Irrigation Wells

I have heard that it would be good for my Coast Live Oak (Quercus agrifolia) to provide some wells for giving it Summer water. Some oaks, such as Q. englemannii, are fine with a dry Summer, but agrfolia seems to prefer a little more moisture during the warm, dry months. The problem seems to be that giving it surface irrigation during warm weather may foster soil pathogens that agrifolia is particularly susceptible to. I have heard of some oaks being killed by surface irrigation in the Summer months. Q. agrifolia in the wild handles this by locating themselves where there is subterranean water, such as adjacent to a seasonal stream. In the garden we have to come up with other methods.

One answer is to create a well at least 2 ft. deep in order to get down below the level where the soil is warmed in the Summer and below where most of the pathogens live. I was told about a method for doing this, and I decided that Winter is the best time for installing these, when the soil is damp and the tree is not under stress. I began by selecting the locations for the wells. I wanted them to be within the drip line of the tree but not too close to the trunk.

Next I bought an auger bit for my drill.

It produces a 3" diameter hole. Notice that it has a very long shaft, 28". Without this long shaft it wouldn't be possible to get down deep enough. I looked for one of these at the local Home Depot but they didn't have it. I had to order it online to get the long shaft version. It was about $30 including shipping.

Drilling the hole can be a bit tricky. There are likely to be roots and rocks in the soil, so work around these with care. One must also be careful if your drill is powerful. At the very least it can wrench the whole thing out of your hands. In a worst case it could injure you. As you are digging, pull the bit up to the surface frequently to bring the dirt up and out of the hole.

When the whole is finished, the next item needed is 3" PVC sewer pipe. This is available everywhere. I cut it into 30" lengths so that a few inches would stick up above the hole. I also bought caps to cover the ends of the pipe so that I can keep it covered. I don't want it filling with dirt or leaves because that would eventually defeat the purpose of having a well. The pipe was about $15 and the caps were about $1.79 each.

The caps are normally a tight fit, so I sanded the top end of the pipe where the cap will sit in order to make a looser fit. Then I spray painted the cap and the top end of the pipe with a matte green color to camouflage it.

If you've done it right, the pipe should go down into the hole with just a bit of pushing. I finished this off by putting a few inches of gravel in the bottom of each pipe. With the caps on, the pipes are hardly noticeable.

I won't be using these until the rainy season is over. Then I will go to an irrigation schedule of roughly every two weeks. If I have water left in my rain barrels, I'll use that. When that's gone, I'll just put the hose into the well and let in run at a very low rate for an hour or so in each well. It will be interesting to see if there is any observable difference in the tree, such as less leaf browning this coming Summer, or more vigorous growth the following Spring, or more acorn production.