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donald_vargo

Hardening seeding temperatures

last month
last modified: last month

Many of the Articles I've read say you shouldn't be exposing your seedlings to temperatures below 40. I disagree obviously I don't want them to freeze but if it gets down to 34 or 35 I think that's good. I can't imagine why never to your plants get as cold as they might get the first week or two is a good idea? I really love my peppers and tomatoes and I want to harvest asap. Because of this I always put them in the garden a couple weeks before last frost if the forecast permits. Almost every time there is a frost I simply cover them and throw in a heater or two if it's getting that cold and I have blankets if needed. My point is I want my plants to be able to handle 34°. I am only talking about tomatoes and peppers. Do you think I should let the seedlings get into the mid 30s or should I keep them above 40?

Comments (17)

  • last month
    last modified: last month

    I think we're talking about stunting rather than killing. They stop growing entirely when it gets very cold. My experience is that once the temperature moderates, they perk right back up, assuming it hasn't been cold for a long time. I would regularly plant out tomatoes very early because they have to mature before it gets hot here. Once the heat sets in (June-ish), they're done. It's a race. So, amusingly, the threat of cold is large here in the south.

    Donald V Zone 6 north Ohio thanked daninthedirt (USDA 9a, HZ9, CentTX, Sunset z30, Cfa)
  • last month

    IME there's really no point. Like dan said above, it's more an issue of stunting, plus you're also running the risk of the roots rotting out -- where I am, the soil is still relatively cool in early May, a couple weeks makes all the difference. Soil temp very much matters, and if the soil is cool and wet = rot. There's been years where's it's rained almost a week straight in May, you just never know. So why would I want to risk it?


    I start taking the transplants outdoors on the patio in early May, weather depending, to start hardening them off and getting them exposed to the stronger sunshine after living under the lights for a month or two. After they're hardened off I won't bring them back in the house at night unless a frost is predicted, but I do wait until mid May (usually 3rd weekend) to plant.


    Melons don't get planted out until 1st week of June. If the soil isn't sufficiently warm, they balk.

  • last month

    I tend to harden off seedlings in their pots. I have an enclosed porch and use greenhouse caps outside to help that along. But I tend not to plant out in the open beds till soil temps are good. And the plants are full hardened off. I prefer not to push plants to stunting levels if I can help it. I don't get any gain or timing off the plants from doing so.

  • last month

    Very good info! I have to think about this. I had problems with my peppers last year and this might have been 1 reason. I do not mind covering with blankets and adding heat. It is worth it to start harvesting early, if that is what happens.

  • last month

    That's a fair point about considering soil temperatures. I never worry about soil temperatures, because on the last day of likely freeze, my soil temps are already 60F.

  • last month

    I harden off in pots. They will go into cold frames so that keeps them a few degrees warmer. will have heating matt in with peppers (to warm area no heat soil). If temps will be below 35 I will cover with blankets overnight and add light bulbs for warmth. The NOAA predicts a 90% chance my area will have above average temps the next 3 months. Our average last frost is the first week of May.


    My goal is to harvest as soon as possible. I think that if I plant now, it gets cold in a week and stunts them then warms up I will harvest peppers sooner then if I wait for May. What do you think?


    See the attached forecast. The peppers will rarely, if ever, be below 40 and if they are only for 4-8 hours. The cold frame will warm soil more during the day and hold in heat at night. Couple that with the small amount of heat I am adding and it makes a big difference.


    I do the same in fall to keep peppers producing longer. Most years I harvest in December. Occasionally I have to harvest late November. Never earlier. Or average first frost is Oct 26. My point is I easily keep them a month after first frost so 2 weeks before last frost seems "easy" - especially with expected temps above normal.



    The last 4 days (4/19 - 4/22) are what concern me most.

  • last month

    Been thinking more, I am going to test temperature differences inside colde frame and outside. If I can keep it at least 10 degrees warmer that might make up my mind. I also do not want the hassle of carrying trays in and out, and some are getting big for pots. They are all hardened off and ready to go.


    Yes I realize I am being impatient and trying to justify it. I am listening!

  • last month

    Well, only you can decide if your soil is warm and dry enough for the plants to do well or be stunted. And if you are comfortable with your local forcast.

  • last month

    You can buy a soil thermometer.

  • last month

    Actually, if you're interested in soil temps, Syngenta does it for you. https://www.greencastonline.com/tools/soil-temperature. NIce resource for looking at historical soil temperatures as well. Click on the date range and it will give you choices. Very handy. I assume they do this by averaging over measured air temperatures.

  • last month

    I use my compost thermometer to check soil temp, right now it's 62F at 6" deep so I went ahead and planted corn, squash, and bean seed. I would plant a few tomato seedlings since 80's are expected next week but the wind has been almost tropical storm-like crazy lately. No need to torture them being constantly whipsawed.

  • last month
    last modified: last month

    If they are ready, and you are willing to protect them, go ahead. Sitting in pots does not help them, unless you can move them into larger pots. It is supposed to be quite warm for the next week. Just be aware that 2 and 3 weeks on it may be frost cold and rainy. It is your risk, but you seem willing to push.

    I honestly have not ever had any problems with them stunting with variable Ohio Spring weather, as long as the plants are of a decent size they seem to grow into very large plants when planted on the early side. Small seedlings or seeds are a bad idea. I don't know about earlier production, stunted plants produce quick because they think they are in trouble.

  • last month

    They are in raised beds. I do have a soil thermometer and I am going to do some investigating this weekend, and measuring temps.

  • last month

    Do you see warm weather perennials coming out of the ground? I see a lot of plants early, even the slower Hosta are out of the ground. Dandelions have peaked, lawns are being mowed, The soil is pretty warm. Now weather can change quite a bit in the Midwest. You started your seeds too early it seems, since you have shown a willingness to protect them, I would think planting them is probably better than letting the transplant sit in small pots.

  • last month

    Hostas are out, soil temp is 60 at 4" down. As long as I keep a close eye on them worse case I just add some more heaters. I have a lot of elec heaters of all sizes.

  • last month

    I put tom's and peppers in and built a few more cold frames. Covered now with light bulbs in them to add a little heat. I am able to keep air temps 10 degrees higher than outside. Soil temps 4" down are 55 in AM and 60 during the day. I am sure this will increase with cold frames built yesterday. Lowest forecast is 32 so I should not get below 40 air temps (and only at 40 for a couple hours).


    I feel confident air temps will always be over 40 and soil over 57 (most times 60 or more).


    I think this should be good. We have a cold week ahead then a big warm up. After next week most likely no more temps below 40 until fall.