Text by Adrian Higgins (c) 2019, The Washington Post
April is a good month to plant herbs - in pots, in raised beds, in designated herb gardens - and, like spring itself, these aromatic jewels speak to the promise of the growing season ahead.
Herbs have been used for millennia for their culinary (and other) powers. But for all their utility, herbs are great garden plants in their own right. Fragrant, textural, pretty in bloom and ever ready to provide aromatherapy with the brush of the hand, these plants thrive in hot, dry locations and can take care of themselves.
There is a price for this perfection. Many of the most popular herbs are from the Mediterranean basin and must endure less than optimum environments in hot, humid climates. With a bit of effort, the gardener can mitigate this climatic misalignment - but not fully overcome it.
What does this mean? Rosemary and lavender will never grow as large or for as long as in their optimum range, and if you seek to replicate, for example, a lavender hedge or a medieval-style knot garden, which rely on uniform plantings, you are setting yourself up for disappointment. Gaps will appear, and the uniformity will be lost.
Instead, view these herbs as semi-permanent perennials - integrated into a dry garden or grown in pots on the balcony or patio - and accept that they come and go.
Humid summers and frigid, wet winters are addressed by placing herbs in sunny, breezy locations and, most of all, in soil that is free-draining. The latter means amending clay soil; you could add horticultural gravel chips, chicken grit or sand, along with some compost. Avoid organic mulches, which will promote rotting crowns, especially in the winter. I mulch my herb beds with simple and cheap pea gravel, and as it gets worked into the soil from year to year, the effect is all to the good. The bed is then spruced up with a fresh topping of gravel.
Incorporating some ground limestone into the soil will make the plants happier - they like it on the sweeter side - and is particularly important for lavender plants.
Many herbs do well in containers, where you can control the growing medium and provide the drainage they need - no saucers under the pots, please. They will need watering more often than bed-planted herbs and should be fed a weaker a soluble fertilizer or at half-strength every couple of weeks or so. It is always best to water at the roots rather than the foliage.
Young transplants in small nursery pots should not be planted directly into large containers because the soil will stay too wet for the volume of roots and the plants may well rot. Place a new plant into a slightly larger container - going up two inches in diameter - and let it grow there for a few weeks before putting it in its permanent home.
Here's my advice for five herbs everyone should grow:
Lavender tends to look half dead in early spring, and it's not until new growth emerges in April that you get a sense of its survival. The temptation is to cut it back, but pruning stems below points of new growth will kill it.
The classic English lavender (Lavandula angustifolia) is the toughest of the clan, and stays compact and tidy, with foliage to about 18 inches and flower stalks another 12 inches or more. Hidcote and Munstead are the two most common varieties. At the National Herb Garden at the National Arboretum, curator Chrissy Moore points out a cultivar named Croxton's Wild, which has come through the winter in full leaf. In another bed, a variety named Tucker's Early Purple is similarly unscathed. Planted for five years and now mature, "it's doing swimmingly," she said. Graves is another dependable English type.
The big French intermediate lavenders or lavandins are pretty reliable under good cultivation, and older types such as Grosso have been superseded by superior ones. Gardeners in my orbit rave about a variety named Phenomenal, noted for its tolerance of heat and humidity. In Moore's beds, a variety named Sussex (sometimes sold as Super) is looking great now. Dutch lavender is a lavandin that is shy to bloom and is grown for its foliage, a beautiful silver gray, and its shape, a domed pillow.
Spanish lavender (L. stoechas) is more marginal in its hardiness but is beloved for the way its long-lived blooms are crowned with conspicuous tufts or bracts. Moore likes a compact, heat-tolerant variety named Silver Anouk, though it took a bashing this winter.
Tender lavenders such as fringed lavender (L. dentata) and fernleaf lavender (L. multifida) give a different foliage effect and if grown in pots can be overwintered in a cool, bright interior space (as can the hardier ones).
I used to go to a lot of trouble to get rosemary plants to live several years and thus got large plants. This was achieved by selecting a couple of hardier varieties - Hill Hardy and Arp - and growing them in optimum conditions. They didn't look as pretty or taste as good as others. Now I am apt to stick in the classic chef's favorite, Tuscan Blue, and we take our chances.
The prostrate rosemary is all right as a spiller in a container; I find it scruffy-looking in a garden bed, and it's the one variety you can count on to croak in the winter, being so flat on the ground.
There are an extraordinary number of thyme cultivars, some tiny in leaf size and texture and thus useful in the tightest of spaces or as part of a Lilliputian composition. They derive from a number of species and generally cleave into culinary and ornamental varieties, though I've used the latter in cooking. They are all highly aromatic and full of little blue flowers and visiting bees in late spring.
Golden lemon thyme and green lemon thyme are exquisite and have a citrusy quality to them, but they don't have the vigor or staying power of others.
I advise against copying the European practice of planting thyme between pavers, steppingstones and flagstones. It no more likes being stepped on than you do. Moreover, the stones get far too hot.
The biggest problem with thyme is the accumulated moisture in the crown of the plant. At the National Herb Garden, Moore tends two large embankments of thyme. The plants love the free-draining soil, and although there's an irrigation system, she turns it on only during dry spells (sprinklers and herbs are a dangerous combination).
Even when happy, clumps of thyme will have winter dieback. The solution is to cut back the dead growth and let healthy stems fill in the void.
Timothy Erdmann, horticulturist at Longwood Gardens in Kennett Square, Pennsylvania, says he cuts back thyme in late summer, creating new side growth before the winter sets in. "Plants respond better the following spring," he said.
Oregano takes several different forms in growth habit, hardiness and flavor. The tender sweet marjoram (Origanum majorana) is upright in the garden and prized by cooks but needs to be planted afresh each spring. Italian oregano (O. x majoricum) is hardy and also a clumper but not as sweet as majorana. The standard stalwart oregano is Greek oregano (O. vulgare subspecies hirtum), which creeps and spreads to the point of weediness. It is easily pulled and tamed.
The flavourful and aromatic Lebanese oregano, or Za'atar, is a tender, upright plant botanically O. syriacum. Grow it as an annual.
Basil is the resolutely annual herb in this group and should not be planted until nighttime temperatures are consistently in the 50s or above. It will decline in early autumn with cooler nights, at which time it can be harvested to make pesto for freezing.
The popularity of basil in Mediterranean and Asian dishes has led to a surfeit of varieties, ranging from giant-leafed Genovese types to compact, miniature-leafed versions. Thai basil tends to be more open in its growth habit, and spicier. Italian basil is beloved for its anise note and sweetness.
Basil has always been prone to powdery mildew, especially toward the end of a dry but humid summer. This gives leaves an off-putting white coating. Another disease named downy mildew has arrived in recent years and is more devastating.
Both ailments are eased by growing basil in uncrowded areas of free air circulation, but the downy mildew will finish your plants. The disease progresses through a plant: Yellowing leaves turn brown and the leaf undersides become a fuzzy gray-purple. Thai basils tend to be freer of the disease.
When you buy plants, inspect them for signs of disease. Several breeding programs are underway to produce resistant varieties; the difficulty is in trying to add disease-resistant bloodlines without compromising flavor. One on the market this year is basil Amazel, introduced by Proven Winners and developed at the University of Florida. "It should be reasonably easy to find, but it's still a first-year plant, which always has some challenges," said Kerry Meyer, Proven Winners program director.
Basil goes through a leafy stage in the first half of summer and then has an urgency to flower. Once the flower stalks appear, flavor begins to turn bitter, so the gardener should cut back stems for harvesting as a matter of course. This delays blooming but doesn't prevent it. The best course is to start young plants again through the season. Basil grows easily from seed. Sow successively over the summer in pots and thin and transplant seedlings as they grow - or keep them in their containers. Basil likes more moisture than other herbs and is better planted separately in richer soil. Erdmann recommends keeping your basil plants separate as well to minimize disease problems.
Vegetable seeds need at least two thinnings to allow plants the room they need to develop properly. Wait until seedlings are a couple of inches tall before their first winnowing. If they are frail and congested, use scissors to remove some without disturbing the keepers.
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