I grew some kale seedlings in my kitchen on the countertop. They are very spindly. They do not appear to be sturdy enough to survive the night outdoors nor rain. I have been putting them in a sunny spot during the day, and back in the garage at night. How can I thicken the stems or toughen them up?
You're right--if plants don't have enough light, they will really s-t-r-e-t-c-h to find it and in the process, get spindly. Putting them out in the sun each day will help.
If you are past freezing, go ahead and put them out if they are big enough. You can put Wall 'o Waters around them to protect them, or you can cut the bottom off gallon milk jugs and put those over the plants for a few weeks.
Check out these photos.
I love kale and color so what better plant than Red Russian Kale! When planning a garden don't restrict yourself to plants available locally. Consider the options of starting plants from seed.
This is a page about growing ornamental kale. Keep your fall garden colorful by adding ornamental kale to your other late blooming annuals and perennials.
This is a page about growing brassicas. The plants in this genus are members of the mustard family and include, cabbage, broccoli, kale, Brussels sprouts, and cauliflower.