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Monday, October 3, 2016

Rain at last!

Whoopee! I’ve returned from a vacation in dry and sunny Italy

Ah, Venice . . .

to find that the Boston area had almost an inch of rain while I was away. It’s amazing how different the garden looks with just that much welcome refreshment.

Wet at last

     The lawn has turned green again, and in containers and beds plants are looking peppy, shedding their tired late-summer appearance. It helps that some fall color is starting to show. Fall-blooming flowers are beginning their display. The whole garden scene is a lot more encouraging.

Japanese maple leaves starting to turn red

    How long will this last? Occasional showers are expected into next week as a storm system gradually moves away. We heard predictions of possible showers all summer, though, and most of them either didn’t occur or dropped only light sprinklings that wet the leaves without seeming to moisten the soil. We haven’t seen sustained rain like Saturday’s in a long time.

    Can’t leaves absorb moisture even if sprinklings of rain don’t make it to the ground? Some water can get in through the stomata, pores that open to allow water out of leaves under non-drought conditions. That’s enough to reverse wilting temporarily. I suppose it’s one reason for creating a humid environment around our house plants with misting or pebble trays.

Ornamental grass flower holding water droplets

     But leaves of most plants can’t take in enough moisture to replace water from soil. Come to think of it, some of those house plants originate in the cloud forest, where absorbing water through leaves is a more common adaptation. New England natives need to get their water from the ground.

Even huge leaves of elephant ears can't absorb all the water the plant needs

    Last week’s inch of rain permeates the top twelve inches of soil. My sandy loam takes in water easily, but it also lets water flow through quickly. Sand holds water by capillary action, the way a sponge or a paper towel does. As water drains through sandy soil, soil moisture drops to the wilting point, the proportion at which plant roots can’t extract water they need. We saw that happen over and over again this summer.

Hydrangea at the wilting point

    Soil water retention is one reason that adding organic material such as compost is so important. The chemical properties of organic material enable soil to hold more water for longer because of adsorptive forces that surround soil particles with a film of water molecules. 

    I hope that compost and leaf litter—leaves decomposing in place when I didn’t rake or blow them away—are giving my plants a chance to take advantage of this long-awaited rain. If these soil builders just lie on top of the soil, at least they’re preventing evaporation, holding moisture in the soil for longer than if it were bare. 

Compost to the rescue!

    Incorporated into soil by organisms ranging from fungi and bacteria to nematodes, insects, and earthworms, the organic matter does even better. The organic particles hold water near the surface where roots can drink it in. Cheers, Salud, and L’chaim!

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