Everyday Gardener: Plants trees now and be sure to water them

Everyone talks about spring being the best time to plant trees and that is true, usually. But fall is also a great time for tree planting as long as you don’t choose birch, firs, oaks and most fruit trees. Those do best when they get a spring start for reasons that are not really understood, though some think it has something to do with tree’s root systems. Trees with a large taproot that grows deep into the soil — rather than a network of finer roots closer to the surface — should not be planted in the fall, they say.

I’ll just add that my own completely unscientific research confirms that birch do better when planted in the spring. I have three birch trees, well, two now. The survivors were planted in the spring and the dead one was planted in the fall. It kicked the bucket in less than two years, which is when I Googled to find out what was up and discovered that I probably sentenced the poor thing to an early death by snapping it up at a fall plant sale and putting it in the ground.

Ah, sales. As you probably know, a lot of garden centers drastically slash prices in the fall. So if you’ve been thinking about planting a tree or two but have held off due to sticker shock, now is the time to buy. You’ll often get deals on delivery too. One thing to be aware of before buying trees in the fall, however, is that they do need a little extra care to help get established before winter.

Fall-planted trees need a little extra love

One of the biggest reasons spring is thought of as the best time for planting trees, shrubs and other things is the fact that is usually rains quite a bit. New trees need to be kept well watered, particularly for the first two years, so they can establish a strong, deep root system to help them stave off pests, disease and drought. If it doesn’t rain at least an inch per week, you’ll need to water your new trees yourself. If you don’t think you’ll follow through with watering, don’t plant a tree in the fall because it’s very likely it won’t survive the winter if its young root system is already stressed when the ground freezes.

Research suggests that young trees with trunks that are around 2-inches in diameter generally need about 1 inch or 5 to 7 gallons of water each week. I say “generally” because trees planted in sandy soil may need additional water while trees in moisture-holding clay soil might need less, for example. When you water, concentrate on the new tree’s root ball, so picture the size of the pot the tree came out of as you water and you’ll be good to go. Short, frequent watering isn’t good because it doesn’t foster deep root growth. That’s why it’s best to water just once or twice a week, depending on how quickly your soil dries out.

Figuring out how much to water is tricky because the best way to water trees is with a drip system or hose turned on very low. (If you use a hose you’ll need to move it around the base of the tree as you water so it gets all sides of the root ball.) So how do you know when you’ve got 5 to 7 gallons? Excellent question — and it is not easy to answer because, honestly, now that I think about it, I’ve just been trotting out this gallon amount for years just like University Extension websites do. In the future, if you’re ever at a talk I’m giving and I offer some amorphous, unhelpful advice like this, let me know so I can get a grip, please.

Like a lot of people who’ve gardened for years, I just kind of guess/know how much to water. So I asked other master gardeners for help coming up with some reasonable ideas for measuring when watering young trees. They agreed that this is a tricky question. Here are some thoughts:

1. Forego the hose and use a sprinkler on low at the base of a tree (so you’re not wetting the leaves). That way you use an inexpensive rain gauge, pie tin or other container to figure out when you’ve watered an inch. After one hour, just outside the root ball area, dig down about 5 to 8 inches with a trowel. If it’s wet, you’re fine. If not, you need more water. Try another half hour and check another spot.

2. Use a soaker, drip system or hose and water the root ball for an hour. Use a trowel to check the soil.

3. Put your hose on very low and let it run into a 5-gallon bucket to see how long it takes to fill it. Once you know, you can use your hose on that same setting to water for the same amount of time. Use a trowel to check soil moisture.

4. Poke or drill holes near the bottom of a 5-gallon bucket. Fill it with water and move it around the base of the tree a couple of times as the water drains out. Again, use a trowel to check soil moisture just beyond the root ball.

Help young trees retain moisture by mulching around the base of them. Mulch also helps limit weed growth and serves as a good reminder to keep lawnmowers and weed whips away from the trunk. Spread mulch in a circle to about 3 to 4 inches deep. Mulch should look like a flat circle, not a volcano. For more information on important things such as how deeply to plant trees, read this handy Extension publication: extension.umn.edu/distribution/horticulture/dg3825.html.

Meleah Maynard is a writer and Master Gardener. Her Everyday Gardener column appears monthly in the Southwest Journal.