I'm in Northern California zone 10A and I've finally set up my greenhouse! I started my seedlings indoors a couple of weeks back, but I'm eager to move them outside. The nighttime temperatures are still dipping down to the mid-40s until May, and I'm a little worried about transferring my seedlings to the unheated greenhouse. I recorded temperatures inside my greenhouse ranging from 43°F to 105°F. Last night, it only got down to 51°F, so that's a relief, but I'm unsure how much temperature fluctuation my plants can handle. Normally, I would harden off the seedlings daily, but I'm hoping the greenhouse can help me be more efficient. Are these nighttime temperatures safe for them? Also, will the shelter from the wind and rain make a difference? I've got some flowers started (maybe too optimistic?), and some leggy Cosmos that are already struggling under grow lights. I'm ready to get them outside!
4 Answers
They should be fine as long as it doesn’t actually freeze. Just monitor closely and they should do alright!
I personally wouldn't worry too much about nighttime temps in the 40s if you're growing hardy vegetables like carrots, radishes, and peas. Just make sure you have proper ventilation in the greenhouse to deal with the warmth during the day, especially since it can heat up quickly in there. I'm from the South Bay, and while I started all my plants indoors, I've moved them outside and the nighttime chill hasn't been a problem!
Consider getting a heated seed mat if you can run an extension cord out there. It really helps with temperature-sensitive plants like tomatoes and peppers, especially if you cover them with frost cloth at night. But for hardier plants like greens and brassicas, you should be perfectly fine with what you have! Just be cautious of those high temps getting too hot, especially since it's still March!
How is your greenhouse set up? A fan can really help with circulation and temperature control. I have a solar fan planned for mine, plus an automatic window opener to keep things from overheating when it gets too hot outside.