Watering — in the Rain?

Why Are Pots Thirsty?

With recent rains of more than 3 inches over the last couple of days, you’d think that the last thing on my mind would be having to water anything. But you’d be wrong. Plants in pots — and I have plenty of them, some ornamental and some tropical and subtropical fruits — don’t get the full benefit of all that water.

Potting soils are, and should be, more porous than any garden soil to maintain good aeration within the confines of a pot. About a one inch depth of water is needed if you’re going to thoroughly wet a 12 inch high column of potting soil. If a flower pot is, for example, only 6 inches high, only 1/2 inch depth of water would be needed; and so on.

A lot of my potted plants didn’t drink in that 3 inches of rain that fell over the past couple of days. Some of the plants are shielded from the sky by overhanging house eaves. And the leaves of other plants — excepting amaryllis and calla lily which have strappy, upright leaves — deflect water that could have fallen into the pot.

If you don’t believe me, tip a potted plant out of its pot following a heavy rain, and check how dry the soil is down deep within the pot. Even easier, purchase an inexpensive moisture meter whose metal probe, when slid into the soil, reports moisture deep down.

(Sort of) High Tech Solution

When I first started gardening, I knew I would eventually move from the cottage I was renting. My mini-orchard was in pots and travel-ready. I kept that “orchard” watered by hand, which wasn’t so bad. The problem was that in the heat of summer, some plants needed their thirst quenched twice a day, which kept me from leaving my home for more than a few hours.

These days, technology has come to the rescue.

The first techno-solution has been drip irrigation. A simple, battery-operated timer at a spigot sends out water on a twice daily schedule to banks of potted plants. Also at the spigot, following the water line right after the timer, are a filter and a pressure reducer. automatic watering, potsThe fittings for wending water through tubes around corners and up into pots are low pressure fittings; the pressure lowers water pressure to a mere 20 psi.

Once the 1/2 inch main line makes its way to a group of potted plants, a 1/4 inch plastic line, plugged into the main line with, of course, a low pressure fitting, carries the water up to the ground surface of each pot.

If the water merely exited at this point, pots closer to the water source would be under higher pressure and so get more water than those more distant. And pots that were shorter or at lower elevation would likewise get more water. So I slid an emitter, that reliably puts out 1/2 gallon of water per hour, no matter what the incoming water pressure, on the end of each 1/4 inch line.

Capillarity to the Rescue

I have a number of lowbush blueberry, lingonberry, hollyhock, carnation, and blazing star plants growing in pots 4-inches and smaller. I’ll eventually plant them out in the garden. Until then, the plants need regular watering Snaking 1/4 inch tubes to all these pots would create a tangled nightmare.

Enter capillary mat watering. All these smaller pots sit on a mat of absorbent fabric spread over a tray held a couple of inches above a pan of water. Irrigation, capillary matPart of the capillary mat dips into the reservoir of water, which gets sucked up into the mat and then sucked up into the potting soil through the drainage holes in each flat-bottomed plant pot.

I periodically have to remember to add water to the reservoirs. Or, rather, “had to” because I ran a few of those drip tubes into the reservoirs, enough to keep them topped up with water to keep pace with plant use.

And a Presentation of Interest

I’ll be doing a presentation on August 18th on THE SCIENCE, ART, FUN, AND TASTY FRUIT OF ESPALIER in Copake Falls, NY. The presentation will explore the theory and the practice behind the pruning and orienting of branches to create an espalier. This decorative, usually 2-dimensional form, offers high yields of high quality fruit on a plant or plants that can be free-standing, decorating a wall or fence, or even creating the fence itself! I’ll go over which fruit plants work best and the branch pruning and orienting techniques that create and maintain espaliers that look good and yield especially delectable fruit. For more information, go to pear espalier flowering


It Mite be a Pest

    Mites! Eek! A new pest in town (for me). Actually, the mites, which showed up on some newly rooted Meyer lemon cuttings, don’t really scare me, nothing like the scale insects that regularly turn up on some of my citrus. Chigger mites, scabies mites, dust mites, itch mites — they’re not pests of plants, and they WOULD scare me.
    The cuttings were well rooted and just sitting still, basking in a south-facing window, waiting for longer days and warmer temperatures before they can come alive. (They pick up an attenuated version of seasonal temperature changes at that window.) A few weeks ago I noticed a yellow stippling developing on the green leaves.Mite damage symptoms
    No panic; the plan was to wait a few weeks and see if the stippling disappears or if new growth, unstippled, develops. Citrus sometimes develop iron deficiency, which also yellows leaves, in cold soils, not because the soil lacks sufficient iron but because the roots aren’t at the top of their game in cold soil.
    A closer look a few days ago revealed, to the naked eye, very small black specks on the leaves. An even closer look, with a hand-held lens, revealed tiny mites crawling around on the leaves.
    Mites are mostly problems in dry, dusty conditions, not atypical for a house heated in winter and the usual for summer in Mediterranean climates such as California. One simple cure is to make conditions less dry and dusty. Climate change within the whole house would be impractical. Instead, I started giving the plants a daily spritzing with water.

Mites, photo with iPhone + hand lens!

Mites, photo with iPhone + hand lens!

   More potent sprays may be needed; fortunately they need not be toxic to humans. “Horticultural oil” sprays are effective as are sprays of insecticidal soap. Problem is that these sprays are inconvenient to use indoors, where excess spray would end up on windows, furniture, and floors. Sprays need to be repeated weekly to kill mites that hatched from eggs (which are spray resistant) since the last spray.
    Because the Meyer lemon cuttings are still small with very few leaves, I chose to go at them mano a mano, merely rubbing my fingers across each leaf to crush the buggers (technically arachnoids, like spiders, not bugs). As with the oil or soap sprays, mano a mano combat must be repeated to crush newly hatched mites. But it’s quick and satisfying.
    Mites do have many natural predators, among them other kinds of mites. Just like Jonathon Swift’s flea that “Hath smaller fleas that on him prey; And these have smaller still to bite ‘em; And so proceed ad infinitum.”

Low-Tech Auto Water

    Every couple of days I have to think of all the plants in the house (they’re not all “houseplants”) that need water, including the mite-infested Meyer lemon cuttings. Two devices or setups keep me sane and my plants healthy in the face of all this watering.



    Larger, potted plants — those in pots over about 4 inches in diameter — are serviced by “water siphons” (aka “hydrospikes”, “self-watering probes”). A porous ceramic probe, previously soaked in water, filled with water, then capped, is pushed into the potting soil. The far end of the long, thin, flexible tube that comes out of the cap is plunked into a reservoir of water. I use mason jars as reservoirs and pre-fill the tube with water so that the water column is continuous from the ceramic probe to the reservoir.
    Voila! As the potting soil dries out, it sucks water from the ceramic probe which sucks water along the tube from the reservoir. Larger pots need more than one ceramic probe.
   Capillary mat For smaller pots, I use capillary mats, which are nothing more than water-absorbing mats (available from on which sit the pots. The mat is laid on a stand that sits above a similarly shaped, one-inch-deep tray, with one end of the mat dipping down into the tray. The mat absorbs water from the reservoir and the potting soil in the pots, as they dry, absorb water from the mat.
    It’s important to maintain good capillary contact between the potting soil and the mat. This means no coarse drainage material in the bottom of the pots (a silly, counterproductive idea anyway), and no “feet” elevating the bottom of the pot.
    Not having to frequently water makes it all too easy to forget about watering. I already lost one old rosemary plant this winter. Hydrospikes and capillary mats don’t work — duh! — unless their reservoirs have water in them.