Hardening Off Seedlings
guide to transitioning seedlings from indoor to outdoor conditions
Hardening off seedlings is the process by which you gradually expose seedlings which have been grown indoors, to the outside world. This process is much more of an art than science. I would encourage you to pick a day (s) when you can stay at home and be available to monitor the seedlings throughout the day, and move them if weather conditions change.
The primary consideration during this process is to protect the seedlings from too much direct sun and strong winds. In northern growing areas there is also the challenge of wide temperature fluctuations, and risk of frost at night and snow. This is a rough guide that provides a 5 to 7 day transition period.
Day Before - prepare seedlings by ensuring they are watered in good
Day 1 - put out seedlings when temperature is at least 12’C,(that is usually after 10am for me) in a protected area, which is partially shaded and protected somewhat from the wind. Leave them out for 4 to 6 hours.
Day 2 - Place them in an area where they get full sun for 2 to 4 hours, and indirect sun for rest of time, for a total of 6 to 8 hours. My seedlings get morning shade until 11am. Then they get full sun for 4 hours before I take them in. Monitor the wind and protect them if it gets too strong. A little breeze is good.
Day 3 - water any seedlings that are getting dry and feel light when lifted. Put them out a couple of hours earlier if possible, otherwise keep conditions the same. Leave them out a couple of hours longer in the evening. Total time out may be 12 hours or so.
Day 4 - put them out as soon as you wake up. They may be exposed to full sun all day From hear on in, don’t protect them from mild to moderate breezes, but if the forecast is for strong winds keep them protected somewhat. water any that are drying out
Day 5 - same as day 4. If the forecast is for nighttime temperatures above 5’C, leave them out all night.
Day 6 - same as day 5. Fertilize with a liquid organic fertilizer (I use DirtnGrow organic seedling starter (is derived from digested vegetable meal, rock phosphate, citric acid, potassium hydroxide and kelp meal)
I usually let them dry out for at least one or two days prior to planting. Then the root ball is not too heavy and can be effectively removed from the pot.
