Growing the Desert Garden

Welcome to the Desert Garden, with garden coach Tyler Storey, where we talk about everything having to do with gardening and landscaping in the Desert Southwest. From composting to Cercidium and agaves to arugula — we'll cover everything you want to know to grow your own beautiful Desert Garden.

Wednesday, January 14, 2009

Citrus Month: Spontaneous Lemon Destruction?

I received the following question from a correspondent in Phoenix, Arizona:

We had a very large, lemon-laden branch spontaneously break off our tree. I have attached photos. It looks a little diseased to me. How should we proceed?
Tim
Hi Tim,
The first thing to do is pick and use the fruits from the fallen branch; they're ripe enough and perfectly usable. From the look of the branch in the picture you sent, I think you could get almost a dozen lemon meringue pies out of it. Remember to beat the meringue until just glossy.

Your next immediate concern is to prevent consequent damage to the bark and trunk of the tree, and I'll get to that; first, though, let's take a look at what really happened. While it certainly looks like the branch broke "spontaneously," you might be surprised to learn how long that spontaneity had been in the making.

It's not unusual to see heavily laden lemon branches breaking in Phoenix about now; yet another result of the Great Freeze of 2007. The entire Phoenix area had three days of hard freezes in a row just about two years ago. One of the consequences was that most lemon trees in the area lost varying degrees of new growth, and almost all of them lost their new forming flower buds; the "bud wood." As a result, few gardeners had much in the way of a lemon crop in the Winter of 2007-2008; the fruit had been literally nipped in the bud.

Many citrus, lemon included, have at least a slight tendency towards alternate bearing, meaning they might bear fruit heavily in one year and more lightly the next. Because very few of the Phoenix-area lemon trees had any fruit at all last year, many of them made up for it with extra-heavy crops this year. Those extra-heavy crops have been ripening and gaining in weight over the last several months, and as the weight gets greater, it starts to tell against any structural weakness in the tree. At a certain point: snap!

Broken Lemon ©Tyler StoreyIt looks to me that the structural weakness in your tree was of pretty long standing. I took one of the pictures you sent, enlarged it, and added some arrows so we can look at what happened. You might want to click on the preview picture above for the larger view, so you can follow along.

If you look at the red arrow, it's pointing to a partially broken branch headed off to the left; we can tell by the color of the split wood and the "expansion joint" in the bark that it happened some time ago. That pattern of splintered wood is characteristic of bent and broken citrus limbs.

Now look at the area to which the blue arrow is pointing; it has that same characteristic splintered and weathered wood as at the red arrow. And, just to be certain, notice the yellow arrow; it's pointing to the branch above the new break, and you'll notice that branch is horizontal; it's a larger and older example of the pattern we see at the branch with the red arrow.

And, last, look at the area of fresh wood exposed by the new break; the top portion is U-shaped, with the area at the blue arrow extending down into the U, and the portion that recently broke off was very superficial; in other words, the branch broke off and just peeled the bark and a little wood, rather than splitting the limb in half.

OK, you've been very patient. Now we put it all together:

Some time ago, possibly years ago, the branch that the yellow arrow is pointing to bent over and partially splintered. In response, a bud in the bark, just below the bend, started growing and it grew into an upright and fairly large branch. Because it grew from what we call an "adventitious bud" on the surface of the bark, it wasn't very strongly attached; it's anchor wasn't in the wood, as it were.

This new branch continued to get bigger and branched out and then, because of the heavy crop that resulted from the Great Phoenix Freeze of 2007, it finally got too heavy for its weak attachment and down it came, peeling the bark as it went. What looks like rot in the center is just weathered wood and an accumulation of air-borne dust that gathered in the acute angle between the two branches.

So what do you do now? After you've finished your lemon meringue pie baking, your greatest concern will be preventing sun damage to the bark and trunk, especially if the break is on the West or South side of the tree.

Citrus trees have very thin bark – it's more like skin. When a citrus breaks or is pruned, the previously shaded area of bark is suddenly exposed to the intense Desert sun. The bark "burns" and dies and that causes more problems than the original break, possibly even killing the tree.

Your next step is to shade all of the newly exposed bark, from above the break all the way down to the ground. You can either rig a covering of low-percentage shade cloth, or paint the trunk with a water-based citrus paint.

If you choose paint, I recommend that you buy the "bark-colored" variety. It's a personal opinion, but I think the white paint looks odd, and you will have to repaint in future years to keep it from looking shabby. If you use the tan paint, you need only paint once, and as the tree grows, the new tissue that expands through the paint will be tougher and won't need re-painting. Ideally we don't paint exposed wood, but in this case it's probably best for the tree.

I hope this helps,

Tyler

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