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It's OK to get snippy with those little oaks

Q. In the autumn of 2006, we had a bumper crop of acorns in the front yard that proceeded to sprout. I have several hundred seedlings that are hard to pull, so I've been cutting them. Will they eventually give up? Is there a better way to remove them?

A. Oak seedlings are not as difficult as mulberry, elm or maple seedlings to remove, but you must get rid of them within two years of germination. Oaks grow a deep and thick root before they put on much top growth. The root may reach two feet down and an inch in diameter in two years. The fledgling trees typically grow no more than 12 inches tall and have fewer than a dozen leaves, offering little hint of the massive root system below. In the first year or two, they are still fairly easy to pull up if the soil is saturated, because they don't form that many lateral roots until their third year.

As you suspect, repeated removal of the top growth will beat them back. By snipping the top, the roots will run out of food eventually. If you take this approach, be dutiful. Sprouts will appear where you cut, and these must be cut off before the new leaves are fully expanded.

Two consecutive years of defoliation are usually enough to kill any oak seedling.

Q. We have many shrubs around the house that spread by runners, namely oakleaf hydrangea, nandina, fothergilla and clethra. I have tried to cut back the suckers but this method is time-consuming and getting harder each year. Could I use Roundup or another spray that would kill the suckers without harming the parent plant? If not, what would you suggest?

A. Instead of fighting the natural tendencies of these shrubs, work with them. Like most shrubs, yours produce new branches from the base to replace old ones that are no longer vigorous. If you use Roundup on the sprouts, it can seep into all parts of the plant, resulting in injury or death.

Of the shrubs you mention, only the nandina truly has rhizomes that can sprout a significant distance from the parent shrub. You may want to consider replacing your nandina with something else. The dwarf forms of nandina are much less likely to produce these rhizomes.

The other shrubs don't have rhizomes, but do grow vigorous shoots near the base of the shrub. Instead of focusing your efforts on removing that new growth, concentrate on removing some of the oldest branches. Cut a few of them to the ground every three to five years. The younger shoots will fill in, and you will be rewarded with healthier foliage and larger masses of flowers on the more vigorous branches.