Is it too early to transplant tomatoes and cucumbers to the hoop tunnel? What is the earliest day this can be done?
Dear Gardener, thank you for asking your question about when to put out your cucumbers and tomatoes in your hoop tunnel.
With today’s (April 8th) glorious day-time weather of 17 degrees with a nighttime temperature of only 11 degrees, it is very tempting to put out your heat-loving vegetable seedlings in the garden. The protection of a hoop tunnel (also known as a cloche, row-cover, or plant cover) is very effective in protecting plants from being killed by the frost. They are used to extend the growing season by allowing gardeners to have plants start growing outside earlier and to extending the harvest later.
You specifically asked about putting out your cucumbers and tomatoes. Most tomatoes and cucumbers are warm season plants and should only be planted after the danger of frost has passed. Under normal circumstances that is about May 24th in Toronto. The hoop tunnel will allow you to put out your seedlings much earlier – maybe as early as the end of April or the first week of May. That being said, you need to be very careful to harden off the seedlings (more below), and bring them inside if the temperature is going to drop below 13 C degrees.
The growing temp for tomato seedlings should be maintained at a constant temperature of between 14-16 C. Tomato temperature tolerance for cold snaps is of extreme importance to the development of blossoms and subsequent fruit set. Blossom drop will occur in the spring if daytime temperatures are warm but night temperatures drop to below 13 C. Cucumbers (that originally came from India) are even more temperature sensitive and cannot tolerate night-time temperatures fall below 18 C.
I have just looked at the 14-day weather prediction, and they are expecting the temperatures to start dropping next week. They are predicting night-time temperatures to drop below zero degrees by April 20th.
Finally, hardening your seedlings is an important issue. Keep in mind that the process should be slowly done over nearly a two-week period, increasing the time that the plants are outside gradually, and making sure that you bring them in at night if the temperature is predicted to drop below 13 degrees. When you first bring your plants into the sunlight, they should be put in a shady spot for a few days. They should also be protected from any strong winds as this can also cause the leaves to scorch. Your hoop tunnel can be very useful for that purpose. Ensure that your plants are well watered. Avoid any fertilizer for the first week or two outside.
A very helpful resource that might help you is a recent Toronto Master Gardener response to general questions about growing under hoop tunnels. https://www.torontomastergardeners.ca/askagardener/hoop-tunnels/
There is also a Toronto Master Gardener Gardening Guide that you will find interesting: https://www.torontomastergardeners.ca/gardeningguides/extending-the-season-with-cold-frames-a-toronto-master-gardeners-guide/
April 11, 2021