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Transitioning seedlings to outside

Posted by megbun 5b MA (My Page) on
Thu, Apr 11, 13 at 10:26

Hi everyone,

I've been making a lot of use of these forums and the search feature, but I haven't found exactly what I'm looking for. I appreciate any help!

I have a tray of mixed seedlings in cell packs (kale, lettuce, collards, chard, marigolds) that I started about two weeks ago and for the most part are looking quite good--all have at least 1 set of true leaves. They've been set up in a South facing window with supplementary light (2 clamps with 26w 6500k CFLs, 1 desk lamp with a 2700k 23w CFL). When the temperature is decent, I've been opening the window and giving them as much unfiltered sunlight as possible. I also have a fan on low circulating air in the area.

Because I have limited space, my hope is to start hardening them off a bit early, so I can start a few more seedlings in the next week or two. I'm not anxious to plant them in the ground (especially the marigolds), but my hope is to get the seedlings to the point where they can finish growing outside or on my porch to save some space.

1. Can I harden them off, and once they are hardened, move them inside to our screened in porch at night to give them frost protection or will that negate the hardening off process?
2. What sort of daytime air temperatures should I be looking at before I put these relatively young seedlings outside for hardening off? Other than tomorrow, the 10 day forecast has all our daytime temps in the 50s or above.
3. What sort of nighttime temps should I aim for to keep them on the porch 100% of the time? Nighttime temps are less friendly in the forecast--upper 30s mostly.
4. For future seedlings, would starting them outside in cell packs, but moving them inside at night for protection make them "pre-hardened", as it were?

Thank you everyone for any help! This site has been a great resource for me (very much a beginner)

Follow-Up Postings:

RE: Transitioning seedlings to outside

A couple of questions jump out at me. First, if I recall correctly your zone plant out date isn't until mid-to late May, correct? If so then you started them too early and it is far too early and the weather too risky to be hardening off this early. It is normally done 7-10 days before plant out date. So when do you plan to plant?

Second, you say these are only 2 weeks old and have only 1 set of true leaves, correct? If so then they are awfully young and small to tolerate the stresses associated with hardening off.

Granted they are all cole crops except for the marigolds and are cold tolerant but all that means is that cold won't kill them right away. It doesn't mean they will tolerate it for long nor will they benefit from it in any way.

The temp range used by commercial growers for all the plants you list is a maximum low of 45, nothing lower than that. Any thing less might be tolerated for brief periods but should be avoided whenever possible. And of course older plants will tolerate it better than young seedlings.

Hope this helps.


RE: Transitioning seedlings to outside

Average last frost date for my zip is May 10, which puts me 4 weeks before as of tomorrow. I don't plan on putting in the warm weather plants until probably a couple of weeks after that, however, depending on the weather forecasts.

I used this site for seed starting dates:

According to that, the kale, collards, and chard should be able to be transplanted now (if they were full size), lettuce a couple of weeks from now, and the marigolds obviously not for a while (though they said start seeds 6-8 weeks before frost, which is what I did). It's possible that site is wrong though, in which case my dates are obviously a bit off :)

In an ideal world, the chard, kale, and collards would go in ASAP, but I realize they are still babies. I was honestly hoping that I could get them finish growing outside for the last couple of weeks in the sun, since everything I've been reading indicates how much better it is for light.

My main concern though is creating some space indoors on my one sunny light-supplemented windowsill, since there are a few other things I'd like to get started. The marigolds will also have to stay there for quite a while.

Ideally, I'd like to have the tolerant seedlings outside during the day and then bring them into the screened in porch at night. The daytime temperatures around here are relatively friendly this time of year, but the nights are not so much. Being a complete newbie, I'm not sure if that ever makes sense though, so I appreciate the input.

RE: Transitioning seedlings to outside

  • Posted by gjcore 5 South Aurora Co. (My Page) on
    Thu, Apr 11, 13 at 14:41

Maybe you can setup some sort of a coldframe on the porch area to speed things up. Not sure how many plants you have. A laundry basket turned upside down covered with row cover and or painter's plastic as a cheapo example. . Or you can make inexpensive coldframes out of rolled fencing, painter's plastic and rocks or bricks and just have that out in the yard. Gallon containers filled with hot water can release heat most of the evening. Some people recommend painting them black when I've used them before I filled them with various food dyes.

This post was edited by gjcore on Thu, Apr 11, 13 at 14:55

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