Thursday, August 23, 2007
I have found myself watching the weather maps in the hope that a great, swirling cotton candy monster called a hurricane will come my way.
Not as a devastating storm, but something weakened and wet that will sit over the mid-Atlantic and quench the thirst of prized garden plants parched from a summer of dry heat.
Two, three or four inches of rain should do it. That may prevent further needle drop from the dawn redwoods, perk up the flagging viburnums, top up the lily pond and get the stunted ornamental grasses to burst forth, finally.
Storms are hit-or-miss, so I keep a screwdriver handy. This simple household tool is perfect for measuring how wet the soil is after the gardener or Mother Nature irrigates it. In spite of a slight break in the weather pattern this week, that chore has fallen to the gardener this summer. A screwdriver will descend cleanly through wet soil but will not penetrate the dry level beneath. If you can get the shaft to sink four inches, you have done a good job of watering, and you can then leave an area alone for a few days or more.
Achieving good soil saturation takes a variety of watering techniques, some better than others.
Automatic irrigation systems have their place, especially for people who travel a lot or have gardens at second homes. I fear them for reasons beyond their cost, which can be formidable. I have seen them kill plants by overwatering. Moreover, they tend to take the human out of the equation, enticing us not to check on our plants and enjoy them, which seems to defeat the purpose.
If you want irrigation on the cheap, hook up a soaker hose to your garden hose. The hose has thousands of pinholes, and the water oozes out slowly over several hours. In theory, this seepage delivers moisture to plant root zones in an efficient way.
In my experience, soaker hoses are fine over short distances and on flat ground. They work well on certain vegetable crops that are in the ground for much of the season, such as tomatoes, peppers and squash. But string two or more 50-foot lengths together and employ them over hilly ground, and you will be disappointed. Water will seep from the first few feet but offer a mere teardrop or two farther from the spigot.
Here's a fact to impress your friends: For every 2.3 feet a hose rises, the internal water pressure drops by one pound per square inch. "If you start on low ground with 10 psi and go up around five feet, you're going to have 8 psi," said David S. Ross of the University of Maryland's Department of Environmental Science and Technology. "That's a 20 percent variation in pressure there."
A more refined version of the trickling hose is found in a drip-irrigation system. Water, pressure-regulated and filtered, is sent to a pipe that feeds emitters -- small lengths of mini-hoses positioned to deliver water to individual plants.
Produce growers use these beneath plastic mulch as an effective way of defeating summer droughts like this one. The plastic traps the moisture and prevents weed competition. The same system would work as well for homeowners but would need to be put in place at the start of the season, in May, and would not be suited for a lot of root vegetables such as carrots and onions. Also, this setup requires a raised bed to prevent rainwater puddling on top of the plastic mulch, said Jerry Brust, another agricultural expert at the University of Maryland.
If you didn't want to fuss with the plastic, which needs pinning in place, you could use a straw mulch. But Brust recommends a thick four-inch layer because weeds love drip-irrigation systems and would quickly smother your desired plants. Drip irrigation also works in ornamental beds, but the difficulty there is that if you are constantly planting and replanting them, as I am, you would live in fear of slicing through the lines.
Still, the drip method is the most efficient way to water and prevents foliage diseases associated with overhead watering.
Sprinklers, either oscillating or the impulse type, with a pulsating head, are useful for watering for extended periods to recharge the ground. Setting out sprinklers in the early morning will be more efficient than in the heat of the afternoon, when you could lose as much as 30 percent of the water to evaporation, Ross said. The constant challenge with sprinklers is getting a pattern that will reach awkward corners of the garden without dousing paved areas and wasting water. Another challenge is to get the sprinkler head above shrubbery, a problem solved with a sprinkler tripod.
A time-honored way of rehydrating trees that have suffered from drought is to lay an open hose in the root zone and let the water trickle. The older the tree, the farther the feeder roots are from the trunk. These fine roots, used to take up moisture and nutrients, can extend well beyond the drip line of mature trees, so don't lay the hose right next to the trunk. If the tree is on a slope, place the hose on the high side. If the water is running off, the flow is too strong. Once you have the flow right, leave the hose for a couple of hours at least. You don't need to move the hose around the zone; a partially saturated root zone will fully hydrate the top growth of a tree or shrub.
Hand watering, done correctly, is the best way to water plants because you deliver a lot of water precisely where it is needed. Ross cringes when he sees people using a spray nozzle and giving a rapid, daily watering of garden plants. This doesn't soak the soil but merely wets the upper surface, which encourages plants to grow surface roots that quickly dry out. It also provides perfect conditions for slugs. Far better to soak the soil (have that screwdriver handy) and water only once or twice a week.
Put away the spray nozzle and either use your thumb to squirt water from the open hose or, better yet, buy something called a watering wand. This has the capacity to deliver large amounts of water but in a gentle spray, without washing away soil or mulch. See a hydrangea wilting? No problem: Spend a minute directing the wand's fountain to the leaves and the roots, and it will perk up in no time. Hand watering takes time, but there is a Zen-like quality to it.
There is still a time and place (in my garden at least) for the old-fashioned watering can. Anything with at least two gallons of capacity will quickly water containers, lettuce seedlings and patio trees, for example.
It speeds the chore, it should be said, if you have a fish pond handy, as I do. I dunk an old galvanized, four-gallon watering can in the water and go to town on all the plants on and around the patio.
Earlier this summer, I was following this morning ritual when the water suddenly dried up. I removed the perforated spout, called a rose, to clear what I thought was a leaf clog, only to find the head of a goldfish sticking out of the tapered tube.
It is hard to say who was more alarmed. But I kept my cool and gently poked the fish back into the can (submerged in the pond at that point). Sorry, my fishy friend. It has been a tough summer all around.