From a Correspondent:
I live in Oro Valley, Arizona, near Tangerine and La Canada (this info in case there may be a unique 'micro' climate here). My husband and I are thinking of planting about 7 desert trees in the back part of our property. We're thinking Desert Museum Palo Verde and Mesquite — I am not sure which variety (any suggestions there?). When I phoned the nursery, the man who answered told me he had a 'special' going on because he was overstocked – and that NOW ('monsoon season') was the very best time to plant them. He went on to say that the rains would help establish the trees, which makes sense on one level to me, but I thought the very hot summer temps would stress the trees too much. He said no. I'm thinking that the investment of 7 boxed trees plus delivery and planting represents a big investment and I would like to get your input.
Thanks so much for your time.
Oro Valley, Arizona
Good morning Tessa,
I am always leery of overstock end-of-season "specials." Except for donuts; I'm a sucker for day-old chocolate-covered donuts. But boxed trees are — as you point out — a much bigger investment than are stale donuts.
So let's dissect this. First, you're right to be interested in micro-climates in your area. You're definitely in the Desert, but you're also right down-slope from a little "island" of snowy-winter mountain, and the entire area is corrugated with roughly North-South arroyos. In your area, your micro-climate is going to depend on where you are in relation to the arroyo, and on the contours of your property. For the most part, though, it will be more of a cold-season issue.
So on to the trees. Palo Verde and Mesquite are both excellent choices. I am not a big fan of hybrid Palo Verdes such as the "Desert Museum," but it's not a bad choice. For the mesquite, I strongly recommend sticking with the natives, rather than the foreign varieties. The Honey Mesquite, Velvet Mesquite, and Screwbean Mesquite are all excellent choices and hardy in your area. Each has a different form and habit, so look them up to see which fits your plans.
Autumn or Spring is the preferred time for planting trees, especially large boxed trees. You're right about the heat stress. A boxed tree does not have the root system in place to draw the water necessary to support itself once it's in the ground. That's one of the reasons I always recommend buying small trees — 15-gallon or 24-inch box at the largest. Smaller trees of those sizes have roots more in proportion to their canopy size, they undergo less stress in planting, they will establish faster and will catch up with and surpass the bigger boxed trees.
Also consider that a box is a tough place for a tree to grow under the best of circumstances. Now, as the Spring planting season has ended, those "special" trees will have been in the box for a long time. It's more likely that their roots have suffered from heat scald, or that the roots have started to circle the container. Circling roots are always bad — despite our best efforts, they will never "un-circle."
Trees are a long-term investment and their success in the future — even years into the future — depends on planting them under the best possible circumstances.
I would recommend that you wait to plant your trees in the fall. Fall planting means that the trees will put on good root growth in the still-warm soils while suffering less heat stress in the cooling air temperature.
If you have to plant big boxed ones, go to the nursery and select the trees yourself. Find ones with adequate levels of soil in the box, with no circling roots, with a canopy that is not too over-big for the root-ball size, with sturdy trunks, and that have as many lower branches as possible. And try to buy ones that haven't been sitting in a hot box all Summer long. When you plant them, don't prune off any lower branches for at least a year, and don't stake the trees unless it is absolutely necessary. Do be certain to remove the nursery stake that's right up next to the trunk.
Even better, buy 15-gallon trees, dig the holes and plant the trees yourself, and save a bundle of money. You'll have healthier and faster-growing trees, and you can use the savings to buy some nice desert-adapted plants to place under your new trees. And possibly a few donuts.
I hope this helps,