Planting Annuals When the Nights Are Still Going Down in the 40s

Hardening-Off Transplants

• Spring and summer annuals can usually tolerate lower nighttime temperatures, but you must take the time to help them adjust to outdoor conditions. Hardening-off the transplants in a protected area, such as near the house or under a patio overhang, for a few days helps them adjust while still allowing you to protect them from late season frost. Set the plants outside for a few hours the first day, and then gradually increase the time over a week so they stay out all day and night by the end of the hardening period. Continue to water the plants when needed as they harden-off, and bring them indoors if there is frost.

Successful Planting

• Annuals that establish healthy roots quickly are less prone to damage from brief periods of cold. Prepare the soil in the new garden bed before you plant by mixing in 1 or 2 inches of compost and any fertilizers needed by the specific plant variety. Plant the annuals on an overcast day or in the afternoon so they aren't stressed by intense sunlight right away. Transplant nursery and potted plants at the same depth they were growing in their container, following the spacing recommendations for the plant variety. Water immediately after transplanting so the soil settles around the roots. Water with a starter fertilizer solution, such as 1 tablespoon of a 24-8-16 blend diluted in 1 gallon of water, to further help the plants establish quickly.

Mulching Method

• Mulch further minimizes the effects of cool nights, especially for annuals that thrive in warmer soil. Cover the bed with 2 inches of bark or wood chip mulch to help insulate the soil against temperature fluctuations. You can also use black plastic sheeting to help absorb and retain heat during the day. Camouflage the plastic with a thin layer of wood mulch. When applying mulch around new transplants, pull it back so it doesn't rest against the tender stems.

Frost Protection

• When nights are cool the occasional frost may still occur, which is more damaging to newly planted annuals than temperatures in the 40s. Fortunately, these frost are usually short-lived, so you can protect your annuals. Exposed plants are in the most danger, but covering them with cardboard boxes, upturned cans or plastic sheeting provides sufficient protection for most summer annuals. Arrange the covering so it doesn't touch the plant's leaves or stems and remove the covering promptly after the frost passes, otherwise the plants may overheat.