) and plants are dormant. Hopefully, any field mice in the neighborhood have settled down elsewhere for the winter and won’t find habitat in my mulch. I scavenge the neighborhood before trash day, bringing home five or six trees to cut apart.
It’s quick and easy: Just snip the tree’s branches off with loppers. Place the boughs over the crowns of perennials or around roses.
The purpose of winter mulch is not to keep plants warm but to keep them consistently cold and dormant. Unmulched plants are exposed to temperature fluctuations, alternating between overnight freezing and daytime thawing when the sun hits the soil. Some plants shrug off these repeated temperature changes, but anything of marginal hardiness will appreciate the extra protection it gets from a layer of evergreen boughs. —Doug Hall
As a new gardener, I’m not sure what I need to do to get my strawberry bed ready for winter. Do strawberries need protection?
A layer of loose mulch over the crowns of strawberry plants in winter shelters them from temperature fluctuations and keeps them dormant until spring arrives. Mulch also conserves soil moisture for these shallow-rooted plants. The only regions where winter mulch might not be needed are places with dependable, winter-long snow cover and, at the other extreme, places where the temperature never falls below 20°F.
Straw is the obvious choice for mulching a strawberry bed, but other lightweight mulches like pine needles and evergreen boughs also work. Don’t use mulches that become soggy and heavy—leaves, for example.
Allow your strawberries to go dormant before applying mulch. Applied too early in fall, the mulch can delay dormancy and become a haven for rodents. Wait until a hard freeze—between 20°F and 25°F—has flattened the leaves, then scatter 2 to 5 inches of mulch over the entire strawberry bed.
As growth resumes in early spring, rake the mulch into the pathways between beds—but keep it handy in case it’s needed to protect from late frosts. —Doug Hall
I’m worried about using mulch near my house for fear of attracting termites. What is the best alternative to leaving a strip of bare soil next to the foundation?
The bad news is that termites are ever-present in all but the coldest climates. The good news: You don’t have to invite them into your home.
The strip of bare soil you’re trying to avoid is actually your best defense against these destructive, wood-eating insects. A study at the University of Maryland showed that termites colonize the moist soil beneath mulches of all types, including non-wood mulches like pea gravel and plastic film. Entomologists report that soil moisture, more than the presence of wood, determines where termites establish their colonies. Because their soft bodies are susceptible to desiccation, termites avoid dry soil.
Your strategy, then, is to keep a “dry zone” a foot or two wide around the house. Contour the ground so it slopes away from the foundation. Install roof gutters and direct the downspouts out into the yard. Keep plants—especially plants that offer a dense cover of foliage—at least a foot from the house. Design landscape beds nearest the house so they can be sustained without supplemental irrigation, and use no more than an inch of mulch in these beds.
Keep a watchful eye out for signs of termite infestation: pencil-thin mud tubes on foundations and walls, the occasional “swarming” of winged adults, and, of course, damaged wood. —Doug Hall
Water is the lifeblood of gardens. When summer heats up and natural rainfall becomes scarce, gardens can falter—unless the gardener steps in with a watering can. Water is a precious—and in some communities, expensive—resource that is not to be squandered. Here are some ideas to keep your summer garden thriving without wasting water:
• Soil preparation. Soil that is rich in organic matter, porous, and fertile encourages healthy, deep root systems. And far-reaching root systems are better able to provide plants with the moisture they need in times of drought. Midsummer isn’t the best season for amending the soil; save this task for fall. In the meantime …
• Mulch. Mulched soil loses less moisture to evaporation. It also stays cooler, which keeps roots and beneficial soil microbes happier. Straw, leaf mold, or dried grass clippings are good mulches for vegetable beds. Shredded wood, pine straw, or bark are good under shrubs and in flowerbeds. Bonus: Mulch prevents many weeds from germinating.
• Drip irrigation. When you water, use a technique that applies the water exactly where it’s needed. Soaker hoses and drip tubing deliver the water directly to the soil (as opposed to a sprinkler that flings water into the air and allows much of it to evaporate). Hand watering, with a hose or watering can, also ensures that the water lands where it is of greatest benefit to your plants. —Doug Hall