Friday, January 31, 2014

Deeply Irrigating in Response to Drought Emergency -- am I mad or glad?

Our Governor recently declared the State of California to be in a "Drought State of Emergency". So yesterday, I gave begarden's becoming-drought-adapted home garden a good soaking. 

Does that sound like a bad thing to do in light of the drought emergency? Actually, no. It is a good thing to do. If you haven't watered your drought-adapted garden lately and you are in Southern California, do it this weekend, and not when weather is warm. Just be sure the air temperature is above 40F when you water. Morning is best. Also, better when air is still.

Yesterday, with lower temperatures, cloud cover, and slightly more humid air, evapotranspiration rate (rate of the combination of evaporation and plant up-take of water) was relatively low. That means, gravity will naturally pull more irrigation water deeply into the soil, because not so much will be "lost" to evaporation. Trees and shrubs will take up what they need, leaving the rest for later and for others. This way, we are also recharging local groundwater, which in part helps support the root system of large, local trees we rely on for summer shade in our hot climate. In general, shrubs and trees will extend their roots more deeply with deep, infrequent irrigation, helping them through periods of drought.

The intent of seasonal, deep and infrequent irrigation is to replicate what nature provides during winter in a theoretically "average" year. Actually, we rarely if ever get an "average" year's rainfall in Southern California. Our average is an average of wetter years and drier years. We tend to have one or the other extreme, sometimes for years at a time. That is why our locally native plants, and secondly, those of similar climates are most well-adapted to this pattern.

If you work on getting your plants well-hydrated and ready for summer now, you can relax in summer while they assume whatever is their drought adaptation response. Some plants, like sages, lose large leaves, retaining smaller leaves. Others, like manzanitas and jojoba, turn leaves with the sun's rays so that little surface area is exposed to the harshest light and heat. (How cool is that?!) In both cases, plants do not die, but rather they slow down their cycle of transpiration and photosynthesis. However, even the most drought adapted plants can die during an extended drought if not sufficiently hydrated. 

The more recently planted is your garden, the more you will need to continue to irrigate. Just be as efficient about it as you possibly can be. Water only within the root zone of plants.

Look first to maintain plants that provide the greatest benefit and in which you have the largest investment of time, money and resources. Generally, those are your established shade trees and fruit trees. Trees grown in a lawn, if you still have one, need to be more deeply watered than they likely have been. Concentrate the most water within a few feet of the drip line of established, large trees. Of course, avoid wetting impenetrable surfaces like concrete or asphalt paving.

Finally, mulch, mulch, mulch… It is nature's way. Keep organic mulch (chipped bark, twigs, leaves, etc.) and any added inorganic mulch (gravel, decomposed granite, etc.) at least 2 feet away from the trunk flare of trees. Mulching conserves moisture, protects soil from compaction, may gradually add nutrients (some of which may be contained in rainfall but generally not in treated irrigation water), and moderates soil temperature. 

For more information on watering established trees, check out this post on Also, follow the blog and Facebook page of

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