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I planted a number of vegetable seeds (zucchini, cucumber, peppers, kale, etc.) indoors in 1"x1" pods. They germinated quickly and well. Once the true leaves appeared, I moved them over to a 4"x4" container with potting mix. The plants look healthy but they are not growing as fast as I would have thought. I now leave them outdoors (in the shade) and have been out there for about 4 weeks. What else should I be doing so that they can grow and I can move them to my vegetable raised bed?

  • What's your usual daytime temperature now? If it's still in the 50's (10°C), you'll not get much growth, except for kale. You might do better putting the warm season crops on a warm, sunny windowsill, inside. – Wayfaring Stranger Apr 1 '16 at 1:29
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I'm by no means an expert, however I am pretty sure that, at least for Zucchini, Cucumber and peppers 1% more light = 1% more growth. Thus in order to increase growth, maybe you should start moving these into full sun.

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    Yeah this is pretty much it...until you pet you veg out into the full sun along with plenty of water and nutrients they aren't going to get that signal to start growing fast. It's a hormone that is triggered by light, and it's also one reason to not plant indoors TOO early. Once a seedling gets too old, it won't ever get the signal. – Escoce Mar 31 '16 at 14:02
  • I have it outside but is sitting in the shade and is getting plenty of light, just not direct sunlight. Does that change your comment? – JStorage Mar 31 '16 at 20:10
  • Nope. More light=more growth. Full sunlight will give you more growth then partial sunlight. I note that I am only commenting on the Zucchini, Cucumber and Peppers - I have no knowledge of the other plants (yet). You should also follow GramChiu advice about hardening off your seedlings. – davidgo Mar 31 '16 at 22:25
  • More light is generally good, especially for squash, but if they're still in their pre-transplant containers, it may hurt your plants to give them too much sun. – Shule Feb 4 '18 at 2:02
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You need to harden your seedlings now so that they are ready to be transplanted into your garden bed. Since your pots are on the small side, there's a risk for some plants that they'll get the signal to start bolting.

This video from the biointensive grow method explains the transplanting process. They advise using 6 inch deep flats, wait until the plant is 6 inches high, and transplanting in a hexagonal pattern to maximize soil use.

  • What does "start bolting" mean ? – davidgo Mar 31 '16 at 0:24
  • It means sudden shoot/stem extension or sudden increase height. It is usually caused by new cells becoming highly elongated. – Jim Young Mar 31 '16 at 0:56
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    bolting happens when the plant "thinks" it has reached adverse growing conditions and needs to start reproducing immediately. So, it starts switching to flowering and seed formation, not what you normally want for your lettuces, cabbages etc. Leaves often then become bitter to taste. – Graham Chiu Mar 31 '16 at 1:06
  • Thank you - very interesting. That also probably explains something I saw earlier today on my lettuce or spinach in the kitchen ! – davidgo Mar 31 '16 at 1:41
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Seedlings (from my observations in my area) don't tend to grow very fast outside in containers in the spring, when exposed to the raw outdoor air and light. They seem to require more warmth. I don't know how warm your area is, though.

However, if you can put a humidity dome over them outdoors, that should help them to grow faster (provided there's nothing wrong with the plants or the soil). You can make a humidity dome out of an empty milk jug. Throw the cap away (air and circulation is important), cut the bottom off, and put it over your plants (make sure wind won't blow it away). Plants grow faster under them until it gets too hot to use them without killing them. When it's hot enough to germinate cucurbits via direct-seeding, you should probably think about removing the humidity dome soon, if not right away (or at least widening the hole to let more air in and prevent the sun from cooking the plant).

I suppose it's possible that the plastic of the milk jugs filtering out UV rays would help the plants to grow faster. The increased warmth would certainly help (the jugs will even protect from frost). The protection from wind and pests would also likely help.

Kale should be able to handle cool temperatures better than the other kinds of plants you mentioned and so should be in less need of a humidity dome.

  • Thanks. I am in San Francisco area so temp these days is about 60f which I would think is good for seedling growth. I will try your suggestions as well. – JStorage Mar 31 '16 at 16:10
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    60°F is still quite cool. The optimal germination temp for most garden plant seeds is 68°F. After a hardening-off period, move your plants into the proper sunlight conditions. Monitor their growth when the daytime temps are mid 70's to 80 & you should start to see some pretty good growth. If you don't get good growth, it may mean that you planted indoors too early or that your soil lacks sufficient nutrients. – zeffur Apr 1 '16 at 23:15
  • I actually recommend direct-seeding cucumbers and zucchini. It can be easy to stunt cucumbers and some kinds of squash when starting them in containers. Cucumbers grow easily when direct-seeded. Starting peppers early can definitely be very helpful, however. – Shule Apr 2 '16 at 18:50
  • I should note that my previous experiences with transplanting cucumbers and squash were with plants grown extra early under light indoors. I imagine you can do it successfully if you do things somewhat differently than I did (like start them in an unheated greenhouse instead, and not as early as I did). – Shule Feb 4 '18 at 2:06

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