North Country home horticulture: Can't see the lawn for the forest
By PAUL HETZLER
My lawn is a vast Lilliputian forest of two-inch tall trees, a carpet of closed-canopy maple seedlings punctuated by dandelions. It's hard to tell, but a few blades of grass may have survived. Anyone with large maple trees in their yard probably has a lawn in similar condition. So what happened?
It all comes down to stress. Not the stress you feel trying to figure out what to do with 10,000 tree seedlings per acre (a fair estimation, by the way), but rather stress the trees felt when they ran out of water in 2012. That summer saw the driest soil conditions on record in northern NY, and trees really felt it. Dr. George Hudler from Cornell's Plant Pathology Department says that in a summer like 2012, trees suffer extensive root death, and that it takes them two to three years of good conditions to recover from that stress.And stress, as everyone knows, causes helicopters. In 2013, most trees produced what's known as a distress crop, creating many times the normal amount of seeds. Apparently this is some kind of evolutionary response, a bid to perpetuate the species in the face of potentially lethal conditions. Sugar maples and red (soft) maples alike, along with their much-maligned cousins the boxelders, cranked out “helicopter” seeds at a rate that would make Sikorsky, Airbus and Bell envious.
The purpose of maple helicopters, of course, is to fly. The winged seeds, technically known as samaras, did just that, insinuating themselves into every flower pot and sidewalk crack, not to mention onto many lawns. And there they've sprouted quite nicely, saving their species from extinction in superlative fashion but creating trouble for gardens and lawns. That's what happened—now what can one do about it?
Since we've never before seen this heavy of a seed crop, it's unclear how great an impact the baby forests may have on lawns. In my case it seems they're shading out the grass in some spots, but when I cut at the recommended three-inch mower setting, most of the seedlings were unscathed.
Although a three-inch setting is optimal for lawn health, it may be advisable to break the rule for one or two early cuttings to remove the maple “umbrella” and let the grasses get ahead. Once the trees have been weakened by close mowing, switch back to the higher setting to allow the grasses to shade out the forest. This is the best strategy general weed control, but since maples are more shade-tolerant than most weeds, it's unclear how effectively they'll be suppressed.
If you apply a broadleaf herbicide to your lawn every year, do not increase the rate. A broadleaf weed-control product containing 2,4-D will kill maple seedlings the same as any other weed.
For those who want a less toxic option, there is a new active ingredient on the market called Iron HEDTA, a water-soluble form of iron that kills most broadleaf weeds. Because it's fairly new, it may be hard to find, but the more inquiries there are at major garden centers, the more likely it is to be carried in the future. As with all pesticides, read and follow the label carefully.
If my mowing strategy doesn't control the maple patch that used to be my lawn, I'm going to call the DEC and ask if there's a forest-management plan for producing toothpicks. I'll let you know how that works out.
Paul Hetzler is a forester and Cornell Cooperative Extension of St. Lawrence County horticulture and natural resources educator.