Required water for new plants - Knowledgebase Question

Lincoln, CA
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Question by lbrigleb0
August 5, 2005
I have been attempting to develop a better understanding of effective watering techniques for new plantings. In the process, I found the following statement in an answer to a previous FAQ regarding over watered Arborvitae.

?The rule of thumb during the growing season is an inch a week from the sky or the hose. This is most important during the summer months and should be followed for a full year after planting.?

I saw a similar statement in the answer to another FAQ, and have the following questions:

(1) Am I correct in assuming that the 1? requirement means 1? of water for each square foot of canopy cover? For example, a 4 ?? diameter tree would have a canopy cover of about 16 sq ft. Based on the rule of thumb, would this tree then require 16? (or about 10 gallons) of water per week?

(2) If so (and if it were a newly planted tree being irrigated with drip emitters), would the entire 10 gallons need to be applied directly over the original root ball?

(3) The reason for asking Question (2) is that my irrigation system consists of a series of drip lines with in-line emitters. In many cases, I have new plants that do not have an emitter directly over the root ball, and what I am finding is that water from the nearby emitters does not wet the media of the original root ball. Hence, if all of the required water for new plants needs to be applied directly to the root ball, I will need to add some temporary emitters. If I do so (and if I allow the nearby in-line emitters to continue operating), am I likely to over water these plants?

(4) If so, I could temporarily disable the nearby in-line emitters. But if I were to do that, at what point could I disable the temporary emitters and re-enable the nearby in-line emitters. (I am assuming that as plants become established they donot need to have emitters directly over the original root ball. Please confirm.)

Many thanks for your help.

Answer from NGA
August 5, 2005
Determining just how much water to apply can be confusing because the amount of water each plant needs may vary, and different soil types retain more water than others. The important thing is, that the rootmass of each plant should receive sufficient moisture to keep it healthy, One way that you can check to see how efficient your drip system is (or your hand watering practices) is to water as usual and then wait 3-4 days. Dig a hole near the roots of your plant and observe the moisture in the soil. If the soil is moist 3 inches beneath the soil surface, you won't need to water for a few more days; if it is dry, it's time to water again; if it is soggy wet, the soil doesn't drain well and you won't need to water as often. Just how sandy or clayey your soil is (sand=fast drainage; clay=slow drainage), plus the weather, plus the type of plant you're growing. Maybe a practical solution for you with your newly installed plants is to build a watering basin beneath each. Once each week flood the basin with water, allow it to drain, then flood it a second time. Once the roots are established, your drip system should be sufficient.

Best wishes with your landscape!

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