Herbs, houseplants and seedings benefit from added light

Herbs growing on windowsills, as well as smaller houseplants, can benefit from spending a few months under artificial lights to supplement diminished natural sunlight. Homeowners can construct a light table using two 40-watt, full spectrum, fluorescent lights, one cool and one warm, for each foot of shelf space filled with plants. Try to group plants with similar heights together so the light fixture can be set as close to the plants as possible - a few inches above the plants is best. Keep the lights on for 14 to 16 hours a day.

• Plants growing near windows and getting sunlight primarily from one direction benefit from an occasional turning as their growth tends to turn toward the light. Routinely rotating the pots promotes growth that is straight.

• This a good time to cut buckthorn out of native and garden areas. When the ground is frozen, there is minimal to no damage to desirable plants from the removal process. There is less impact on herbaceous native plants when this work is done on frozen ground.

Be sure to treat stumps with an herbicide such as glyphosate or triclopyr to kill the root system. Glyphosate needs to be used at a high enough concentration to work as a stump treatment. Some recommend a 50% concentration, but Chicago Botanic Garden staff has had success with a lower concentration of around 30%.

One of the drawbacks with glyphosate is that it is water based, so it freezes at low temperatures and is only effective on the cut surface. Triclopyr is the preferred method during subfreezing weather because it is oil based, effective through the bark and on the cut surface, and will not freeze.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.