I have more seedlings than I have room under my lights, so I put mine out if it's above 15 degrees out. They've been going out for part of the day for over a week now because of the nice weather. This weather is unusually warm though, normally it's still too cool, so it is on the early side to be hardening off seedlings.

If you're able to keep a close eye on both the seedlings and the weather, it won't harm them to go out as long as you start them off in the shady and sheltered location. But don't put away your indoor set-up just yet - the weather is bound to drop back to normal sometime soon.

BP

Hi adair and BP, I've started to harden off my plants this week and because it's unusually warm I am able to leave my trays of plants outdoor in a covered porch all day long. I have been bringing them in at night though. I expect I shall start extending their time outside sometime next week but I do have to watch for sudden cold spells which could mean disaster for annual seedlings.

This weather is just so unusually warm that I got myself confused as to whether I could begin planting out now. But just to be on the cautious side, I am approaching this carefully. Also it's worth checking the online 14 day forecast online.

Ianna

Thanks BP and Hi Ianna, I know it is early but the weather being so warm it makes you want to get out there. I was only putting some out for awhile during the day,it is starnge I almost feel like they are my "kids" and can't be left out too long. Lol. Happy Gardening !!

These seedlings are babies of a sort - I've been known to cry when the squirrels or some other nasty event destroys them :-)

I know in my area, the average last frost day is May 3rd, and that's usually about when I harden off most of my seedlings and I'll even plant a few of the more hardy ones. This year all bets are off!

BP

Oh, I'm a mean mom. I sent mine out last week and haven't seen them since! I did the occasional check up and watered them - they are doing really well. No damping off and no mildew in the soil. My main concern is something eating them but so far so good.

I could leave them out at night too ? What temperature would be too cold for them? The low here tonight is 6

adair, no not yet. Take it slow. Or if you wish to erect a cold frame, then it's possible. Without any cover, they will likely get killed off.

Ianna

Definitely still too cold for the night for most seedlings in my zone 5a.

Tomatoes, eggplants and peppers ideally should not be exposed to anything lower than 10C - it'll slow them up big time (I will leave mine out once the *average* night temps are 8C and up (another two weeks away at least) - but they're next to a brick wall that was in the sun all day and that keeps them warm and happy. Other veggies like onions, spinach and kales will be ok as long as it's several degrees above freezing. Some herbs can take 5C and not suffer (chives, thyme, savory, oregano), but others need slightly warmer temps (basil, rosemary). Most perennial seedlings will be ok at 5C and up, but many annuals will prefer to have 10C and up. Pretty well any tropical seedling will need 10C and up.

There's also a difference between the temperature a seedling can survive and the temperature it thrives at. If they get too cold, their growth will slow or even stop if they get too cold. Better to drag them in and out for a couple of weeks longer and have bigger plants for it.

With this warm April we're having it's very tempting to leave the babies out, but it's too risky to leave them out for the night. It's not just the temps you have to worry about - a heavy rain or strong wind can kill them off too.

BP

Thanks for all the help here I have learned so much in such a short time from this site. Still learning lots with all your help.

Had my seedlings outside last weekend. Started with a couple hours of gentle morning sun. A few days later they were pretty accustomed to about 4 hours. How easy they adapt to outdoor light depends alot on the type of plant and how much light they were getting indoors. If they were grown under plant lights, they seem to adapt to outdoors easier. If they were just on a bright windowsill, they may leaf scorch so use caution. I always say if the leaves get some scorch so be it, the new leaves outdoors will be nice and healthy, but too much leaf scorch may kill the plant.

I left the plants outdoors one night, but they were in a mini-tiered greenhouse and I threw a blanket on it. Still, I find that this time of year they may forecast +4 for an overnight low (which, in theory, it would stay slightly warmer in the greenhouse), but in reality it hit about 1C.

Anyways, my plants will have to start from zero in adapting to outdoors once again since it's a mini version of winter today, +1 with snow/rain/freezing rain. Ugh!

It was great to get yard work done on the weekend, however, I had a few shrubs to move and the cool weather following is actually great for them. Plus, wanted to move them while still dormant. For anyone that grows holly, I was worried about moving it but they really don't get that extensive of a root system after 4 years, do they?

Glen

Oops. Thanks for the info. Maybe if I wasn't so lazy, I'd have better gardens - sigh. Have to start researching more!