Maintaining a healthy, vibrant garden of any kind means paying attention to the water and nutrient needs of your plants; managing competing weeds; and preventing or stopping disease and insect problems before they get out of hand. Fortunately, herbs are among the easiest plants to grow — typically, they need much less maintenance than other garden plants. By following these basic tips and techniques, your herb garden will practically care for itself.
In most areas, rainfall provides adequate moisture for herbs. Covering the surface of your garden beds with a 1- to 3-inch layer of organic mulch (such as shredded bark, leaves, or compost) will help retain soil moisture, suppress weeds, and prevent soil erosion. Water is essential to plant growth. When rainfall isn’t enough, deep watering once or twice a week can help.
If an extended drought causes some plants to wilt, deep watering (permeating 1 to 3 inches below the surface) can help them recover. Deep watering ensures healthier root development than shallow daily watering, which simply encourages the growth of roots upward toward the bit of moisture that is being provided. Before watering, loosen the soil that surrounds the plants to encourage easier absorption and discourage runoff. Water in the morning, if possible, so that any droplets that splash onto foliage can evaporate during the day. Using a soaker hose or drip irrigation will also keep foliage dry, protecting your plants from diseases (such as fungal infection) promoted by dampness. By releasing water close to the root zones of plants, drip systems also foster deep root growth and minimize runoff and evaporation.
Soaker hoses deliver water efficiently to plant roots; less moisture is lost to evaporation.
A Healthy Diet
For most herbs, a yearly application of compost is enough to keep their soil in good condition. But some herbs — especially fast-growing annuals such as basil, cilantro, and dill — benefit from an occasional boost of organic fertilizer, such as fish emulsion or liquid seaweed. Avoid feeding plants too much nitrogen (such as in manure) because it can encourage weak growth that’s more susceptible to disease and the ravages of cold weather.
Once or twice a month, from spring to midsummer, treat your herbs to some compost “tea” — an effective liquid fertilizer and preventive for some mildew diseases. To make compost tea, place 1 quart of finished compost in a 5-gallon bucket, and then fill the bucket halfway with water. Steep the mixture for 5 to 15 days, then strain out the compost. Reserve the liquid and dilute it until it is the color of a cup of black tea. Spray the liquid on plant leaves early in the morning, or apply it to the soil around fast-growing herbs.
Routine garden maintenance — weeding, pruning, and watering — keeps an herb garden healthy and beautiful.
The Magic of Mulch
Mulch — a thin layer of organic or inorganic matter laid on the soil’s surface — helps keep soil cool during the growing season and provides insulation during the dormant months. Mulch also slowly releases nutrients into the soil, retains moisture, and suppresses the growth of weeds around plantings.
The best organic mulches for garden plantings are shredded leaves, pine needles, and compost. Compost provides the added benefit of protecting plants against diseases. Studies at Ohio State University showed that a 2-inch layer of compost mulch blocked weeds while greatly enhancing plant growth. High-carbon materials, such as wood chips and sawdust, can inhibit plant growth in the garden, but they’re perfect for mulching pathways. A double-layered mulch of damp newspapers topped with chipped bark or gravel works even better for stopping pathway weeds.
Apply a 2- to 4-inch layer of mulch over garden beds, but keep it several inches away from plant stems and trunks so that it doesn’t damage the bark and encourage insects and disease. Replenish organic mulches every few years.
If mulch isn’t enough to stop the growth of aggressive, unwanted plants, use a trowel or shovel to carefully remove these plant by their roots. Continue to inspect the area because new plants can sprout from root fragments or seeds.
Proper pruning encourages plants to produce healthier, bushier growth. Follow these guidelines to keep your herbs growing strong for years to come:
• In midspring to late spring, prune woody, aromatic herbs such as lavender, sage, southern-wood, and rosemary. Use clean, sharp gardening shears to remove older, leggy growth. This will prompt the plant to generate young, healthy stems.
• In early summer, prune flowering stems to promote extended foliage production of such herbs as basil, Roman chamomile, chervil, costmary, lemon verbena, oregano, and tarragon. The flowering stems of these herbs will divert the plants’ energy from the formation of fragrant or flavorful foliage. To prevent or delay flowering, use gardening shears to cut the flower stems at their bases. For tender herbs such as basil, pinch off flowers as they form to prolong the production of aromatic foliage.
• In the middle of the growing season, after they have flowered, cut back catnip, comfrey, lemon balm, marjoram, mint, sweet cicely, and salad burnet. These herbs produce less-flavorful and tougher foliage later in the season. Cut the plants back by one-third to one-half to encourage a burst of tender new foliage.
Planting in a protected area, such as next to a fence or building, can help herbs at the limit of their cold-tolerance survive winter. Mulch, row covers, and cold frames also offer protection against cold.
Extending the Growing Season
For annuals and tender-leaved perennials in temperate regions, the first and last frosts of the year generally signal the beginning and the end of the growing season. Neither annuals nor tender perennials tolerate temperatures below freezing: A night of frost can turn a healthy plant into a cluster of blackened, shriveled sticks. On the other end of the spectrum, plants accustomed to cool weather can fail to germinate under a blistering sun.
Sheltering structures can help moderate soil and air temperatures below and around plants, protecting individual plants or whole beds. In hot areas, a shade net of woven polypropylene fabric stretched over wire hoops or a movable wooden frame can keep soil cool and moist. Shade netting can be placed over newly sown seedbeds and transplanted seedlings to shield them from drying winds and to buffer the intense heat and light of the sun.
In cool weather regions, a cold frame can be used to trap the sun’s heat and begin the growing season a few weeks earlier in spring and extend it a few weeks later in fall. A cold frame is a low, bottomless, boxlike structure that acts like a greenhouse. It usually has a higher south-facing back wall, a white interior to reflect light throughout the box, a glass or clear plastic cover that allows the sun’s rays to penetrate, and a thermometer to monitor the interior temperature. You open the cover to reduce the temperature when it climbs too high for the plants inside. Cold frames are good for starting seedlings in spring, for hardening off seedlings that have been started indoors, and for extending the harvest season of cold-sensitive plants. A cloche or a bell-shaped cover (made from such materials as a plastic milk jug) can also be used to protect individual plants from cold temperatures in spring and fall.
In all climates, strong winds can prevent herbs from developing sturdy root systems, thereby preventing healthy growth. A wooden fence or row of planted shrubs can act as an effective windbreak, providing enough shelter to allow some marginal plants to survive otherwise.