IMO you are ok to start hardening off. I try to keep them out of the wind as much as possible. Just do it gradually and you should be fine.

They only need a few days of hardening. 2, 4, 6 hours, then out. But only when the soil temps are 50F at 4" deep.

I would harden the plants for about 2 weeks. A few days is not nearly enough based on my experience. Start in the shade for only about 15 minutes then work your way up to a full day/night. Trying to rush the hardening always results in sun/wind burn in the garden. Temps should be OK for the short periods they will be outside at first.

You could start but I would wait, and I would not leave them out at night at this point. It's a gradual process. I think temps in the 40's at night is iffy. I'm in zone 5b with a similar plant out date, and I wouldn't do it. This has been a tricky spring!
JMO!
Sharon

I would agree that you are rushing the process and should wait at least 1 more week to see what the weather is and does first. Normal planting for most of us will be delayed this year so you may find May 24th to still be too early in your zone.

I'd love to start the hardening process just to get them some real sun.,

There is a risky assumption in that statement. Young seedlings that have been growing indoors don't want or need or even tolerate "real sun". Nor is it the purpose of hardening off. Shade is the most they can handle at first anyway while getting used to the wind, UV rays, and air temps. So pushing the process can quickly send all your efforts to date down the tubes.

Dave

This post was edited by digdirt on Sat, May 3, 14 at 15:10

I never started hardening off seedlings until the weather was such that they wouldn't have to be taken back in, except when there were heavy rains or high winds.

Then in full shade for a couple of days, partial shade for a few more days, then full sun for a few more days, but never less than a week and usually more.

THey need time to toughen up the leaf cuticle and if that doesn't happen then once set out they can be sunburned and or wind burned or both. Those damaged leaves should be allowed to fall off normally, not manually taken off, and new folaige will appear. But why even put the plants at risk if it can be avoided.

When temps are as cold as you mention, so is the soil, and so the transplanted seedlings will just sit there and sulk and not grow.

IMO much better to not only take a long time to harden off, but also to be sure the soil has warmed up.

Carolyn

As Edweather said, go ahead with the hardening off process.

Once they are hardened off , lows in low 40s are fine.
Believe me I have just done it with many nights with lows around 39F and my plants now are growing, budding and flowering.

Just go and visit you local Home Depot and Lowes ! Are they selling tomato plants ? Do they leave their plants unprotected at the nights , outside? And remember that plants in the ground stay much warmer than in 4" pot.

On the other hand if you are expecting a WONDERFUL weather in a week, maybe it is worthwhile to wait. But for me (Planted out early April ) such WONDERFUL weather would have been 7 weeks down the road.

I think it is to early. I am in Toronto and I am waiting another 2 weeks at least. Better safe then sorry. There is not one day in the next two week forecast that it is going to be above 15 degrees here max.

I would listen to Dave and Carolyn. As mentioned planting is going to be later this year. I was advised June 1st. It's not worth the risk and you absolutely cannot expose them to full sun in the beginning. And you are in a zone that the weather can turn in a heart beat, not that it can't in any zone but for those of us further north, it's always trickier.

It really depends how low 40 and how protected your spot. I have no issues taking plants out and leaving in protected spot with mid to high 40 at night. For example I would do near south wall of your house lets say, specially if it has protected nooks. 40th with high wind and bad rain is different from nice cool weather with sunny day. Just my opnion. I do keep an option of draggin entire trays in the house if needed. Depends how many seedlings you have and what are you planning to achieve by this early hardening.
You can also rig some deep box with a lid as a make shift cold frame.

Thanks all,

I'm not planning on planting out until later in the month when temps are higher. I mostly want to get them outside to get some growth on them before I plant them out. My lights are working fine but I always find they grow better once outside. It's not a huge deal to move them out as I use 3" star plug trays.

I usually do the hardening off process over four or five days and have never had any issues. I also run the fan on them every day so I'm not as concerned with windburn.

It has been a weird spring here but the garden is drying out, the garlic is almost 8" high, for some reason I have a huge patch of self-seeded sorrel and all the various chicory, lettuce and arugula seeds have sprouted. Interestingly a large patch of Italian parsley also managed to over-winter and is doing great. So it'll be interesting to see how the season goes for tomatoes. Last year was horrible here.

I'm in no rush to get them into the ground but would like them to start getting some sun.