I have successfully germinated 4 white spruce seedlings. I placed the damp seeds in the fridge to stratify them and then placed the seeds in a seed tray, and they are currently growing under grow lights with a heat mat under the seed tray. Should I take them off of the heat mat and remove them from under the grow light? Also, can I pot them up in spring and place them outside (after hardening off)? Thank you!
Thank you for contacting Toronto Master Gardeners. White spruce (Picea glauca) is a native tree to Ontario and is one of the most important species for forestry in the province. There are 29 species of White spruce, 3 of which are native to Ontario. These spruce grow well in a wide variety of soils, moisture levels and light conditions.
First let me offer some general information. There are several ways to germinate White spruce. Stratification can occur naturally outdoors over the winter when seeds are planted outdoors in fall. Stratifying indoors can be done by placing seeds on a damp papter towel in the refrigerator for 21 – 45 days or the the seed can be moistened with sterile peat in a covered container and placed in the refrigerator. Finally, cold stratification can also take place in the freezer by placing the seed mixed with peat in a covered container and freezing solid for 2 months. The stratified seeds should germinate indoors in pots in about 30 days.
You note that your seeds have already germinated and produced seedlings so there is no need to continue to use the heat mat. You do not need your grow lights if you have a warm, sunny place to put the seedlings while they are indoors. It is most important to keep the roots from drying out – moist, but not left soaking in water. Check them regularly and inspect for mold. Once the seedlings are 8 or 9 centimetres tall they can be transplanted to a bigger pot with additional soil to ensure the plants stay moist.
After the last frost (average last frost date in Toronto – May 4/24), the seedlings can be moved outdoors to a sheltered location for hardening off gradually exposing them to light. When you are ready to plant, dig holes about three times the diameter and the same depth as the containers that the seedlings have been growing in. After planting, add soil from what was dug, then spread organic mulch around the saplings. Mulch should be about 5 to 8 cm deep and extend outward 60 cm. Ensure that the mulch does not touch the seedlings’ trunks and keep them consistently moist throughout the first growing season. Small White spruce seedlings are sensitive to frost damage and should be planted where they have some wind protection.
You may also be interested in the following Garden Guide:
Planting a Tree for Life: A Toronto Master Gardeners Guide
and this website of the Ontario government:
https://www.ontario.ca/page/white-spruce