City Trees

mountain laurels all have lustrous dark green leaves and other signs of vigor, your soil is probably acidic to some degree. But if they are consistently showing pale yellow leaves, your soil is likely alkaline. Sample Scenarios This is a matching game. What are the site opportunities and restraints? Scenario A • You live in USDA Hardiness Zone 5b. • This part of your yard is flooded in the spring, but then gets quite dry in late summer. Ergo, you need something that can tol- erate extremes of soil hydrology. • There are no overhead wires or under- ground utilities in the vicinity. There is plenty of above- and below-ground space. • Your soil is acidic to neutral (under 7.5). • You like big trees, but you hate raking leaves. A good match. You have lots of room, so why not go for something that gets really tall (60 feet or more)? The guide shows that the majestic bald- cypress (Taxodium distichum) is adapted to both seasonally wet and dry soils. It is hardy to Zone 5a or higher. The leaflets are tiny and need no raking. Scenario B or, Not Every Site Can Support a Tree Your soil is impenetrably hard to dig in and/or bedrock is close to the surface. You could remediate a discrete area of poor soil with compost and deep tillage, but it will be expensive to create enough hospitable soil volume for tree roots, which grow well beyond the canopy. There is one site problem that we cannot select for—and that is lack of rooting space. Best not to plant a tree here. Or say you've always wanted a weeping cherry but there is only 10 feet clearance between house and sidewalk (weeping cherry trees get much bigger than that over time). Or, you want an oak tree, but there are overhead wires in the vicinity. Find a place in your landscape where these trees will have adequate above- and below-ground room, look for compact cultivars, or consider a dif- ferent tree so it can enjoy the longevity you wish for it. Excerpt from Part 3: Roots Grow Like Plates, Not Mirrors. How to Protect Them. Most of us grew up with—and still often see—illustra- tions of a tree's root system depicted as a mirror image of the tree's canopy. However tall and wide the canopy, that's how deep and wide the roots grow, right? Turns out, that's not the case. For the vast majority of species, tree roots grow close to the surface and spread laterally in a webbed plate; the roots get finer in width the farther out you go. You may have observed this yourself on trees that are growing on, say, the edge of a river bank, where some portion of their root system is exposed. Have you ever been digging in the garden, nowhere near a tree, and found fine tree roots and been at a loss as to where they came from? Fine "feeder" roots Fine "feeder" roots not only grow horizontally beyond the dripline, there is often a higher percentage of them beyond the dripline than within it. 34 CityTREES

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