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Wednesday, April 25, 2012

Relying on Lawn Water to Water Trees and Shrubs a Waste of Water


Q. I have a patch of grass in my back yard and I would like to put plants, shrubs and flowers around the perimeter. Can you tell me what type of plants to put since they will be getting their water from the sprinklers?  I follow the watering schedule for my area and during the summer months there will be a lot of water so I would need to know what plants and shrubs like a lot of water.

A. This is not how we should be thinking of watering in the desert. Plants that grow on the perimeter of a lawn survive because of the over irrigation of the lawn. If we give the lawn precisely the amount of water which it needs, there will be very little water left for plants growing along the perimeter of it.
This Siberian elm has died back because it was surrounded
by grass and now was replaced with desert landscape
and rock mulch
            Lawns should be irrigated so that the water supplied to them is adequate and no more. Plants growing along the perimeter of a lawn should be watered so that they get precisely enough water as well. This would require that these perimeter plants be irrigated with their own irrigation system, not with water coming from the lawn.

            Lawns are watered frequently and with small volumes of water because of their shallow root system. Other shallow rooted plants, like annual flowers and vegetables, are watered in the same manner and require the same frequency of irrigation.
            Deeply rooted trees and shrubs are watered less often but with a higher volume of water so that their entire root system is wetted when the irrigation has been completed.

2 comments:

  1. I hear what you are saying, as there is an assumption that it is OK to add much water. Seems the lawn should be not only efficiently irrigated so there is little "overspray", but allowed to live but perhaps go dormant some until fall?

    Though in all practicality, if the irrigation oversprays, it is not being applied more than is necessary, isn't it OK to take advantage of the overspray that exists?

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  2. extremehort@aol.comMay 3, 2012 at 10:08 AM

    The problem is the lack of uniformity of the irrigation system. This is the part where waste occurs. You are right. Only enough water is added from overspray but the question then becomes how evenly is the overspray applied? Since overspray has poor uniformity then where overspray is just enough it is fine but overspray that is too much due to poor uniformity is wasted.

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