FEATURESTORY
by Eric Hopper
Hardening Off Your Seedlings
W
hen seedlings are started indoors or in
a greenhouse, they become acclimated
to an environment that is much less
severe than the outdoors. It is some-
times hard for novice gardeners to comprehend that
direct sunlight, strong winds, and cooler nighttime
temperatures are simply too much for many seedlings
or small plants to handle. The process of hardening
off is meant to reduce the shock of transitioning from
a sheltered environment to outdoor conditions. The
three biggest factors affecting a plant’s transition from
an indoor environment to an outdoor environment are
direct sunlight, wind and temperature.
Direct Sunlight
Many gardeners do not realize how much more
intense the sun is than an artificial light source. Even
plants grown under high intensity discharge lighting
will have a hard time transitioning into the intensity
of direct sunlight. Tender seedlings and young plants
grown indoors on a window sill or under a grow light
must be gradually transitioned into direct sunlight.
Start by placing the tender seedlings in a shaded area.
After a couple of days in the shade, the seedlings can
be introduced to direct sunlight. Remember, gradual
30
increases are the key to success in the hardening off
process. Each day a grower can increase the amount
of time the seedlings receive direct sunlight. Depend-
ing on the particular plant variety, the grower can usu-
ally increase the duration of time in direct sunlight by
1-2 hours per day. Typically, seedlings should be ac-
climated to the direct sunlight in about a week’s time.
Wind
Many seedlings and young plants get accustomed
to a high humidity environment. When placed out-
doors, the wind and dry air can quickly dry out the
medium and/or the seedlings themselves. If there is a
strong wind present when a gardener is hardening off
his or her plants, it is a good idea to create some sort
of wind block for the seedlings. Cold frames or mini
hoop houses are valuable tools for the hardening off
process and can offer additional wind protection for
transitioning plants.
Temperature
Many gardeners start the hardening off process
when the night temperatures are still too cold for the
seedlings. It may be necessary to bring the seedlings
back inside each evening until the temperature at
www.GardenandGreenhouse.net
April 2018