Emma Erler, host of Homegrown NH and lead horticulturist with Kirkwood Gardens, has some tips for extending the life of potted herbs from the grocery store.
Over-watering is the number one reason most herbs don’t last long, says Erler. Plants suffer when potting soil remains saturated for extended periods, indicated by yellow leaves that drop, or the entire plant wilting.
Erler says the plastic sleeve the pots come in should be removed, since they keep the soil waterlogged. It’s time to water only when the soil is dry to the touch. Allow water to drain away from the bottom of pots and never leave them in standing water for long.
Herbs require a fair amount of humidity in order to thrive, something most NH homes lack in the winter. The most effective method to create a more humid environment is with a humidifier located near the plant. A less effective method is to fill a pan or dish with moist pebbles and place the container on top, making sure that the bottom of the pot is not submerged in water.
Most herbs need a minimum of 6 hours of direct sun a day. An unobstructed south facing window may work. Otherwise, a grow light running 14-16 hrs a day is critical.
Thin and spindly stems are signs they aren’t getting enough light. Basil, parsley, cilantro, chives, and oregano require high amounts of direct light, while bay, rosemary, and mint can handle indirect light.
Most herbs need warmth in order to grow, and need to be in a room that is 65-75 degrees Farenheit during the day, and 55-60 degrees at night. Herbs may survive at lower temperatures, but they won’t grow. Temperatures lower than 50 degrees for an extended period will kill basil.
Supermarket herbs are often planted too densely. A small pot that is only large enough to support one healthy herb may be packed with a dozen or more. Though this may give the pot a nice full look when purchased, this is not a recipe for long-term success.
If you hope to keep your herbs growing throughout the winter, you’ll either need to thin the plants or divide and transplant them into separate containers. Thinning the plants can become a part of harvesting.
When you thin the plants, avoid disturbing the roots of the seedling you are keeping by snipping the other stems at the base with scissors.
Once you’re down to a couple of individual plants, harvest herbs only when they reach a height of six inches, and remove no more than a third of the plant at a time.
If you are able to tend the herbs through the winter, they’ll be much happier planted outside.
See you in the garden!
Homegrown New Hampshire is a collaboration between Squam Lakes Natural Science Center and NHPR.
