Hello. I have a 1 year old system that for the most part has done very well over the last year. That said, I've never been successful in growing a good head of lettuce. At the start I figured it was due to the summer temps, then I installed a swamp cooler and eliminated that variable. Now, having gone through the first winter, I can say that I have been experiencing the same issues. The lettuce grows well (speed wise) but bolts. I end up with long stalks and a large leaf spacing (hardly what you expect lettuce to look like). I've tried multiple varieties all with the same results. Other plants, beans, tomatoes, etc. do fine. I have been unsuccessful as of yet in growing sweet peppers reliably.
System details: Chop 2 Murray system (3 grow beds), south facing lean-to greenhouse with five wall Poly roof.
I would appreciate any and all thoughts on what may be the issue.
I've rarely ever gotten full closed heads of lettuce but I live in FL and even this winter has been too hot to grow dense closed heads of lettuce since we have been only getting a few days at a time of cool weather. I generally give up growing lettuce for about 1/3rd to half of the year and I find I do best when I choose varieties that do well with warmer weather. Summer crisps and some butter crunch. Good light along with cool conditions seems to be rather important in my experience at getting dense colorful growth on the lettuce. When they get too much shade they tend to be leggy then bolt instead of heading up.
I have had the same issues... a look around the forums and gardening sources seemed to indicate that lettuce commonly (but not exclusively) bolts when there is insufficient light as TCL noted. More access to light may well work... but in the meantime, I reburied leggy lettuce even deeper and they seemed to respond ok and I had better results. Hope that helps.
heat and dryness is the main issue... lack of exposure to light isn't an exclusive cause to bolting... even in the hawaiian summer the lettuce would bolt, and during that summer it's hot, dry, and sunny.
bolting is a defense mechanism... it can be cause by just about anything that threatens the procreation of the lettuce... too hot, too cold, too dry, excessive sunlight, too little sunlight... really lettuce is a pampered princess...
How warm does it get in the greenhouse during the day? Try to keep it cool -- vents & fans will help a bit but if it's too warm then it will bolt regardless. We're at 6400' (western Colorado) and our lettuce has been amazing (our 1st winter growing in an unheated greenhouse) but the arugula has bolted.It's been as low as 16 (in the greenhouse) for a few nights but will heat up quickly during the day. I've grown lettuce outside here in the summer but have to keep it shaded with row covers as the sun is too intense for it. We have a Chop 2 system as well as a Friendly DWC system and the plants in the Chop 2 are amazing - but only the lettuce enjoyed the DWC system this winter - everything else just went into hibernation. Could be we started them too late to get any real growth going before the daylight got too short.
This was an experiment for the winter and it has been so amazing to go harvest greens in the middle of snowstorm!! Our neighbors are clamoring for our veggies!! Can't wait to see what the longer days will bring!
High nitrate levels certainly tend to keep many plants growing lots of leafy green but lettuce is generally a very low nutrient demand plant so I would say you need to have nearly 0 nitrate in order for the lack of nitrates to be the cause of bolting.
Granted, my experience is from a sub tropical climate but this winter I've had some very low to even no nitrate conditions in some of my systems and the lettuce is not bolting from it.
it's kind of funny actually, for all the systems built around mono-cropping lettuce it is the one plant that i can't seem to grow well! i've given up trying to eat the lettuce in my bed and try to convince myself it's just there to feed the bugs. it really does seem to be quite finicky about its growing conditions!