Archive for September, 2009

Soil Compaction in Lawns

Saturday, September 26th, 2009

Soil Compaction, Over Seeding and Aeration

After a summer of kids and dogs pounding on the lawn and with temperatures dropping, fall is really the time to aerate and over seed the lawn.

Aeration is a process where holes are punched into the grass and ground allowing better gas exchange, loosening the soil and helping water floe to root zones. Though there are all kinds of gimmicky aeration devices, like the infamous clip on soles with 3” spikes coming out the bottom that you’re supposed to walk on your lawn with, only core aeration really is effective. Core aeration is a process where a cone like device pulls a soil core up and out of the ground as opposed to spiking the ground which has been proven far less effective in aerating root zones and dealing with compaction.

Compaction is a real issue in many lawns and an interesting, a piece in the New York Times on the lawns at Harvard showed that after a couple of years of compost tea applications, many compaction issues were relieved as microbial activity increased and broke down the elements contributing to compaction. A combination of aeration and compost tea are highly recommended for dealing with compaction issues.

While core aerating and turning up all that loose soil, over seeding at the same time will fill in those spaces made by the aerator, and the loose soil form the cores will help the seed to germinate. And sprout. Grass seed germinated and started out in the fall will come in much more strongly in the spring and be far less likely to fail in the heat of the summer than grass seeded in the spring.

If you have a particularly weedy lawn ( more than half your lawn is weeds) thanks to this year’s heavy moisture get rid of the weeds first either by hand removing or spot spraying weeds with a broadleaf herbicide. If the first application does not knock the weeds out, hit them again a week later. Wait at least one week after applying herbicides to aerate and over seed

By the way, herbicides are the antithesis of compost tea, they kill microbes in the soil contributing to compaction which favors weeds over grass. However, if you spot spray the weeds only you will minimize damage to the soil culture and by upping the compost tea, you can restart the microbial activity in these areas.

Fall Pruning and Trimming

Sunday, September 20th, 2009

Fall Pruning

I was “garden coaching” with a couple that are client/friends the other day. The area they wanted help with was fall pruning of trees and shrubs. This was a lovely experience with a terrific couple able to express differences and commonality while having fun together, a real lesson for those of us with overly sensitive egos! He likes to prune heavily while she is more cautious, which may be a Y chromosome issue as I tend to be heavy handed myself. Fortunately, pruning, shearing, and trimming require both qualities.

Distinguishing between what needs what is the first step. Generally, little leaf shrubs like  privet, taxus, and perhaps even forsythia  and burning bush can take a good shearing with a hedge clipper of some sort. Hemlocks would be the exception to that rule (there always seems to be one) requiring careful hand pruning. Larger leaf, slower growing plants like rhododendron, lilac, and hydrangea for example really prefer hand pruning as do almost all ornamental trees.


When shearing in the fall, a good rule of thumb is to remove no more than a quarter of the plant. Maybe a third if the plant has not been cut at all in some time. Remember that cutting a plant stimulates growth, which is OK in the Fall but you don’t want to over-stimulate, as the season is winding down and all plants are storing energy for their winter hibernation. If you want to really go at it, and completely reshape the fast growers, winter or very early spring shearing is advised, preferably before they leaf out much. The early you perform a hard cut, the more new foliage you will get to fill in the inevitable bald spots that will result from a hard cut.


When fall pruning, you are dealing with slower growers and want to be conservative. Feel free to remove deadwood of course, also “suckers” or “water sprouts”. These are little shoots coming out of the main branches inside the tree or shrub. Usually not much light reaches them and they almost use as much energy as they generate sapping the plant of energy it could be expending elsewhere. On trees, look for crossing branches. Crossing branches are branches that are touching and rub against each other when the wind blows, rubbing the bark off of the branch and making it more vulnerable to insects and disease. Remove the smaller branch whenever possible unless you feel the smaller branch is ornamentally more appropriate to the shape of the tree.