Why I’ve been Underfeeding My Hydroponic Lettuce

I’d been thinking for a while that my lettuces and herbs were growing slower than they should. They’re 3-4 weeks old but they just weren’t as big as I’d expect. You’re supposed to be able to harvest lettuce in around 35 days from seed. But my lettuce looks like this:

Lettuce at 3-4 weeks old. Growth looks like much less than I expect at this point.
Lettuce at 3-4 weeks old.

Definitely not the abundant harvest I was hoping for. I’ve been giving them a diluted nutrient mix thinking that they needed it since they were still young plants with something like 1/4 to 1/3 tsp or less per gallon of the Maxigro nutrients. It wasn’t until someone mentioned nutrient feed charts in a forum that I realized my mistake.

For Maxigro in a recirculating system like the one I setup here in the small Home Depot bins with the airstones, this is the feed chart: https://gh.growgh.com/docs/Feedcharts/GH_Maxi-REC_03216am.pdf. (You can find the full list of feed charts for this brand here: https://generalhydroponics.com/feedcharts).

From the feed chart, they start out at half a teaspoon per gallon the first week and move to the lower recommended dose on the package of 1 teaspoon per gallon the second week! I was worried about some of the issues you can get from overfeeding like tip burn but I was definitely overly cautious this time around.

The lesson I learned from my mistake this time around is to make sure you’re checking the feed charts for the nutrients you’re using. Otherwise, it’s hard to know what concentration of nutrients you should be at each week.

To try to fix the problem, yesterday I dumped the old nutrient solution and made a fresh batch for each bucket so they now have the recommended dose. I’ll update you in a few days on how the plants do now that they have the nutrients they need. Hopefully this will increase their growth enough that I’ll still get a decent harvest of lettuce.

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