See:
Link: forums.gardenweb.com/forums/load/lights/msg0319125925834.html
No real shock for me with the experiment that was discussed in that thread. I keep my lights on 24/7 for my seedlings as well and the difference is truly remarkable with how much more they grow.
My only problem with it is that when I put my seedlings outside in late mar, early apr (I bring them in once or twice), the sudden decrease in day length makes them think it’s winter. So the leaves yellow, BS and drop and the seedling forms buds “for next season”…even old, mature roses display this response. It takes them weeks to figure things out and go back to growing (right during the best of the growing season).
This is the second (or more) year this has happened to me. I’m not sure if I should starve them of light for a few days or what next time to shock them into correcting this condition.
Jon, wow…that is interesting. I have never had that happen to my seedlings once I take them outside. I am zone 6b (southeast PA) and I take my seedlings outside in mid to late May (depending the temperature trends). I actually keep them out of direct sunlight for a few days since it is stronger than the artificial lights they were under. The only time I have lost leaves is when I get them in to direct sun too fast and they are essentially sunburned and then drop.
Maybe the response you are experiencing is more related to temperature than it is to light??? Just a thought…
I would think the same perhaps but I usually put them out when my outside roses are starting to leaf out. I’m in TN, we had 80’s mostly and even 94-96F for a a few days back in Apr . I usually wait for the night time lows to be around 45f, I bring them in if it gets much cooler. Maybe there is enough day length between Apr and May to make a difference?
Oh, what’s interesting is that it doesn’t do it to the late sprouters…the ones that are only a few weeks old.
Any chance that this is happening mostly to older seedlings that may be getting slightly root-bound?
Seedlings that have not developed their cell structures under direct sunlight need to be acclimatized more slowly to direct sunlight, so that their leaves can thicken, along with their cell structure. this would account for the younger seedlings adapting successfully-they have not become fully acclimated to the artificial light and adapt much better and faster. However, many species of plants are slow to acclimate and need that slow adjustment-i.e., being placed on the east side of a structure that will shade them after 2-3 hrs of exposure, and only allowing A.M. exposure which is much less likely to shock the seedlings, and give them a week or two to thicken their cell and leaf structure. If the sun is especially hot, it may take a little longer for them to build up adequate protection. Kinda like the first trip to the beach on summer vacation and not wearing any suntan lotion-if you don’t have any protective melanin (acclimation) you too will burn. If you transfer them outdoors earlier, when the sun isn’t as intense, or during a cloudy, overcast week, they will still acclimate and can withstand much longer periods without suffering setbacks.
No, I usually put at least some of them in fairly large pots. It’s late May now and most have recovered…so it took to early mid-may for them to start vegetative growth again which is exactly when Michelle let’s hers out. This year I am going to hold out long as possible to plant and sprout them so I can perhaps put them out later and see if that does the trick.
Actually I take that back some ARE (slightly) root bound when I re-pot & some of it could be transplant shock (because I usually transplant right before throwing them out). Also, I know this year it rained more times than not so that might have an effect because the soil doesn’t have time to dry.
I moved 500 seedlings outdoors this spring, very gradually exposing them to increasing levels of sunlight over about two weeks time. Some cultivars were undaunted but, despite cool weather and lots of tlc, mature leaves on most of the plants generally suffered severe sunburn. Emerging leaves fared very much better.
From this experience I think that the transition period actually allows only newly emerging leaves to ‘harden’ in the manner Jackie describes. I doubt that mature leaves of roses can be acclimated from artificial light into daylight without damage no matter how gradually the process occurs.