We know that trees make Claremont a beautiful and pleasant place to be; provide food and shelter for wildlife; create shade that reduces evaporation from the soil, lowers the surrounding air temperature, and reduces energy costs; filter pollutants from the air and from water absorbed by the roots; and not inconsiderably add to property values.
All good reasons to make a new year’s resolution to help us remain a City of Trees! We can do that by pruning and watering them properly (and luckily, that isn’t hard!).
So, about pruning:
- Why prune? This can be done to promote fruit or flower production, but for ornamental trees the goal is to keep the tree healthy and safe, with a natural shape. Sometimes a lower branch or two might be removed or the foliage thinned a bit to let more light into a bed below. If a tree is being pruned to keep its size down, it may be better to replace it with one that won’t outgrow the spot (full disclosure, though: I inherited an old Eugenia that I like that gets pruned to reduce its size every four or five years, but I make sure it never looks like anything has been done).
- How often do trees need to be pruned? Many fruit trees require annual pruning but those grown for beauty or shade generally require much less. As trees mature, the need for pruning often decreases, especially if they have been chosen with regard to their eventual size and shape. My cedar has been pruned once in 35 years, and that just to get a few branches off the roof, and my 25 year old crape myrtle has never been pruned.
- When should they be pruned? For most trees, this should take place in the fall or winter when growth is slow and when birds aren’t nesting. Dead, diseased, or dangerous wood can be removed pretty much any time.
- How much should be pruned? The current thinking is that no more than 25% of the canopy should be removed at any time, and often less is better. No tree should ever be topped –throw away cards from anyone advertising that! Keep an eye on your tree trimmers and don’t be afraid to tell them to stop--bottom line: If it’s obvious a tree was pruned, it wasn’t a good job!
- What happens if too much is pruned out or large stumps are left? The aboveground and belowground parts of a tree normally grow in tandem. If there is a sudden decrease in photosynthesis, some trees such as elms may go into a decline and actually die from the shock. In other species, the loss may trigger growth from dormant buds to replace the lost leaves, producing unsightly masses of vertical “water shoots” along the branch or ugly tufts (“witch’s fingers”) at the cut ends.
- Doesn’t heavy pruning reduce future costs? Nope. Often so much growth is stimulated that more pruning is necessary the following year. Not only does this rampant regrowth obscure the natural shape and beauty of the tree, suckers are often more prone to breakage because they are more weakly attached to the main branches than the original branches were, and this can result in costly safety issues.
And now to watering:
- How often do trees need water? Newly planted trees need water weekly for the first year, but mature trees only need it once or twice a month depending on the season and the species. If your tree starts looking pale, or the leaves droop or start turning brown, or if branches are starting to die, reassess your watering schedule!
- Where should the water go? The water needs to cover an area starting from about a foot away from the trunk and extend at least to the edge of the canopy. And it needs to soak into the soil to a depth of about two feet, where most of the water-absorbing roots are located.
- Can I just use water bags? Water bags are only good for helping young trees to become established. The water spreads down more than outward so they only water a limited area. The best thing for larger trees is drip irrigation or a soaker hose spiraled around in the whole area out to the edge of the canopy.
- Should I mulch the area under the tree? Mulch does help the soil retain moisture and prevents evaporation when you are using your soaker hose, but it should be kept about a foot from the trunk to prevent the base of the tree from staying wet and rotting. Although groundcover plants use up some water, they can also act as a living mulch and provide their own benefits. Gravel can work too but may absorb too much heat.
- What if I’ve converted to more waterwise planting? Trees still have all the benefits listed above, so you don’t want to lose them. If you replace lawns or other parts of your garden with drought-tolerant plantings or hardscape, you’ll need to be sure that the tree still gets enough water. You may be able to wean the tree from frequent, shallow waterings to less frequent, deeper ones, but that needs to be done slowly over the course of a year or more to allow the tree time to adapt.
- Isn’t watering expensive? Happily for those of us watching our pennies, each time we water an average tree the cost is much less than for a cup of coffee, and the benefits the tree provides are worth much more than that!
So, for 2020, let’s resolve to prune our trees sensibly, and to water them carefully! If we do, this will make a great contribution to the benefits we receive from our personal gardens and to the beauty of our City of Trees!
Demystifying Sustainability articles are a joint effort of Sustainable Claremont (www.sustainableclaremont.org) and the Garden Club (www.claremontgardenclub.org).