Growing Herbs in the Air

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For many home gardeners, a hanging pot of herbs is just that: a potted herb plant that’s hung up with a wire or macrame hanger. Ideally, the herb stems extend and hang down over the sides of the pot, eventually engulfing it in a cascade of lush, fragrant foliage. But it doesn’t usually work out that way; more often, the result is thin, leggy stems producing widely spaced foliage that doesn’t really cover the pot at all.

At the U.S. Botanic Garden in Washington, D.C., we’ve become well known for the lush hanging plants that bask in the summer sun and greet our visitors outside the conservatory entrance. Four years ago, we began replacing some of the standard ivy geraniums, petunias, and lantanas with creeping, cascading ornamental herbs—catmint, peppermint, thyme, oregano, and rosemary—and the results have been outstanding. What you see in the photos is one season’s growth: a giant ball of foliage suspended in the air!

A lush herb basket like this can become a brilliant focal point almost anywhere it can be hung—a post or fence, a tree, an overhang, or a wide doorway. Because of the exposure near the conservatory, we chose sun-loving herbs for most of our baskets, and we made them and the supporting structures quite large because the space is large. We installed a tall “tree” made of metal pipe, and from it we hung eight mammoth herb baskets. The baskets themselves were 24 inches in diameter, made of wire, and suspended by chains from the protruding arms of the “tree”. The ball of herbs in each basket grew up to 4 feet wide. This is probably too large for most homes, but the method of preparing the baskets (described below) also works well for smaller sizes.

The methods we use for making these hanging baskets of herbs aren’t really new; the principle is similar to that of a strawberry jar. After you understand the basic idea, you’ll probably want to make hanging baskets with many of your favorite herbs.

The plants listed below, and many others, need to rest in winter; they become weak if kept in full growth all year. Herb baskets should be brought indoors when days become short. Keep the plants cool and underwatered, and do not fertilize during this period.

There are three major considerations in deciding where to hang your herb baskets. The first and most obvious is that they must hang from a sturdy support because the baskets are quite heavy just after watering. The second is that the soil in the basket is enclosed only in a wire frame lined with a thin layer of unmilled sphagnum peat. After watering, the basket will continue to drip for as long as an hour, which rules out most indoor locations. On the other hand, roots consistently have good aeration—in fact, it is just about impossible to overwater them—and the baskets can be planted on all sides to create a ball of foliage and flowers. The baskets remain full and beautiful throughout the summer, but with such excellent drainage in the hot, humid Washington weather, they need to be watered daily.

The third consideration is the sun or shade requirements of the herbs in the basket. A reasonable approach might be to select plants after choosing a location for hanging the basket.Any plant that grows vigorously in your garden is a good candidate for use in a hanging basket, although woody herbs are less likely to give good results, and the tiny-leaved Corsican mint, though interesting, is easy to overwater, even in a hanging basket. If your chosen site is shady for much of the day, try planting peppermint varieties, pennyroyal, and other Mentha species.

Herbs can be mixed in a hanging basket as long as their sunlight and water requirements are similar. All the herbs in the list below, except perhaps peppermint, can be planted together in any combination. Thyme and catmint make a good pair in full sun; peppermint and parsley get along nicely in partial shade with a little more water. Most mint varieties are attractive combined with shade-loving annual flowers, such as Johnny-jump-ups (Viola tricolor), that grow well under the same conditions in which the mints thrive. After the flowers die back, the mints will grow over them and fill in the basket.

Preparing the Basket

We begin preparing our herb baskets in late winter in the greenhouse and hang them outside from May through September. We’re always careful to keep them out of direct sunlight and strong wind for the first week or so after we bring them out; the sun burns the leaves and the wind desiccates them if the plants aren’t given a chance to harden off after the lush life of the greenhouse.

Herbs thrive on pruning. Don’t hesitate to pinch and clip the plants back as needed to keep them full.

If you don’t have a greenhouse, purchase well-established plants of a size appropriate for planting out in the garden. These will still require a week or so of hardening off before they can tolerate full sun and wind.

Wire baskets like the one shown are available in a wide variety of sizes; select one that is about one-third to one-half the desired final diameter of the foliage ball. (If you’re planting an herb that will hug the basket closely, such as Corsican mint, the basket should be closer to the desired size.) These wire baskets are light in weight for their size, but more important, the spaces on the sides are large enough for plants to grow through. The sphagnum basket lining nearly covers the wire frame, and its appearance blends well into most garden settings.

The number of plants you’ll need can be estimated from the size of the basket and the anticipated spacing of the plants, typically one every 3 to 4 inches around the side of the basket and in the top. Add 30 percent more plants if you’re going to plant two rows around the side.

Give yourself plenty of space for working on a potting bench or countertop.

• If hangers are connected to the basket, remove them.
• Soak unmilled sphagnum moss in warm water until thoroughly moistened; overnight is best. Squeeze out each handful as you apply it.
• Line the inside bottom of the basket with the moss to form a layer about 11/2 inches thick.
• Line the inner sides of the basket in the same way, and press the moss against the wire and partway through the frame until the filament partly covers the wire.
• After lining the inside of the basket, line the top edge of the wire frame as well.
• Check your work, filling in any thin spots so that the layer is of uniform 11/2-inch thickness.
• Fill the basket half full with soil mix and tamp it down just enough to remove air pockets. My favorite soil mix comprises 70 percent Pro-Mix BX, 15 percent loam, and 15 percent compost, but many other combinations work well.

Planting

• Remove a plant from its pot, gently loosen the roots, and wrap the entire plant in a paper towel to protect the foliage.
• With your finger, poke a hole outward through the sphagnum at the soil level and gently push the plant, top first, through the hole. While holding onto the roots, gently tug on the paper towel from the outside. When the top is through the wire, remove the paper towel.
• Repeat this procedure every 3 to 4 inches around the side of the basket.
• Add enough soil to cover the roots well, then tamp down lightly. If the basket is large, you may want to add another row of plants just above this level. Plant it in the same way as the first row, but stagger the new plants between the plants of the first row. Cover the roots of the second row with soil and tamp down lightly.
• Plant the top of the basket as you would an ordinary pot, with the plants growing upright, 3 or 4 inches apart.
• Sprinkle on a slow-release fertilizer, such as Osmocote, according to the manufacturer’s instructions.
• Water gently and thoroughly; a wand-type sprinkler is useful for this. Hang the basket in your chosen location and fasten it securely.

Care of the Hanging Basket

Water daily during hot weather, preferably in the morning so that excess water can evaporate—this will lessen the likelihood of disease. When it is breezy and the humidity is low, you may need to water twice a day. Test the top layer of soil; if it feels dry, the basket needs water. Tepid water is best, but it’s difficult to keep in constant supply; cold will do. Always apply it until it runs out the bottom of the basket. Soilless peat-based potting mixes that are allowed to become dry can develop areas within the soil that resist moisture, even when you think you’ve soaked the soil completely. Rewatering after several minutes can sometimes prevent this problem; another way is to use a potting mix in which the peat is thoroughly shredded and not in clumps. We prefer Pro-Mix BX or Metro-Mix for this characteristic. Be sure to moisten the potting mix before planting.

In addition to the slow-release fertilizer, use a soluble fertilizer in the water every two to three weeks during the growing season.

Herbs thrive on pruning. Don’t hesitate to pinch and clip the plants back as needed to keep them full. Remove old flowers. A great way to invigorate many herbs is to shear them back after they bloom. All the herbs listed below will benefit from this treatment; catmint will rebloom later in the season if cut back after flowers have faded. If pruning of any herb is severe, the plant may take a long time to recover. It may be better to cut it back in stages.

Sources

Well-Sweep Herb Farm, 317 Mt. Bethel Rd., Port Murray, NJ 07865. Catalog $2.
Goodwin Creek Gardens, PO Box 83, Williams, OR 97544. Catalog $1 refundable.


Holly Shimizu is Assistant Executive Director of the U.S. Botanic Garden in Washington, D.C., and a lover of herbs and old roses.