Thursday, June 16, 2011


            This morning, Oak Island got .16” of rain. It’s the first significant accumulation since May 20th. Today we start a series on watering and water in the garden. 
My rain gauge,
late morning 14 Jun 2011:

The two basic ingredients for gardening success are soil and that most precious of natural resources, and the one most Americans take for granted, water. Where I live, we’re awash in it—the Atlantic Ocean, the Intracoastal Waterway, sounds, bays, inlets, river mouths, estuaries, great tidal marshes. Coleridge’s Ancient Mariner has our number, though: most of the surface water is too salty to be potable for people or plants. As local population continues to burgeon, fresh water supplies will become increasingly problematic.

Well, you counter, temperate climates get lots of rain. That’s true, between 30 and 65 inches a year on average (not including the desert Southwest and the Olympic Peninsula’s rainforest). But ask anyone who lives in the Midwest, or Texas, or Florida: you can’t really count on it falling in gentle showers amounting to about an inch a week.

In one fabled week back in 1999, Hurricanes Dennis and Floyd deposited 40-plus inches of rain on southeastern North Carolina. While that number verges on apocryphal, it still serves as an example of how precipitation precipitates out around here. Yearly rainfall totals on the Atlantic and Gulf coasts depend on tropical systems, and they are notoriously unreliable. We haven’t had such a dousing since Floyd. And we've been in drought to some degree or another since then, too. 

Sand all the way to China
on Oak Island
(this is our neighbors' yard,
not the beach)

Even in good years, there’s still the factor of the near-instantaneous drainage of sand: just because 1.37 inches fell into your rain gauge Monday evening doesn’t guarantee your plants will have anything to drink by Wednesday afternoon, particularly in high summer. Aquifer replenishment doesn’t necessarily translate into readily available moisture in the top eight to 12 inches of soil. And, if your yard has one or more mature trees, their extensive root systems commandeer a lot of what water the soil manages to hold on to.

Sandy or not, the type of soil you have matters, because particle size influences how water enters and percolates through plants’ rooting zones. Sandy soils permit water to penetrate and drain away more quickly than fine-particled silts, clays and humic soils, or compacted soils like caliche and swamp muck. (“Caliche” refers to the calcified soils of much of the arid American Southwest.)

Shredded cocoliners recycled
from last fall's hayracks
make great mulch
A garden is by definition a managed environment, so take the trouble to design (or reshuffle) your landscape with efficient water use in mind. Position plants with similar moisture needs together. Keep a two to three-inch layer of organic mulch in all beds and borders to help hold in moisture and keep roots cool(er). Fine-bladed grasses like Bermuda and Zoysia handle drought well. The roots of broader-bladed centipede and St. Augustine grasses survive dry seasons as well as Bermuda and Zoysia; they just look awful on the surface, reacting to drought by turning a dull greeny-grey color and rolling their leaves into what look like tiny cigarettes. “Real” grasses—cool-season fescues, ryes, blue- and bent-grasses—dislike drought intensely, and may experience die-off.  


Drought-stressed centipede grass
chez Fitzgerald

Non-drought-stressed centipede grass
chez Fitzgerald


A mesic trio:
plumbago (Plumbago auriculata),
black-eyed Susan (Rudbeckia hirta) &
Texas sage (Salvia greggii)

           Choose plants known to tolerate drought. Once established in the landscape, trees and shrubs like abelia, butterfly bush, crape myrtle, eleagnus, junipers and big- and small-leafed hollies do quite well for long periods without supplemental irrigation. (Berrying hollies won’t set as much fruit after a dry season, though.) Many perennials and annuals—annual vinca, aster, black-eyed Susan, blanket flower, butterfly weed, catmint, coneflower, gazania, globe thistle, ice plant, lantana, liatris, plumbago, salvias, Stokes’ aster, sunflowers; most anything with thick, waxy leaves like sedums and succulents; fuzzy foliage like lamb's ears or artemisia; very tiny or needle-like leaves like Serissa and Amsonia hubrictii—have mesic (requiring moderate amounts of water) or xeric (requiring very little water) qualities: hydric plants require heavy and frequent hydration. Generally speaking, xeriscapes are most often found in arid climates like the Southwest and high-altitude locations. Coastal areas are mesic because we get too much rain to be considered xeric. Thank goodness.

Mesic long-leaf aster
(Aster oblongifolius)

A xeric-once-established trio:
catmint (Nepeta x faassenii),
ice plant (Delosperma cooperi) &
lantana (Lantana montevidensis)

As demands on fresh water sources increase with population growth and the extravagantly wasteful habits of many Americans, planting and maintaining mesic- and xeriscapes become the only reasonable alternatives for sustainability-minded gardeners. 

This droopy coleus alerts me
to low soil-moisture

Learn to recognize early drought-stress symptoms; wilting, caused by transpiration (loss of water through leaves), and marginal leaf burn are the most recognizable and common. I always include “indicator” plants in the gardens we design, ones that provide timely warning of soil dryness. Coleus works especially well in this capacity; so do Shasta daisies and hydrangeas.

Paradoxically, too much water is just as bad as not enough. Without delving too deep into soil science, suffice it to say that both cause imbalances between air and water in the pores between soil particles. That’s why the wilting and leaf damage look exasperatingly alike whether the plant is drowning or gasping for water. Conduct the finger-in-the-ground test recommended below before taking remedial action.

The bottom line of supplemental irrigation is the achievement of a one-to-one ratio between the amount of water a plant needs and what it actually receives. Which brings us at last to the crux of this whole watering issue—even if you have a perfectly installed and vigilantly programmed and maintained irrigation system, you still need to pay attention

Tim finger-testing
the soil moisture in our
Tibouchina grandifolia
(the rain barrel in the background
is a teaser for next time) 

Begin by taking the time to understand the drainage properties your yard's soil. Watch the weather. (While it’s always amusing to see someone’s sprinklers running during a cloudburst, it’s not really funny, conservation- or plant health-wise.) Don’t assume that just because fall rolls around you're off the watering hook until April: in southeastern North Carolina, October is statistically the driest month of the year, followed by January. Find out the general water requirements of the plants in your yard, and group those with similar needs together. Most important of all, to ascertain whether or not you need to add water, go outside and stick your finger up to the second knuckle into the ground and check out how moist—or not—it feels. Then act accordingly. Get into the habit of really looking at your plantings and finger-testing your soil: you’ll have a better chance of spotting and addressing water problems before fatalities result.

There’s not a lot of information out there about how to best water lawns on sandy soils. Most sources advocate infrequent deep watering, which sand makes impossible. An inch a week is the rule-of-thumb recommendation; you’re advised to place empty tuna cans at various spots around the yard to measure how much water gets dispensed from the sprinkler or irrigation spray-heads. That’s ’way too much like work for me. I rely on watching the weather, scouting my plants for drought symptoms, and the stick-finger-in-dirt method to ascertain if I’m watering prudently.

A Water-Wise Quiz
1.      Do you keep the tap running while you brush your teeth, shave, or wash the dishes?

2.      Run the dishwasher (the machine, not the person) and/or the washing machine before they're fully loaded?

3.      Shower for longer than five to seven minutes and/or run the water while you’re soaping up and shampooing?

4.      Have dripping faucets inside or hose-bibs outside?

5.      Hose off your sidewalks, patios and driveways instead of sweeping them?

6.      Wash your car often?

7.      Have a leaky or poorly maintained swimming pool?

8.      Turn on the bathroom tap so the spoiled-rotten cat can get a drink but neglect to turn it off as soon as the young prince has finished? Tim? Sally?

9.      For those of you with in-ground irrigation systems: Do your spray heads water the house, driveway or road?

10.  Have you run the irrigation system during or just after statistically significant rain?

If you answered “yes” to any of the above, stop doing it/them right now.


Next time: a colloquy on in-ground irrigation systems. Thanks for dropping by. Stay hydrated.