Planning and Planting the Dry Garden
The lovely rain is so welcome that I can hear neighbor kids laughing and singing as they run in the refreshing wetness. Although our Northwestern summers are typically very dry indeed, this year takes the prize for heat and drought. Though some folks struggled to deal with water restrictions, the good news for gardeners is that limiting water use need not spell garden ruin nor even deprivation. Sensible plant choices and intelligent watering techniques will help keep our gardens healthy and attractive no matter what next summer brings.
However, a few changes in our usual methodology may be in order. If you are renovating a bed or just beginning to garden, consider adapting dry garden techniques that have proven highly effective (and handsome) in England and elsewhere. Dry gardens are based on well chosen plants that can thrive with relatively little input from the gardener. Typically, they hold a mixture of natives and allies from other parts of the world with similar weather patterns.
How To Make It Work
In brief, here are the basics of dry garden construction:
* Build mounded beds for good drainage.
* Make the beds big enough to function efficiently.
* Mulch generously with compost and/or gravel.
* Pick the right plants for your site.
Though simple, these key points require some explanation. For example, mounded beds are not the same as raised bin-beds with wooden or plastic sides. They are just what they sound like; mounds of good garden soil. Mounded beds don’t need to be any higher than 18 inches, but may be as much as 2-3 feet high in areas where varied topography would be appropriate.
Making beds big enough is partly a matter of efficiency and partly a matter of scale. Even in a small garden, build beds as boldly as possible, so the landscape works with the scale of the surrounding home and neighborhood or woods. Think big and think simple; strong shapes and clean lines will always read better than little ditsy beds that make a garden look like a miniature golf course.
How big is big? Depending on the size of your property, beds may be any width from 4 feet to 40 feet. Little strip beds rarely function well (and look well even less often), so the length should be similarly bold. If you are adding large rocks to your landscape, the mounded beds should be scaled with appropriate generosity. Where there isn’t room for beds this size, pave or gravel the area and use big, abundantly filled containers instead.
Let The Soil Breathe
Mounding the beds offers plant roots breathing room and prevents winter rots, especially on heavy clay soils. For optimal results, think in terms of cubic yards of topsoil and compost, not a few little bags. Look for topsoil mixes that combine sandy loam, compost, and clay-based soil. In the Seattle area, I recommend Cedar Grove’s vegetable garden mixture, which works very well for mounded beds.
Mulching with blankets of organic material makes plants less vulnerable to fluctuations of temperature and drought. In most cases, an annual 2-4 inch mulch of mature compost is enough to keep weeds down, keep moisture in, feed soil, and look attractive. In the dry garden, drought tolerant plants are planted and mulched with mature compost, and are often top mulched with crushed gravel.
Going With Gravel
Gravel mulch pleases many drought loving Mediterranean plants, from lavender and rosemary to grapes. Though we don’t think of grapes as drought loving, in the Loire valley of France, the grapevines in the famous vineyards are mulched with the local honey-colored stone and never watered. Indeed, vintners are disallowed the use of their appellation if they are caught watering the vines; the result won’t be true to type.
Similarly, French lavender and Italian tomatoes are grown with very little water, especially as they begin to ripen flowers and fruit. Excess water reduces the quality of the essential oils in herbs and makes tomatoes flabby and bland. If you decide to experiment with gravel mulches, always use crushed gravel. Neither rounded pea gravel nor river rock will function properly as plant mulch. In most cases, a top mulch of gravel will be an inch or two deep, but in some cases (as with the grapes), stone chip or gravel mulches may be 3-4 inches deep.
Recognizing Watering Needs
To choose the right plants for your site, identify what kind of site you have. The primary question to ask is whether the site is sunny or shady. Most dry garden models are for sun loving plants in sites with plenty of light, but shady dry gardens are also possible. (I’ll write more about this soon.) When choosing plants, consider that as long as your garden soil is well amended with compost, many ordinary garden plants, from shrubs and perennials to grasses and vines, will flourish with very little water once they get established.
You will need to water youngsters regularly (probably weekly) for the first year or two, but they’ll need little or no water after that. There are exceptions of course–roses and clematis leap to mind–but a look at neglected neighborhoods shows clearly that many established plants can carry on without help for decades.
Learn When To Back Off
If you’ve been routinely over-watering your plants, they will have very shallow roots. This makes plants less resilient and highly susceptible to stresses of all kinds. The key to plant and garden sustainability is good root growth. To encourage deeper root growth, mulch generously with compost, and do it during the wet season, while the soil is still damp.
Next, adjust your irrigation habits. If you are in the habit of watering daily, that’s important for container plantings, but for gardens and lawns, switch to weekly watering (delivering about an inch at a time). Some irrigation companies tell customers to irrigate lawns twice a day. This is just plain wrong. To encourage your lawn to grow deeper, healthier roots, rake in about half an inch of compost each autumn and early spring and irrigate no more than once a week. As your turf gains better roots, it will also gain resilience to the pests and diseases that plague over watered lawns.