Good grooming can enhance and prolong the beauty and productivity of herbs. Even in an informal garden, ungroomed plants look weedy and slovenly, not charmingly carefree: there’s a difference between a natural look and a natural disaster.
The four horsemen of the garden apocalypse are melting out, invasiveness, legginess, and seediness. These evil traits can make an unhappy mess of your herb garden.
Many herbs, especially lamb’s-ears, thyme, and catnip, melt out (contract a fungal disease) under prolonged heat and humidity. Foliage and flowers turn brown or black and may die away from the center, leaving an unsightly bare patch.
Picture a 6-foot-4-inch adolescent who weighs 145 pounds–that’s legginess. Leggy herbs look skinny and have elongated stems that flop over readily. The plants may receive inadequate light due to excessive shade or overcrowding. The competition for light and soil nutrients often results in inferior flowers and oil production.
People described as having gone to seed have let themselves become unattractive or sloppy. The reference is to the scruffy appearance of many plants (especially annuals and biennials) after they have set seed. Having created offspring, these plants no longer need to impress potential pollinators or direct their energy into ripening seed.
To prevent seed formation in herbs grown for their foliage, pinch out (remove) flower buds. To prevent an overabundance of volunteer seedlings of such herbs as mallows, sweet Annie, and garlic chives, you can enjoy the flowers but cut them off before the seeds mature. Do encourage “seediness” in herbs grown for seed, such as coriander, dill, anise, and fenugreek.
Alan Greenspan’s description of the stock market as having a case of “irrational exuberance” could also describe the way herbs such as mint, lemon balm, borage, and tansy grow–swallowing their neighbors with their robust growth. When invasive plants migrate out of bounds, it’s not enough just to cut back foliage: you need to dig them up, roots and all. Some gardeners are able to limit their growth by planting invasive herbs in containers or in isolated beds.
Battling the horsemen
Fortunately, the horsemen of the garden apocalypse are more bothersome than lethal because they have one glaring weakness: no element of surprise. An experienced gardener can see them coming and take defensive measures: pinching or cutting back, dividing, and staking.
Pinching or snipping off an inch or two from the tip of a stem removes the stem’s active growing point. The result is to encourage the growth of lateral shoots, creating a bushier plant–important when an herb is grown for its foliage or is prone to flop.
Use your fingers, scissors, or hand pruners to nip off the stem tip as far as the first node (the point at which one or more leaves grows out of the stem). Pinching back should be done early in the growing season and may be repeated as needed.
Cutting back is a more severe form of pinching back that significantly reduces the size of a plant to promote the growth of new foliage, reduce sprawling, and stimulate a second flush of blooms. Cutting back also increases air circulation and light around plants, which may decrease their susceptibility to melting out.
Many gardeners fear cutting back plants–they’re so eager to get things to grow that it seems absurd to chop a plant in half. Fortunately, most gardeners get over their hesitations pretty quickly when they learn how cutting back improves vigor, shape, and flowering, as well as giving them a supply of herb clippings to dry or use right away.
Most nonwoody perennial herbs can be cut back close to the ground either in late fall or when new growth appears in early spring. Some gardeners in colder areas prefer to leave old stems in place over the winter to trap snow, which insulates the crowns from temperature extremes.
Use sharp hand pruners to cut stems, grabbing a clump of stems and cutting below them. For safety, wear heavy gloves and keep your eye on the blades.
Dividing plants takes time and muscle, but it’s the most important maintenance task for the long-term health and appearance of many perennial herbs. Whether to divide a plant depends on how robustly it’s increasing in breadth, whether it’s outgrowing its allotted space, and whether it’s dying out in the middle. A perennial plant can overcrowd itself when its offspring grow too close together. The resulting competition for soil nutrients and light can foster weak, leggy growth and reduce air circulation around the plants, which may predispose them to fungal disease. Overcrowded plants can be given a new lease on life by digging them up, discarding dead, diseased, and woody parts, and replanting a few healthy parts in amended soil.
Dividing is commonly done in the spring, although irises and daylilies are usually divided in summer after they have finished blooming. With a shovel, dig up the entire plant. If it’s not too overgrown, you may be able to pull the clump into two or more smaller clumps. More often than not, though, you’ll need to use a stout knife, spade, ax, or two pitchforks held back to back to separate the plant into manageable chunks. Work some organic matter into the soil and then reset a few healthy sections following the spacing recommended in the guidelines at right.
A little staking goes a long way to restore order to a chaotic garden. It’s even better, and loads easier, to install the stakes early in the season even if the plants don’t need it at the time. They’ll be much less conspicuous because the plant will have grown up around them.
Choose sturdy wooden stakes for tall-growing herbs such as mullein or foxgloves, tying the stems loosely with twine, raffia, or a strip of nylon stocking. Round metal hoops on legs work well for shrubbier,multistemmed plants such as dill and fennel, but Y-shaped branches pushed into the ground around the plant give a more natural effect.
Maureen Heffernan of Cleveland Heights, Ohio, is the director of education and public programs at Cleveland Botanical Garden.