Hardening Off Seedlings

Late May News: Hardening off Seedlings Before Transplanting

Flint prepares flats of onions for their move outdoors.

Flint prepares flats of onions for their move outdoors.

Garden seedlings can be put into two basic categories: seedlings that are tender, and seedlings that are hardy. Tender plants will not tolerate temperatures below 32℉ (i.e. they will die), while hardy seedlings can experience frosts and freezing temperatures and survive. There is a range in each category, some plants being very tender like basil, and some very hardy like onions. For specifics about the hardiness of your seedlings, check out Johnny’s Seeds Grower’s Library. They some wonderful tips on hardening off specific types of vegetables, herbs, fruits and flowers.

At Cate Farm, we start everything from seed here in our greenhouses, in East Montpelier. Once plants have been potted up, some remain in a greenhouse before being sold, while others are grown outdoors on benches to harden them off. The plants that remain in a greenhouse benefit from a gradual transition to the outside growing environment before transplanting to your garden.

Cate Farm greenhouses have roll up side walls, so seedlings experience some wind even though they are not outside. That being said, the greenhouse plastic diffuses and reduces the impact of direct sunlight, provides plants with extra heat during sunny days and protects them from cooler nighttime temperatures. To get your greenhouse plants ready for transplanting, we recommend that you incrementally expose them to direct sunlight for a few hours a day. A little wind is good too, but not too much. Move the plants from direct sun to your porch, or bring inside if below 40℉. After a few days of this treatment, your plants will be ready to put in your garden.