You know it's autumn when the leaves change color... but why do they?
It's so dry, I'll quote a local tree grower I ran into years back. When I asked him how dry it was in his field, he said "It's so dry out there, the trees are followin' the dogs around."
Not sure exactly what that means, but I think that means it's pretty dry.
Once you hit the season when trees are changing color, dropping a few leaves, and generally pulling on their galoshes for the winter, it can be hard to know what to do about dry soil. We all know trees need water. We all know that good, deep, and regular watering is key to long-term tree health. We also know getting water down deep to tree roots can be a challenge. Do they need the water right now since they're headed into dormancy?
Here's what to know on how to water your trees this fall.
Good question. And there are lots of ways to measure drought. We can look at rain statistics, but that only tells us how much rain fell over the last few months. It doesn't tell us how much of that rain soaked into the soil. It also doesn't tell us the impact of things like cloud cover and air relative humidity over the last few months. Suffice it to say that on our giant new Castle Gardens construction project at Yew Dell Botanical Gardens, the crew digging holes for the wall footers are down three to four feet deep and finding nothing but dust.
Good question, considering that most trees are seen as more or less shutting down for the winter. The thing is, trees really need water in the fall.
In spring, when tree buds pop open and start putting out new shoots and leaf growth, there's a tremendous need for plenty of water. In fact, in trees like oaks and buckeyes that have most of their new growth cells pre-formed in the winter bud, it is the roots pumping water up to the new growth that is the driving force behind that burst of spring growth. All those preformed cells inflate with water that the roots pull out of the soil and pump upward. But water is key in the fall, as well.
Fall forms what tree physiologists call the second wave of growth. No, the trees aren't putting out new shoot and leaf growth in fall. But they are putting on lots of stem/trunk growth. The fall is when trees put on the majority of their trunk diameter growth. Spring growth is such a nutrient sink that it absorbs just about everything available. The trunk waits its turn and does its thing in the fall. Without adequate available water, trunk growth is reduced, and you end up with a weak or poorly supported tree.
This is one of those things about trees that I have always found amazing. It's easy to understand, at least conceptually, how a tree pulls water from a spring soil. There's plenty of moisture sitting around. Sometimes you can just dig a shallow hole and it almost spontaneously fills with water. But what about when it is bone dry out there? The answer is a cool bit of anatomy and physiology.
If you think of a tree as a giant straw that sucks water out of the soil, you miss a big part of what makes trees tick. The straw analogy will work to get water up about 20 or 30 feet. But once a tree gets taller than that, the tension on all those water molecules isn't strong enough to hold it together. The water column will cavitate and fall apart. Trees break up the steps of pulling the water from vessel to vessel so each step is smaller than the whole. The result is not just the successful transport of water up an 80-foot-tall tree trunk. It also exacts tremendous force to bring water into the roots from very dry soil. It may not look like there's much water down there but if there's even a tiny bit holding on in the soil, trees will get their hands on it.
Yes!
Once the soil gets very dry in fall, it will indeed take a whole lot of rain/irrigation to get the water down a foot or two or three into the soil. If you go out there now and turn on your sprinkler and let it run for four hours, best case scenario the water will have penetrated maybe an inch into the soil. And that's assuming that none of the irrigation water has run across the dry yard, into the street, and down the storm drain. At this point, once it starts raining (and it will - I assure you!) it will likely take a few months to rehydrate the full 2- to 3- feet of root zone soil. But that doesn't mean you should pass on watering in a dry fall.
If you have to prioritize watering, go for the newly planted trees. They don't have the extensive root systems of a mature tree and most need the extra help. But whether you are watering the old trees or the new ones, the key is regular watering - not letting the soil you managed to rehydrate, dry out between waterings.
And if that doesn't work, look around for a few golden retrievers.