Newcomers to the desert regions find it strange, even illogical, when old-timers recommend planting trees in the fall, when winter is so close.
Here’s the rationale. In the conventional planting time of spring the soil is cool and the air temperatures are quickly getting higher day by day because the sun is getting stronger. The new leaves quickly lose moisture but the roots aren’t gathering it from the cold soil, so a newly-planted tree dries out and dies.
Switch over to the present time, the months of September and October. The days are shortening, the sun is lower and losing it’s fierceness, air temperatures are falling but the soil temperatures remain high. If you apply moisture to this set of conditions you have a perfect opportunity to plant a tree. Soil temperature at seventy degrees will remain for a few weeks.
Tree establishment relies on new root growth and this happens in warm soil. Meanwhile cooler air temperatures slow down the tree’s inclination to put out new leaf growth, even hastening leaf fall of deciduous trees.
Recently I was asked by a troubled gardener to give him the names of some trees that he could replace his dying Desert Willow with. It was dying because the soil stayed wet for a long time after an irrigation. I told him that the problem was that the soil was probably not prepared well enough and it was not a tree problem. But he didn’t like to hear this.
Anyway, tree planting calls for adequate soil preparation and this means digging a planting hole that disturbs a tightly packed desert soil deep enough to allow easy root growth. Three feet at least and if there is caliche at less than five feet that needs to be removed to provide good drainage. If water doesn’t soak into the soil the roots won’t grow downward. Providing good drainage is critical to good tree planting. It doesn’t hurt to add organic matter and nutrients (such as ammonium phosphate) to the backfill either.
At the nursery, pick a tree with a good taper to the trunk, thicker at the base than at the top. If there are shoots and branches lower down the trunk, leave them there, don’t tidy them off because they provide nutrients directly to the lower part of the trunk that increase taper. Trim them after a few months of usefulness.
Stomp the soil as you fill back the hole and finish a little higher for tree planting. The soil of the hole will invariably sink and you don’t want the tree to sink with it.
Stake the new tree lightly, to allow the trunk to flex during a light breeze, but be held when the breeze becomes a gust
Water often and widely to get new roots started but cut back when you get the first frost. Keep the soil moist, but not wet, all winter.
Don’t get impatient about new growth in the spring and remember that it usually takes a complete year before your tree is established and is no longer a nursery tree out of the nursery.