indoor to outdoor hardening

December 5, 2019


I'm planning my very first small garden (mostly bucket pots) and would like to begin growing seeds indoors sometime in January or February, then transfer them outdoors once the weather warms up. I have not decided whether I'll germinate them by the window or under a grow light, TBD. Seeds will include alpine strawberries, tomatoes, and various annual and perennial flowers. Maybe I'll try sweet peas, too.

What concerns me with the research I've done, is the concept of hardening off / tempering the seedlings to the outdoors once ready to go outside - the recommendations are to increase outdoor exposure gradually.

How am I supposed do this with a full-time job?

I'm in zone 10a. Earlier this year, I learned about this the hard way, lost a couple avocado treelings. Most survived, but have unsightly burned leaves :(

Thank you for your time!

Comments (12)

  • floral_uk z.8/9 SW UK

    In your zone I'm surprised you need to start anything indoors. I think you'd just be wasting effort and money. And some of your seeds needed starting last autumn if they are to flower before your heat hits. Sweetpeas and alpine strawberries for example.

  • kitasei

    The OP's zone doesn't show up for me so I am guessing you are in a warmer area than I (6b) so this likely doesn't apply. But my first thought is why not wintersow the hardy annuals and perennials? You'll spend a winter Saturday making your milk carton greenhouses, put them outside and forget about them til spring. There's lots of information available on how to do this. As for the tomatoes, my experience every year is that I can't resist starting them too early (inside, now with grow lights), and putting them out to early (on those seductively warm days) They inevitably go from promising to stunted. The seeds I direct sow once the soil warms up have ALWAYS outperformed them. Will this stop me from trying again? Probably not, but not for any rational reason.

  • j

    Interesting, thank you for the feedback. Various seed instructions say to wait until specific temperatures are met outside before direct sow. Since the last couple winters here have had cold nights for longer than usual despite my zone (10a, coastal southern california), I'm anticipating it a trend and maybe this coming year will be the same. The lows have ranged from low 40F to high 50F from January to April, with an occasional warm night and day. The warmer-end of temps (highs in the 80F, occasionally into low 90F) haven't arrived until late July to mid-August.

    I have limited yard space, so everything would be in containers (pots and buckets).

    I will research milk-carton greenhouses, never heard of this, thanks.

  • floral_uk z.8/9 SW UK

    Those temps are plenty warm enough to start sweetpeas, strawberries and many annuals and perennials outside. As kitasei says you can sow hardy plants outside using winter siding methods. Or just sow them in pots as normal. The tomatoes might need starting inside but won't need to be indoors for long.

    j thanked floral_uk z.8/9 SW UK
  • ken_adrian Adrian MI cold Z5

    the term is HARDENING OFF ....

    and it variable across all the plant culture variables ...

    you seem to only be thinking about temp ...

    imo... sun is the most important variable ... all indoor light is much less intense than sunshine .... so the plants go out into full bright shade ... no direct sun at all ... for a week or so ... then a week in sun in the mornings.. or evenings ... and then.. eventually ... into full sun ...

    as to temps ... it will depend on how warm your house is ... in the trades ... they just start openning the greenhouse panels.. and acclimating the plants to colder temps .... so you need to do the same ... start coolling them off if you can .... perhaps ina garage ... if you open the door for a week .. and close it at night ... you can temper them off to cooler temps ...

    as to water ... keep in mind.. cold media .. when the pots are cold.. water will not disappear as fast ... so you can probably reduce water ..and water only when the media needs water ... it will al change as you go outside ...

    cold damp media.. or even once planted in the ground... will slow growth down ....

    i dont know if i would try strawberry by seed ... i am sure it can be done ... but the plant is [depending on what kind you are dealing with] .... but the fruit bearing ones are more like a biennial .... two seasons to fruit.. and then that crown dies ... but runners are sent out... for the future .. again.. depending on which ones you are thinking about ... imo .. it just might be easier.. to insure a crop... to buy some plants ...

    this also falls into the common name issue ... you get your best info.. when you use the most specific name ... and in this example.. strawberry is just to general a term.. for us to be very specific ...

    good luck.. have fun.. keep us posted ...

    remember.. cold is not only a severe cold will kill some things.. but cold also slows everything down .. sometimes almost like a suspended animation


    ps: without pix and in the moment info.. it would be very hard to determine if browning leaves were a cold event injury.. or a sunburn injury ... so you have to figure out how to deal with both variables ...

  • zen_man

    Hello j,

    " I will research milk-carton greenhouses, never heard of this "

    There is a Winter Sowing forum here. Some people are very enthusiastic about Winter Sowing. There is also a Winter Sowing forum at the National Gardening Association

    I much prefer to grow indoors under lights during the Winter, because you can't see through the milk cartons to see what is going on.


  • j

    Great input and feedback, much appreciated. There are enough seeds to try a few outdoors and a few indoors. I will certainly try sowing a few outdoors. I now see why the suggestions would be in fall, since it had been warmer and would have helped germinate the seeds. Technically it's still fall, but it has cooled off suddenly.

    Back to my original question: how do people harden off their indoor-germinated seedlings to plant outside, if they have a full-time job? I can do a 1-2 hour thing in the morning and waltz in a bit late, but any longer and it gets tricky. I was thinking possibly taking a friday and a monday off, would 4 days be enough? Or am i better off just finding a different way to grow these plants?

    Thanks again for your time.

  • zen_man

    Hello again, j

    " ...how do people harden off their indoor-germinated seedlings to plant outside, if they have a full-time job? "

    Well, I am retired, so you could say that my zinnia hobby and gardening are my full time job. But a lot of things are going on, both inside and outside, in the Spring, so time is of the essence in the hardening off.

    Here in Kansas the big shock from going indoors to outdoors is in light level, not temperature. The indoor seedlings are used to a light intensity of 500 foot candles (maybe less) to probably no more than 1000 foot candles for really good lighting. Full sun here can be 5000 foot candles, so the big danger is literal sun burn. I move my indoor pots to a spot outdoors that doesn't get full sun. Our north deck is fully shaded, or under a big lawn tree for a very limited amount of full sun. Keep an eye on your seedlings in case they need a spritzing with some water from the hose.


  • Labradors

    What Zen man says.

    I would suggest that you start on the weekend, putting them out for an hour or two in a shady spot. After that you can leave them out during the day in the shade, having watered them first.

  • kitasei

    That’s why I suggest wintersowing. They acclimate themselves.

  • sharon2079

    I live in zone 10 Florida.... and when I harden off my plants this is what I do..... Normally I try to pick a week that isn't suppose to be terribly windy. I will take the plants out first thing on a Monday morning and place them in a shady location while I go back and get ready for work.... I then bring them back in the house before I leave. If I get home before dark I take them back out and place in a shady location and leave them to dark. After a day or two I leave them out all night. By the weekend I then move the plants to a sunny location, but I normally place a slated chair over them so it gets some direct sun, but it is filtered. I check on them throughout the day to make sure they are not wilting... if they are I move them back to the shade. By the next weekend they are ready to plant.... if the plants are snapdragons or pansies that are truly cool weather plants, I will keep the chair over them after they are planted until they have a chance to get established.

    Even though I am zone 10 I will start quite a few plants inside.....

    j thanked sharon2079
  • j

    Thank you, @sharon2079, you've given me a great place to start. I can time the morning and evening exposure, in the week, then increase time over the weekend when I'm actually home and can monitor.

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