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How to Cultivate a Hydrangea Cutting and Protect Surface Roots

By Scott Aker
Special to The Washington Post
Thursday, March 19, 2009

Q I took a cutting from a neighbor's hydrangea in the fall. It still appears to be alive, in a pot rigged with a plastic tent over it. What now?

A Keep it in a cool room with indirect light, and keep it just barely moist. Every week or two, gently tug on the cutting. If it resists movement, the roots have begun to form. If that's the case, cut back on watering and remove the plastic. As the weather warms in spring, you can either plant it in the garden or grow it in a pot until it is larger. Don't fertilize it until it has begun to grow. Keep the plant out of direct light, but give it as much indirect light as you can. Next winter, keep it in a protected corner of your garden or mulch it heavily, but after that it should be well established and able to fend for itself.

I have six 100-year-old white pine trees with a lot of surface roots. I have been driving over these roots for more than 35 years with no apparent damage. This year we purchased a tractor with a snowblower, and it is scraping the bark off the roots. I am sure this is not good. What, if anything, can I do? Can I seal the exposed part of the roots with a product?

Like wounds on branches, wounds on tree roots will eventually heal. Treating the wounds with any kind of sealant will, if anything, prevent healing and promote decay. Driving over the area for more than three decades has added to your woes. The inevitable compaction of the soil has forced the roots to grow at the surface. This may not be a problem if the feeder roots beyond the drip line extend into looser soil. But be sure to confine any traffic to the area that is already compacted.

You can avoid future injury from the snow removal equipment by taking a few measures. In the compacted area of the root zone, lay coarse gravel between the exposed roots. Add a layer of finer gravel on top of this to bring the grade up to a level that is just a bit higher than the roots. The gravel will protect the roots, and they still will have air spaces that allow oxygen to reach the roots.

I normally don't advise placing gravel in a tree's root zone because it can cause compaction, but your soil is already hard-packed. Keep gravel off areas that have not been compacted by vehicles.

Scott Aker is a horticulturist at the U.S. National Arboretum.

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