HG: Homegrown Column December 06, 2008
We read your little blurb about the purple ash tree in the paper.
We recently planted 14 of these trees along our driveway. They are 14 feet with 4-inch trunks. Our concern is that we have very high alkaline soil.
We brought in some good soil and mulch but would like your opinion and/or suggestion as to what we can do to help ensure the survival of our trees.
We were told they were one of the better trees for this kind of soil, is that true? Any and all info you can give us would be greatly appreciated.
Ash is a fine, durable tree for this area. It will tolerate alkaline soil fine and its moderately salt tolerant, but it does have its limits.
Understand that there’s a difference between soil alkali and soil-soluble salts. People often confuse the two, but they are different issues.
Alkaline soil is simply a soil that has an alkaline pH. Though an alkaline soil can sometimes have issues with certain nutrient deficiencies, it’s rarely an impediment to growing most things in western Colorado unless you’re trying to grow acid demanding plants such as rhododendrons or blueberries.
And though soil salts are somewhat alkaline in nature, changing the pH of the soil really won’t help with a soluble salt problem.
If you’re really concerned about this, get a salt test run on the soil.
Take a hand trowel, and dig up a good scoop of the soil.
You want a vertical slice of the soil. Don’t just scrape off some of the surface soil.
Since the soil’s makeup can vary from place to place, it’s helpful to take several scoops, mix them up in a bucket, then take a cup or two of that soil in to get analyzed. This way, you get a more “average” sampling of your soil.
You mentioned that you added some good soil. I wouldn’t take soil samples from this area. Take soil samples of the existing soil you have in the area.
The reason is that if you do have salty native soil, those salts will migrate into the good soil you’ve added, making it as salty as the native soil, eventually.
The Colorado State University Extension office in Grand Junction can give you a salt reading. It takes only a few minutes, and they don’t charge for the service.
Knowing the salt levels is important in determining whether there is a problem and deciding what to do (if anything) about it.
Generally, we like to see a salt reading below 4 millimohs (mmoh). If it’s higher than that, it can be problematic in growing some plants.
For an ash tree, I’d probably be comfortable with a salt reading below 5 or 6.
If you find that the soil is too salty, the only solution is to leach those salts down deep into the soil, below the roots of your plants. Basically, you just water the area and continue watering until the salt levels have subsided.
One thing that helps facilitate this is amending the soil by mixing in a good amount of low salt organic matter into the soil. Make sure that the material is low in salt; most manures are pretty salty.
This amending will help open up our naturally heavy clay soils and help them drain better, which makes leaching those salts down easier.
This heavy irrigation and soil amendment are all fine and good but it’s pretty difficult to accomplish when plants are growing in that area.
What I’d concentrate on is watering your trees deeply and thoroughly when you do water, then let the soil dry out just a bit before soaking them again.
This will lower salt levels; it just takes longer to achieve.
I’m not trying to frighten you. The likelihood is that your soil is fine, but I want you to know what you’re up against and what to do if you find you have a problem.
I was wondering if it is OK to cut branches from my smoke tree this time of year, or would it be better to wait until March? Thank you so much for your answers. You’re the best.
Honestly, it probably doesn’t matter a whole lot whether you prune in the fall or the spring.
The problem with pruning in the fall is that you’ve created some open wounds, and the tissue can desiccate in our dry climate over the winter, occasionally causing some additional die-back.
That doesn’t happen very often, so you’d probably never notice the difference.
It’s better to wait than to prune in the fall. You want to be absolutely sure that the plant is completely dormant and won’t be stimulated to push out new growth in response to the pruning. Wait until the end of November or the first part of December.
I usually do my pruning in March because the plant is about to wake up and begin growing so it can start healing the pruning wounds.
It’s also a nice time to prune because after a long, cold winter that’s when I’m at my most enthusiastic about getting out in the yard.
It’s better to prune in early spring, but the differences between spring and fall are pretty small.