LED First Harvest

I picked some of my first batch of lettuces last night from under the LED lights.  I had them tested by Everiss Labs and since this was the first time I’d ever seen tissue test results, I was a little concerned that the nitrogen levels were a little high and the calcium levels a bit low.  Although I had no direct way to tie these percentages to the ppms that are used to measure the nitrates/nitrites when scientists talk about the issues of low light lettuces, I thought this might indicate that the plants had a problem with high nitrate/nitrite levels that would make them unhealthy to eat.  However, when I asked for clarification from the lab, they said absolutely no problem, not to worry.  The averages weren’t meant to delineate healthy ranges, just averages from plants over the years and my marginal variations weren’t significant.

I had wanted a worst case analysis for the testing, too.  I’d fertilized them 24 hours before the test (Scotts Miracle Grow again).  I don’t think they really needed it; this was part of the test plan.  And since I read that nitrogen levels go higher at night, picking my sample first thing in the morning would have helped make it worst case, too.  From now on, I will not fertilize for a week or two before harvest and always, only the minimum necessary.  The second batch, already under the lights, is made with a combination of ProMix and compost; I’m hoping that will have everything the plants need.  And I’ll harvest in the evening, after a full day of light; the lettuces may be sweeter that way.

To the right is a shot of the sample that I sent to the lab (bottom), and remaining plant.  Notice the strong root structure; air pruned because of the soil blocks.  I expect these may bolt a little earlier than lettuces with all the root space they need but we’ll see.  With a new flat started and a pot of basil to go under this same light, I am at or above the space limit so some of them have to go, anyway.

Another possible, very low level symptom of high nitrogen stress, that I actually had to look for, is leaf tip burn.  What I found was on a couple of the older leaves and when it’s really a problem, I read, it’s on the inner, newer growth.  But it is related to low calcium in the tissue.  Low calcium uptake is associated with the low light (high nitrate/nitrite) issues of lettuce, and while this is so marginal that it’s not really a problem, I thought I would post a picture.  Since most of us are judging plant health from observations, it’s good to know what to look for.

From seed to the table in eight weeks is a happy outcome, in my opinion.  I’ll stick with leaf lettuces for now but work on more variation in my harvests.  And probably smaller batches so that I have a few plants ready at any point in time.  For more information about timing and processes, see the category LED light growing or ask a question in your comments.  Sharing is half the fun.  The other half is eating!  Fresh and healthy from “the farm” to the table.