Water-Wise Gardening

Golden strawflower (Xerochrysum bracteatum) with ground cover growing in a floating island planter. Photo: Dick Schuck, Maryland Aquatic Nurseries Inc.

Container gardens add great beauty to courtyards and terraces. They’re a triple aesthetic threat because in addition to beautiful plants there is the sculptural interest of the pots themselves plus the spatial complexity derived from using containers of different heights. As an ensemble they can make a small space look larger and more sophisticated without actually having to build anything.

The downfall of container gardens is our local climate. Unless an irrigation system is in place, you can return home from a day’s work to find a mass of droopy, dried-out foliage demanding immediate attention precisely when you most want to relax and enjoy the garden.

Even with irrigation, DC water has additives that can compromise plant health. They include chloramine, a combination of ammonia and chlorine. Chloramine is not safe for fish, so if you have a small backyard fish pond you will want to either collect roof runoff in a rain barrel or treat your tap water with an additive. DC also adds fluoride to the water supply, which can harm certain kinds of plants. Here’s a fact sheet put out by the DC Water and Sewer Authority: https://www.dcwater.com/waterquality/faqs.cfm.

Water is also becoming costly. Because the District must pay its fair share of the estimated $20 billion needed regionally to fix outdated water and sewer systems, DC water rates have doubled in the past six years. Last year alone, rates increased 13 percent, so that a family of four now pays an average of $96 a month for water. Rates are set annually, so expect upward trends to continue.

Given the cost, efficient watering makes good economic sense in addition to helping the environment through conservation. This is true for all gardens, not just containers. Here are some innovative products that will help make you and your plants water wise this season.

Plant Life Rafts

Dick Schuck of Maryland Aquatic Nurseries has developed floating planters that act like rafts. Each one, made of durable UV- and water-resistant polyethylene, is a ring with an opening for a plant liner. The plant goes into the liner, which has small holes in the bottom and is filled with a special buoyant grow mix. As long as the container it sits in holds water, plant roots have non-stop access to the moisture and nutrients they need. If the foliage growing in it covers the opening at the top of the container, mosquitoes cannot breed, and the water in the planter will not evaporate quickly. If you collect any rain water, that should be all you need to periodically top off the water level.

Available at local garden centers (especially by request), these plant rafts (or “flotation collars”) come in single liner sizes ranging from 5 inches to 24 inches in diameter, and in a sundial configuration that has one larger center plant holder plus four smaller ones around it. If you own some containers, measure them before ordering to be sure your plant life raft will fit inside. (I didn’t do this, so now I either need a larger container or a smaller raft.) While the unplanted raft isn’t easy on the eyes, within weeks your floating plants will cover the black foam and you’ll be in business.

The recommended potting mix comes in two bags, one with the soil media and another with the buoyant clay particles. You layer them so that the clay is in the middle like Oreo cookie filling. Although this system is ideal for aquatic plants, even carnivorous ones, folks have reported success growing most garden plants including edibles and herbs. The mint family (Lamiaceae) will be happy in this environment, including basil, bee balm (Monarda), cat mint (Nepeta), mountain mint (Pycnanthemum virginianum), rosemary, sage, and lavender, plus peppermint, spearmint and watercress. I would think that parsley, coriander, dill, spinach, lettuce, and chard would also be winners in this type of planter.  

Ornamentals to try would include blue flag iris (Iris versicolor), yellow flag iris (Iris pseudacorus), elephant ear (Alocasia), Canna lilies, coleus, ferns, and tropicals like ginger (Hedychium).

Hydrogels

Broadly speaking, polymeric hydrogels are natural or synthetic chemical structures capable of holding large amounts of water in their three-dimensional networks. First developed in the 1950s as wound dressings, they have found their way into the green industry as soil additives intended to increase water retention, making moisture available to plants slowly and evenly.

Found under brand names such as Terra-Sorb and SoilMoist, when used in pots or garden beds they can moderate moisture availability in a plant’s root zone. They are not a substitute for water, nor will they make a shade-and-moisture-loving plant like impatiens happy to live in full sun.

Follow directions for plant hydrogels. More is not better, and you will be surprised at how little the directions on the package say to use. My one-pound container has lasted for years since only one teaspoon is sufficient for a one-gallon pot. Be aware that there are natural and synthetic hydrogels. There are gardeners who will not use synthetic ones, not liking how the polymer structure breaks down in the soil. You are best to do your own research and review what’s called each product’s MSDS, or material safety data sheet. These products are available at local garden centers.

Ultra-Low-Maintenance Grass

Usually I discourage lawns for Hill gardens, but if you want a lawn, you should grow the most environmentally friendly grass available. That would be Pearl’s Premium Ultra Low Maintenance lawn seed. I seeded an 800 square-foot test plot in mid-October and the results are astounding. Granted, we have just set a record for the longest string of rainy days ever, but this grass is soft to walk on and grows very slowly. It also “seldom or never needs water once established” according to founder Jackson Madnick (whom I have personally met), and it needs to be cut only once a month – or never if you learn to like a soft floppy grass.

Another benefit of this grass, and one reason it is so successful, is its deep roots. They help crowd out weeds and also retain a greater volume of stormwater than traditional turf. Pearl’s Premium is patent-pending for its precise proportions of grass seed, which, Madnick explains, makes it work so well. I count 11 types of fescue, rye, and bluegrass in the ingredients on the back of my five-pound bag. As with hydrogels, the product’s application instructions should be carefully followed for greatest success.

More Plants, Less Mulch

One last water-wise garden tip that might seem counter-intuitive is to plant more densely. You might think that more plants would require more water, but in fact widely spaced plants with expanses of mulch in between dry out the soil more quickly plus encourage weed seed germination. Your densely planted beds will create a leafy canopy that retains soil moisture and prevents weed seeds from landing on receptive ground. Learn to divide perennials planted three years ago or more, and you’ll find that you have plenty of plant material to go around. I just created 10 Husker’s Red Penstemons from the one I bought a few years ago. Divide and conquer your plant beds as one more water-wise gardening tool in your kit.

A 24-inch plant raft with potting mix ready to go. Photo: Cheryl Corson
Black taro (Colacasia “Black Magic”) in a floating island planter. Photo: Dick Schuck, Maryland Aquatic Nurseries Inc.

Cheryl Corson, RLA, ASLA, is a landscape architect and dirt gardener practicing on Capitol Hill and beyond. www.cherylcorson.com


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