I am growing lupin seedlings under lights. When can they be planted out in South East Etobicoke? Can they tolerate light frost like pansies?
In recent years, the last frost date in Toronto has been determined to be around May 9. This is an average of 1981-2010 temperatures calculated by Environment Canada. There may be variations depending on topography and local weather. It’s a safe bet to plant your seedlings around the Victoria Day weekend. But even if there were to be a light freeze, it would be unlikely to kill your lupines. Definitely do not plant them out in April, especially with the unpredictable weather we are experiencing this spring.
A word of caution when transplanting lupines. They do not like their roots to be disturbed. When picking out individual seedlings choose the strongest looking ones and include a good clump of soil around the roots. Plant them in an individual pot at least 2 1/2 in. across filled with a sterile potting mix. To save disturbing the root again use fibre, peat or biodegradable pots that can be placed directly into the soil when transplanting into the garden. Make sure you plant the seedling quickly in a hole that has been thoroughly soaked.
All seedlings coming from an indoor environment must gradually become acclimatized to the outdoor environment. Therefore, it is a good idea to “harden off” young seedlings for a week or so before planting them outside in the garden. Hardening off means keeping them mainly in the shade and only gradually giving them full sun to prepare them for their spot in your garden. Put them outdoors in a sheltered area for an hour the first day. Each day, for the next several days, increase the length of time and the exposure to the sun. The plants will then be ready to be transplanted into the garden. A cold frame is extremely useful for this purpose.
Your plants will be happier if they’re planted when the weather is cool and the ground is moist. You don’t want the roots to dry out, so the ideal time is when the sky is overcast. If it’s a very sunny day, plant in early morning or evening when the location is in the shade.
Lupines love full sun and average to moist soil. These plants can be fussy but they certainly make a good display in the summer garden. If you are lucky they will self seed and come back another year.
For further reading see links below:
https://www.torontomastergardeners.ca/askagardener/starting-seeds-too-early/