Nearly every gardener eventually runs out of space. It’s a universal condition. Gardens are seldom large enough to accommodate every plant we want to grow. As a result, we tend to overcrowd our plantings to make them all fit. For the apartment dweller or urban gardener, the problem is even more pronounced. To have a garden on a small concrete patio or tiny balcony is not impossible; it just requires more imagination. One solution is to go up instead of out. If you think in terms of three dimensions rather than two, the sky’s the limit.
There are a number of ways to add this element of verticality to your gardening, as well as products on the marketplace to help you do it. The most remarkable example I’ve seen was in an herb garden I visited many years ago at a small British herb nursery near the border between England and Wales. I remember it clearly because it was so simple, and it illustrated the ingeniousness of vertical gardening beautifully. It was an entire herb garden of about sixty plants in a space no larger than the size of my desktop.
Stack ’em up
The owner of the nursery had stacked three whiskey barrels of different sizes and planted the exposed soil with herbs. The resulting raised beds demonstrated all the virtues of a good herb garden: beautiful foliage and textural contrasts; lush carpets of flowers; intriguing habits of growth; alluring fragrances; and plants with a variety of medicinal, culinary, and aromatic uses.
The plants in the lowest tier were at knee level, and those in the topmost barrel were at eye level. In addition to providing a splendid visual treat, this arrangement put every herb within reach–to touch, smell, and harvest with no need even to bend down. I suspect that the garden was watered from the top, allowing the water to drain down to each of the plantings below.
What I enjoyed most about this garden was the variety of plants that it held. Many common herbs were in this barrel stack, including some that you might think were too large for container growing: lovage, fennel, upright rosemary, and culinary sages. Selective removal of flower or seed stalks, the restricted root zone, and natural competition among the plants, however, restrained the growth of the larger herbs and kept it manageable. The owner avoided growing herbs such as mint, horseradish, and the spreading artemisias, whose aggressive root systems would have taken over the planting in no time.
Herbs cascaded over the edges of all three barrels, showing off the foliage and blooms of upright thymes, prostrate rosemaries, winter savories, and gray santolinas. Although the barrels were packed with perennials and biennials, annuals could easily have been included initially to fill any open spaces until the perennials grew in.
How to do it
I can’t find very large whiskey barrels in Oregon, where I live, but the principle of a layered garden holds true for any stacked container. Here, 4-foot-square wooden boxes called filbert totes are readily available. They are about the same size as the largest whiskey barrel I saw in England and could easily be used as the base for other, smaller wooden boxes. They would be fairly easy to build or have built, or you could use large clay pots or other containers instead. Once filled with potting mix and planted, however, these container towers would be virtually immovable. To prevent the upper barrels from tilting as they rest on the soft potting mix, set them on concrete blocks placed in the center of the lower containers; plants and potting mix will hide the concrete support in the center.
If your container is to remain outdoors year round, wood is a good choice of container material. It moderates soil temperature extremes better than clay. Some of the very thick (1- to 2-inch) clay pots from Italy or the Far East seem to do very well for us here, but terra-cotta pots can flake and crack, so they need to be taken indoors or protected by placing them close to the house and under the eaves.
Use a commercial soilless medium augmented with coarse material such as perlite or pumice to enhance aeration and drainage. Never use plain garden soil; it won’t drain well enough. I find that a mixture of equal volumes of garden soil, perlite, and peat moss works well for a wide range of planters. Don’t put gravel in the bottom of the pot: that effectively shortens the depth of the pot and allows drainage only when the potting mix becomes saturated. Many container plants rot because of poorly draining potting mix.
Any container that you use for growing herbs must have adequate drainage; if holes are too small or too few, enlarge them or add new ones.
The size of the container will generally determine how many herbs you can grow in it. The plants’ restricted root zone can dwarf them to some extent, creating almost a bonsai effect and actually encouraging a longer blooming period for some plants. Prostrate rosemaries do especially well in containers, at least in mild climates, putting out their pretty blue flowers in late fall through early spring. The culinary sages and the more tender lavenders (Lavandula multifida, L. dentata, L. heterophylla) are also good performers in this type of container.
Container plantings require more care than a garden in the open ground. The contained plants are more vulnerable to seasonal temperature extremes and have no access to in-ground reservoirs of moisture and nutrients. You must provide it all–the watering, fertilizing, and general garden care. I prefer to use a liquid fertilizer at half the recommended strength every two weeks rather than using full-strength fertilizer once a month. This more uniform and constant application avoids a feast-and-famine cycle.
A tower framework
Another vertical plant arrangement that I’ve tried recently is a wrought-iron tiered plant tower that holds smaller pots. I had the opportunity to plant one with an herb garden for a fall apple festival. It was quite easy to have a finished herb garden in a couple of hours.
To hold the soil in place, I lined the tiers of metal ribbing with moist burlap and unmilled sphagnum moss that I had soaked in tepid water for about 15 minutes. Coir–coconut fiber–would have been an even better choice than the sphagnum moss: it lasts longer and drains well but doesn’t dry out as rapidly as sphagnum moss does, which may cut down on the frequency of watering.
For a cascading effect, I planted prostrate rosemaries and creeping thymes in the top tier. In the middle tier, I used a mixture of upright herbs such as ‘Tricolor’ and purple sages and a few of the more ornamental oreganos (Origanum rotundifolium and O. ‘Kent Beauty’), whose stems of pink-blush hoplike flowers are moderately cascading. The lowest tier contained the beautiful silver-leaved dwarf curry plant (Helichrysum italicum ‘Nana’), assorted scented geraniums, a bay and some tender salvias with unusual coral pink flowers (Salvia x jamensis). Altogether, I used about fifty plants; I would have used fewer if I had had more time for the herbs to fill out, but I needed this planting to look beautiful immediately.
The herb tower dries out very rapidly and requires daily watering. To make the best of this drawback, I chose herbs such as the ornamental oreganos and dwarf curry plant that require excellent drainage or that can tolerate drying out. Unlike the whiskey-barrel planting, this iron tower is movable. Two of us easily loaded it into a truck for delivery to the apple festival. I hung two baskets of the almost-everblooming bicolored Tasmanian violet (Viola hederacea) in its open center for added color and interest.
If winterhardiness is not a concern, some of the more unusual tender herb perennials would be excellently suited to a planter like this. Variegated society garlic (Tulbaghia violacea ‘Variegata’) provides season-long interest with its straplike foliage and umbels of pink flowers. It remains neat and tidy throughout the growing season, and its foliage contrasts beautifully with just about anything. Salvia patens has striking, inch-long flowers of rich azure blue that will attract many butterflies and bees to your planting. This species may be wintered over in a cool garage or greenhouse or grown as an annual.
Andy Van Hevelingen and his wife, Melissa, own an herb nursery in Newberg, Oregon. He has been a regular contributor to The Herb Companion for many years.