Good Trees/Bad Trees (or) The Problem with Poplars

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Question. What is your opinion of hybrid poplars? I've read that they grow very fast, can provide firewood in four to five years, and that if you cut the tree and leave the stump in the ground, it will grow another tree that will provide more firewood in another four to five years. Thanks.

--- Steve in Beavercreek, Ohio

Answer. The technique of cutting and recutting the same tree for firewood is an essential element of the "Alley Cropping" system that the late Bob Rodale championed as a way to help combat soil erosion in the Third World. Plant trees that regrow after cutting, he explained, and there would always be working roots in the ground to hold soil in place and manage storm water. The growing trees would also function as windbreaks; and if you choose members of the legume family, their nitrogen-rich leaves and branches can be used as an excellent plant feeding mulch or compost ingredient.

(For lots more details on Bob's excellent ideas on fighting world hunger, pick up a copy of "Save Three Lives" (Sierra Club Books; 1991). I had the honor to work with Bob on this wonderful book, which is sadly out of print—but used copies are readily available on the Internet. Check it out; you'll enjoy it.)

But while the basic idea of Alley Cropping is sound, the choice of tree here is not. All poplars produce a fairly soft wood that is far from ideal for heating. You can tell just by splitting it that it's more like paper than a true hardwood. (I have an 'emergency' wood stove and lots of poplars on my property, but learned early on that the wood is just no good.)

And hybrid poplars have the added non-distinction of being named "One of the Eleven Trees You Should Never Plant" in a list that was just released by the National Association of Realtors. Bred to be cheap and fast growing, these brittle trees are incredibly short lived. (Here's a link to the complete list of losers.)

Instead, I'm going to suggest one of Bob Rodale's favorite Alley Cropping trees for growers in the US—the black locust. It grows quickly, regrows from stumps, and sends up suckers that grow into full sized trees. Its hard, dense, wood is prized for home heating, and its natural rot-resistance also makes it a great choice for wooden structures that come into ground contact, like compost bins, raised bed frames, fence posts and trellises. Because it's a legume, the leaves and small branches are rich in plant-feeding Nitrogen, and it blooms brilliantly in the Spring, producing flower clusters that smell like orange blossoms. (Honeybees love the flowers, and the honey they produce after visiting a black locust in bloom is prized for its rich flavor.)

A little Internet hopping also suggests that the hornbeam would be another excellent choice as a regenerative firewood tree. It's very attractive, regrows from cut stumps and produces a hard, strong wood that's said to burn especially slow and hot.

Just be aware that these are not trees for close quarters; any tree that regrows from a stump and/or sends up shoots and suckers can become an invasive problem. But if well sited and well managed, a tree like the black locust can provide wood for fires and structures, excellent erosion and wind control and food for plants and bees. Not too shabby.

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Question. A good buddy of mine has decided to remove a cottonwood tree that invades the pipes around his home so aggressively that he has to have them cleaned two or three times a year, despite the trunk of the tree being a good 40 feet away from the pipes! But he really likes the shade it provides during our short but hot summers, and wants to get a replacement. I suggested a conifer, because I never heard of one attacking pipes. But he wants a deciduous tree. Any suggestions on deciduous trees that won't attack pipes or foundations?

---Dustin in Spokane, WA

Answer. Sure—but they won't grow nearly as fast as that cottonwood (another member of the often notorious Poplar family). Nothing comes without a price, and the 'price' for a well-behaved tree is often a slow to medium rate of growth. Conversely, it's a good general rule that the faster a tree grows, the more aggressive the root system and/or the weaker and shorter-lived the tree. A lot of homeowners latch onto the promise of 'instant shade' and wind up paying massive bills for sewer line cleaning and tree removal because they didn't realize that the words 'fast growing' actually mean 'big trouble'. If you want shade faster, start with a bigger, older tree. Sure, it'll cost more up front, but it could save you thousands in the long run.

The worst pipe-attackers are willows, sweet gum, poplars, many of the maples and some of the oaks. I combined recommendations on well-behaved trees from the Washington, DC-based non-profit group Casey Trees with a list of drought-resistant varieties for your unusual Spokane climate from the Washington State Extension service, and came up with redbud and fringe tree as your top choices. If the tree can be watered in the summer, add Japanese maple and dogwood to the list.

But before you accept a short list from someone on the other side of the continent, I urge your friend—and every homeowner—to contact their county extension office before they choose a tree; they have the local knowledge and experience that can help you select the perfect tree.

Oh—and tell your friend to see if that piping needs repair before the new tree goes in. When tree roots clog a pipe, it's often because the pipe was leaking water and attracting the roots, not because the bad tree attacked the pipe.

And if there were roots inside the pipe, the pipe is obviously no longer sound.

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