20 Aug 2014
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Watering the Summer Garden

Top picks for water conservation: careful planning, mulch to conserve moisture, infrequent but deep watering, and engineering that rainwater.

Watering the Summer Garden Watering the Summer Garden Watering the Summer Garden

Our big blue planet is the planet of water. Every form of life on our planet — from the largest mammal to the smallest microbe — depends on water. Without water, there is no life.  The amount of water on our planet is not infinite.

Sometimes we act as though this most precious substance is so ordinary we don’t even have to think about it.  

This spring it looked as though we were in for a parching drought.  Summer rains have brought our total rainfall almost up to the average (45” a year), but we are close enough to scarcity that gardeners are thinking seriously about the very best ways to conserve the water we use on our landscaping and gardens. 

That’s why the lush front garden at Melissa Braun Desjardins’s JP home is especially interesting. “No, we really haven’t watered at all this year,” the landscape architect assures me. “Of course the first year we had to water to get the plants started, but we’re in the third year now, and these plants are getting along fine with no watering.”

What is the secret to growing a garden that doesn’t need to be watered? According to Melissa, there are three important points.

First, proper planting design. The plants around Melissa’s house were chosen for their ability to be both beautiful and drought-tolerant. Many of these are native plants that are accustomed to surviving here in New England without extra care, or plants chosen because they do well in dry soil. ( The Weston Nurseries site offers lists of both native plants and plants that tolerate dry weather.)

Second is soil preparation, getting the soil ready to fully support the chosen plants.  Preparation may involve soil testing to find out about the health of your soil. A garden is only as good as the soil it grows in! Your soil may be low in nitrogen or phosphorus; if your soil is too sandy or too full of clay you may need soil amendments to get your soil ready to receive and hold water. Readers of this column will know that the soil amendment of choice here is usually compost!  

When you bring new transplants to the garden, you will want to stretch out the roots that have balled up and perhaps add some form of mycorrhizal fungi to help the roots get going. And you will want to water regularly until the plants are well established.

For trees you are adding to the landscape, you might be surprised at the amount of water you need to provide for the first year or two. For a tree with a one or two inch diameter near the base (landscape folks talk about this as the “caliper”), you should actually make sure the tree has ten gallons of water a week! One way to do that without overwhelming the tree is to dedicate a five-gallon bucket to the watering project; you make a couple of nail holes in the bottom and then set the full bucket (closed, of course) next to the tree. When it’s empty, you can move the refilled bucket to the other side of the tree. More on this kind of “spot watering” below.

The third element in creating a garden that doesn’t need to be watered is maintenance of your established garden. Weeds steal water from the plants they grow near. Melissa has found that as her plants have become well established, they have taken up more and more space so that there is less weeding each year, but she remains vigilant. A healthy layer of mulch does double duty by keeping down the weeds and holding moisture in the soil.

 

Mulch

When I asked eight different gardeners from JP how to conserve water use, seven of them mentioned mulch. The eighth, horticulturalist Jim Allen, specified good mulch, preferably pine or hemlock bark, rather than the cheaper hardwood mulch made from recycled pallets (the stuff that is often dyed orange or dark brown before being sold at the big box stores). 

Allen, a longtime JP resident and the head of the greenhouses at UMass Boston, gave an impassioned fulmination against the cheap mulch, pointing out that as it begins to decompose it leaches nitrogen from the soil around the plants it is supposed to be protecting, so you actually have to add some fertilizer with the mulch to make up for the damage it is doing.  And he argued that unlike the bark mulches, the cheap recycled pallet material can clump up and prevent water from getting through to the plant roots.

Some folks use black plastic to maintain moisture and keep out weeds (UGLINESS ALERT!). Bark mulch or shredded leaves are not only better looking, they also add organic matter to the soil as they break down. Here in Boston we can buy salt marsh hay to use as mulch. It looks charmingly rustic in a vegetable garden, and because its seeds need the action of the tides to germinate, it doesn’t introduce the kinds of weeds that compost can bring. (I first place four layers of newsprint down to keep the weeds out and help keep moisture in my vegetable garden, and then I pretty it up with salt marsh hay.)

And can you have too much of a good thing? Ray Dunetz, JP landscape architect, cautions mulch enthusiasts that more is not necessarily better: two inches is enough.

But wait a minute, we did get those summer rains. We don’t have water restrictions in Boston (the way they do in lots of towns around us). Do we really have to keep fussing about keeping the moisture in the soil? Why not just get out there and water? Isn’t part of the pleasure of gardening that you get to turn on your hose or sprinkler and watch the water flow?

I remember going to the community garden one beautiful summer afternoon. The day before there had been a long steady rain, and it seemed as though the air and plants had all been made fresh and lovely and the birds were just delighted, too. It was a great day for weeding because the weeds just slid out of the damp soil.

Along about mid-afternoon, this guy comes in to water his garden plot. No hurry about it, he is moving the hose back and forth in a leisurely way, watering the already rain-soaked plants. When I asked him what was up, he explains that watering his garden is a meditative experience for him.

Maybe it’s not so different from my memories of turning the sprinkler on for the kids on a hot day so they could run around the lawn screaming as the cold water hit them, the excess water running off into the street.

But you know, times have changed, and now we are aware that the supply of water is not infinite. Running the hose on full for ten minutes uses some 200 gallons of water.  Running that excess water down the storm drain, or watering the garden when it doesn’t need it or on a hot or windy afternoon when a lot of the water is going to evaporate just doesn’t make sense.

 

Deep, infrequent watering

Now as Melissa pointed out, there are times when you have to water (when new plants are getting established, when there are plants in containers, and when you are growing plants that are flowering or fruiting that need a regular supply of water to develop properly). The question is how you do this watering.  Here are some pointers

  1. Deep, infrequent water should be the rule. Don’t give in to the temptation to water every hot day! You will be teasing your plants into growing their roots toward the surface where they can catch your little daily drinks. Test soil dryness and water only when it is needed.  That probably means pulling out a weed and checking the soil around its roots or sticking a tool down two inches or more – that will give you an idea of the moisture content of the soil.  It should get dry between waterings.  The fancy drip irrigation systems have a device that gauges when the soil is dry enough to trigger a watering. You’ll get a feel for doing the same thing.
  2. Water the roots, not the leaves of the plant. Excess water on the leaves can lead to some plant diseases, and anyway, it’s the roots that are going to get the most out of the watering. A good way to get the water to the roots is drip irrigation. You can provide that with a drip irrigation hose or system of hoses, or you can provide it by “spot watering” specific plants with the old plastic milk container method: you make some pinholes at the bottom of the milk container, bury it up to the neck near the plant you want watered, fill up the container, and let the water do its work, trickling out of the container a little at a time to give the target roots water.
  3. The best time of day to water is early in the morning (it also makes you feel virtuous to be out there with the birds, giving your plants a drink as you greet the day while people in the houses nearby are still just slowing around). If you wait until a hotter time of day, a lot of the water gets evaporated before the plants get to use it. It’s like watering on a windy day; you don’t get the water where you want it to go. For some folks, evening is the only available time. Okay, but avoid watering on very humid evenings, because leaving water on the plants overnight in very humid conditions can invite the development of fungi and disease.
  4. If you going to use a hose to water, use one with a hand-held shut-off mechanism so that you are only running the water when you need it. Learn the pleasure of a water wand, which allows you to tuck the hose under the leaves and get it right at the roots without crouching down. (When I asked JP garden educator Erika Rumbley about conserving water in the garden, part of her response was to act out holding a water wand in under the leaves to the roots of a plant).

 

Collecting rainwater

A final way to cut down on our use of city water resources is to use rainwater, either by collecting it in rain barrels for later use or by engineering the downspouts that carry the rain off your roof to the plants that need them. (See the attached picture of the extension on the gutter from Melissa’s house, which provides rainwater to a shrub that needs more water than the rest of the garden). 

Boston Building Resources can help you learn how to install a rain barrel (and make it mosquito proof) so that you can conserve our precious resource, water.

 

P.S.— Lawns need an inch of water a week to stay green. Old-timers set out a tuna fish can to measure the rainfall to see if there has been enough water, and then if it’s needed, set the sprinkler carefully to cover the lawn. Thing is, even if it’s really dry and the tuna fish can is empty and your lawn goes totally brown, the grass is not dead. It’s just hibernating, and at the first real rain it will come back to fully green life again. And think of the water you’ve saved!

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