Hardening off assistance

My last attempt at hardening off ended with the untimely demise of all of my seedlings (except for two). I rushed it, put the seedlings out for the whole day in a full shade area on my back stoop- but then couldn't get home until after dark and the change in temperature pretty much killed the whole lot of them.

I bought one of those collapsible cold frames and was thinking of using it to harden off this time since I'm not home during the day to move them in and out. Have any of you folks used one of these to harden off seedlings? If so, how do you do it with the cold frame?

Any suggestions on successful hardening off would be really appreciated (i.e., a schedule I could follow, perhaps?) because this batch of seedlings looks great and I will be incredibly sad if I inadvertently murder them. :(

Ive never used a cold frame but I usually put mine out in 2-3 hour intervals - in the shade, slowly moving to sun & colder temps - my schedule is something like:
Day 1: Shade 5-8pm
Day 2: Shade 5-8 pm
Day 3: Shade 3-5, part sun 5-7 (sundown)
Day 4: Shade 3-4, part sun 4-7
Day 5: Part sun 3-7, Shade (night time) 7-9
Day 6: Put them out in a sunnier area about 2-3 pm (after the hot mid-day sun) and leave them over night.
Day 7: Same as day 6, but if they are going to be in a full sun area in my yard I usually place them there..
Then they are usually good to go.
I have lost tons of seedlings over the years b/c I would only harden them off for 2-3 days (and usually forget to bring them back in overnight) So the above schedule usually works good for me - of course if you have more tender seedlings you may want to adjust them slower - or vice versa for hardier ones (my tomatoes usually only take 3-4 days.
Good luck!
bre

A cold frame should eliminate the problems that you mentioned. I used one for years (with very little precision, I might add) and do not recall having any major losses (I probably lost some due to watering).

Like you, I work during the day and this was a great remedy for that. There is no 'shade' time here. As long as you have some UV protection in your coldframe top, you'll be fine.

I'm a newbie, so take my advice with a grain of salt.

I used to use a careful schedule, but then I noticed that the seedlings I forgot about over in the corner did just as well as those I took loving care of. The only real no-nos that I've found are: 1) rushing them into the sun; 2) letting them get too cold too quickly; and 3) forgetting that they need weak plant food while still in their tiny pots.

For most seedlings, I switch from keeping them constantly moist to drenching/drying a week or two before taking them outside. This helps prepare them for the real world. I also have a fan that blows gently across the indoor nursery area.

I have a covered patio in back with a metal scrollwork table. I take my flats of seedlings out and put them on the table. They get NO direct sunlight there, but the ambient light is much higher than indoors, and they do get wind. If the temp variation between midday and night is more than 20 degrees, I take the flats back inside overnight. Otherwise, they stay out from day one. I don't worry about ordinary wind, but if there's a storm or other unusually high winds, I take the seedlings inside until the air calms. Otherwise, they stay outside. The scrollwork table lets me water freely without worrying about drainage. I water when the soil is dry, but before it's bone-dry. This usually comes to anywhere from once a day (for very light-soil babies) to every three days (for most seedlings).

After about a week on the table, give or take a couple of days (usually prompted by when I have a new batch of seedlings that needs the table), I move the flats from the table to the ground. For shade plants, I put them just under the edge of the overhang, so they can get very bright light, but no direct rays. The others I put half-way out. The overhang lets the outside ones get sun in the mornings, but shade in the afternoon.

I nudge them outward from time to time. If a flat goes a couple of days without showing signs of stress, it's time to move it further into the sun. If it starts to droop or burn, I move it back toward the shade. (This all sounds far more complicated than it is. I go out in the morning, and shove a few things around with my toe while drinking my first cup of coffee and hoping for rain so I don't have to bend over to pick up the watering can.)

After a flat of seedlings has been in full sun for at least a week with no signs of distress, I pop the youngsters in the ground. The next batch is usually ready to get nudged around in the morning, and the table's full of new stuff.

I follow the same general routine, but speeded up a bit, for houseplants that I want to summer outdoors. A day or two in each position is usually enough. They have good roots, and have been outside before, but just need to be given a chance to remember what wind and sun are like.

By this time of year, only a few rare plants are still inside.