From now until May, all bets are off!
I have already posted most of this in the September gardening guide on nhgardensolutions.com, but in case any of you missed it:
Though you may hear that it’s anywhere from the 11th to the 21st, tomorrow, September 15th is the traditional first frost date for this area and weathermen are calling for nighttime temps in the 30s by the end of this week. Though usually light and scattered at this time of the month, frost should be expected from now on. On average, in Keene, NH on September 15th the chance of frost is about 50%. By September 27th it is closer to 90%.
Gardeners should watch forecasts carefully and be prepared to cover their tender vegetables like tomatoes, annuals, and other tender plants with tarps, sheets, or even newspaper at short notice. Hardy crops like those in the cabbage family, any root crops, most perennials, and garden mums will be fine uncovered.
If you are overwhelmed by green tomatoes and don’t want to cover them, pull the plants up by the roots, (or dig them) knock off all loose soil, tie some stout twine around the base of the stem and hang them upside down in a shed, garage or basement. Any bits of soil remaining on the roots will help keep them moist. Most of the tomatoes will still ripen in spite of such harsh treatment. This should be done before a frost kills the foliage, and they should be in a place where temps won’t fall below 32 degrees F after they are hung.
Over the previous two weeks house plants should have been slowly acclimated to growing indoors once again by being brought in over night. If not they should be brought in now or at least put undercover on a porch or in a garage. Tropical houseplants will suffer any time the nighttime temperatures fall much below 55 degrees F and even a light frost can finish them off, so they shouldn’t be outside at night. Leaving the windows open during the day after they are brought in will also help them adjust.
Those wishing to do more planting or transplanting of spring bulbs, perennials, shrubs and trees shouldn’t despair because there is still plenty of time for new plantings to establish good root systems before the soil freezes solid in December. It may seem like we’ve had a lot of rain lately, but new plantings should still be watered deeply at least once each week and more often if it hasn’t rained. Plants can lose a lot of moisture in winter and soil moisture amounts can be very deceiving at this time of year, so they should be monitored to make sure that soil is good and moist when it finally freezes. Don’t rush to put those hoses away!
I found the photo of frost rimmed leaves on a website that offered free nature screen savers .