How to grow lettuce using the Kratky method

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How to grow lettuce (and anything else) using the Kratky method of fill and forget non-circulating hydroponics.

Kratky grown lettuce

Materials needed:

  • Tote – The capacity needs to support a minimum of one gallon per plant. Also take into account you will lose some volume between the lid and net cups, unless have a tote with a raised lid. So, for a 10 gallon tote, six plants is good.
  • Lettuce seeds – You can get these anyway, lowes, walmart, etc… or amazon and ebay. They are very inexpensive, usually 1-3 thousand for two or three dollars.
  • Net cups – I like using the three inch net cups, but you can use whatever you have.
  • Hole saw – If using the three inch cups, a three inch hole saw (and arbor) cuts the perfect size. This is not necessarily true for the two inch cup and two inch hole saw, unless you get two inch cups with wide lids.
  • Grow sponges – This is to hold the seed until it germinates and sprouts. You can use peat based sponges like what AeroGrow and Park Seed sell, or rockwool. Rockwool needs to be pre-treated to lower the pH. I using the 6-0 refill size biodome sponges that Park Seed sells. These cost around 18.00 for 120.
  • Growing medium – This is to anchor the plant, you need something with good aeration. Clay pebbles (hydroton) or coco coir chunks work great.
  • Nutrients – Check with your hydroponics store, or search online. Most will work fine, like Maxibloom, Maxigrow, Dyna Grow, etc… I use a mix of MasterBlend, MgSO4 and Ca(NO3)2. More information on that here.
  • Grow light – T8 shop lights are fine. I personally like the Utilitech brand that Lowes sells, because the housing is so narrow that you can fit three side by side on an 18″ shelf. Try to get the daylight spectrum bulbs. CFL and LED lights work great too.

Steps:

  1. Drill holes in the tote lid using hole saw. For three shallow 10 gallon tote I made six holes.
  2. Place sponge in the net cup and fill around it with grow medium, i.e. Clay pebbles, coco coir, etc…
  3. Place a small pinch of seeds (3-5) in the top of the sponge. It should have a small hole in the top for seeds
  4. Put the tote in place where it will stay and fill with nutrient solution. It should come up to a half inch to an inch from the bottom of the net cup. You can place an empty net cup in there to check the water level.
  5. With the lid secure, place the filled net cups in the lid.
  6. Turn on the grow lights and leave them on 24/7 until the sprouts come up and produce at least one set of true leaves
  7. Once the sprouts are strong enough to stand on their own, start thinning them down, eventually to just one per net pot. If there are several, this should not be done all at once.
  8. When the individual remaining sprouts have matured and have at least a couple sets of true leaves, put the light on timer and run 10-12 hours per day.

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Here’s a video of the process:

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