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.

Thursday, March 26, 2009

From the Inbox: Potted lemon

Potted Lemon Tree

From a Correspondent:

I have a potted dwarf Lisbon Lemon that is 3 years old. It finally has bloomed just recently but just doesn't seem joyous. Some of the leaves have a yellowing vein pattern. I imagine it is a deficiency or that I need to repot. Where would you recommend to go for deficiency diagnosis? I want to make my tree as happy as can be! Haven't had much luck with some of the nurseries or blogs.
Thank a bunch,
Isabella
Tempe, Arizona
Good morning Isabella,
Don't spend your time or money on any kind of testing for soil deficiency. Growing citrus in pots in the Desert Garden does take a little extra care, but not that much. As your lemon is three years old and blooming, you've done a good job so far, and only a couple of adjustments are needed if you want it to really thrive.

First, in looking at the picture you sent, it appears that the yellowing leaves are primarily older leaves, from last year or the year before. As with all evergreen plants, the plant as a whole says green year-round, but the individual leaves have a finite life-span. This time of year, it's perfectly normal to see the older leaves on a citrus tree fade, turn yellow, and fall. I'm guessing that's what you're seeing, so there's no cause for concern on that account.

But, let's take a broader look at citrus in pots.

When they grow in the ground, trees have several natural advantages: they have (in theory) unlimited space in which to spread their roots; they have a natural reserve of moisture in the soil; their roots are kept cool by the lower temperatures underground; and the trees can tap into the naturally occurring soil minerals. These are all essential for the tree's health and growth, and they are all missing in a potted tree. Our job, when we grow a tree in a pot, is to keep these lacking elements in mind, and to compensate for them as much as possible.

If you take a look at the picture you sent me, you'll notice that it's a big tree in a little pot; you're right: it's time to re-pot. Your tree needs additional root space to maintain a moisture reserve and cooler roots.

Think about a typical 105° Summer day in the Desert Garden; even if the pot is not in direct Sun, over the course of the day the pot and the soil in it will heat up, just by virtue of the surrounding air temperature. The larger the pot, the slower the soil heating , and the larger the moisture reserve.

You're not going to want to re-pot a lemon tree every few years, so I recommend getting a large pot, some good soil-based potting soil, and re-potting now. Do your tree a favor and get a pot with straight sides. Tapered pots like the one you have now are not very good for trees in the long run; they have a small soil volume compared to their top diameter, and they also have a tendency to tip over once the tree gets larger. Be certain your new pot has a drainage hole and – here's the exciting part – do not use gravel, sand, old potsherds, or anything else to "improve" the drainage at the bottom. Contrary to popular wisdom, gravel in the bottom of a pot will impede drainage, not improve it.

And, last, because your lemon tree will not have much in the way of minerals from its artificial soil, you'll want to fertilize it several times a year with a citrus fertilizer. I recommend using the fertilizer at a rate of about one-quarter the rate recommended on the fertilizer label. Your potted lemon will respond better to several very small and well-spaced doses of fertilizer, rather than one big one, and too much at one time will stress the plant and possibly damage it. Whenever we fertilize, either in a pot or in the ground, always water first, then scratch in the fertilizer, then water again; this should prevent the fertilizer from "burning" the roots. These light fertilizer applications will take care of any mineral deficiencies that are showing up in the leaves.

I hope this helps,
Tyler

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