GARDENING: Critical time for controlling weeds

By Jeff Floyd

Certified horticulturist and arborist

Seeds don’t remember things, at least not in the sense we can. If they could, they’d probably like to forget Stevie Wonder’s 1979 album ‘The Secret Life of Plants.’ In it, the singer put artistic license to the test by attributing humanlike thoughts and emotions to plants, threatening to derail his musical winning streak in the process.  However, the artist was not entirely off-base. Seeds do develop a memory of sorts; a physiological record, if you will, which helps determine when they’ll sprout. We can use this information to stop weeds before they become a problem in the landscape.

The amount of time a seed occupies the soil at a given temperature is a defining factor in the timing of its germination. Let’s say a tiny crabgrass seed is hiding out in the front yard. It has good contact with the soil and takes up water and oxygen easily. We know from previous years that around Valentine’s Day, soil temperatures hover near 50 degrees Fahrenheit for a few hours each day but may drop back into the high 40s overnight.

Our imaginary seed’s growth chemicals were activated at 50 degrees and the sprouting process began. When the temperature dips below 50 at night, the process stops. As soil temps rise above 50 again the next day, development continues where it left off. The higher the temperature climbs above the threshold level of 50, the faster the rate of development. After a few cycles like this, our seed will send down a delicate root followed quickly by an upward sprout. This is a critical time for controlling weeds.

Crabgrasses and dandelions begin to sprout when soil temperatures remain between 50 and 55 degrees for several days. In fact, many common lawn weeds sprout in this temperature range and hug the soil surface for weeks as small seedlings. They are difficult to see at this stage of development.

Feb. 14 is an ideal time to apply a pre-emergent weed control to kill young weeds before they develop into unsightly problems. Labor Day is also a great time to apply pre-emergent herbicides. Pre-emergents work by killing the rapidly dividing cells of developing weeds but weeds won’t remember that. All they’ll remember is to stay out of your yard.