Sunday, March 29, 2009

Prevent Your Blocks from Drying Out

The ingredients of the soil block is primarily composed of peat moss. Peat moss has a tendency to dry out. That is, unfortunately, the drawback of an otherwise excellent medium. But, there are tricks of the trade. First, always let your potting soil rest after you wet it down. This is crucial, because when you come back to it, you'll probably have to add more water. That's great, as that proves the peat was absorbing all that water and now you can top it off with just the right amount to make the "slur". Second, Drying can be prevented by proper spacing. The factory spaces the block spaces tightly together, so when they are ejected, they are touching. This is actually O.K. Leave them close together, under one condition: You transplant them before their roots creep into the block next to them. By transplanting faster you can close the air gap and keep the moisture. I know I said blocks should have 1/8" spacing aroung them, but this is the exception to the rule. Should you want to leave your seedlings in the blocks longer, yes, do go through the extra step and actually pull your newly ejected blocks apart from each other. Third, depending on the tray system you use, always close the last face of the blocks up with a piece of wood. Like a 1x2 on edge, cut to fit the inside of the tray. Air gaps within the blocks are fine, but exposed block faces will dry out quickly, and a dry block pulls moisture from other blocks. I keep all kinds of different sized sticks around to make little wood borders. Plastic trays are actually the best, drop your blocks right up to the edge. Fourth, try keeping your blocks in a shallow tray that can hold water. Fill the water up about 1/2" for the 2" block. This is known as the capillary mat system, and is tried and true at our farm. I use it when I'm going to keep non-root crops a long time in the blocks, like lettuce. Space out your blocks and keep the tray filled with water. And finally, you must water them morning, noon and night. Try using Fogg-it nozzles. You can just drench your seedlings without hurting them. Or, use a gentle water rose attachment or watering can. The main point is to saturate the block and keep it as moist as it was when you made them. Should you be left with extra "slur" after a day's work of block making, I highly recommend you fluff it up with some dry blocking mix until it is slightly moist, almost dry. Then, you can use the slur again without experiencing germination inhibition. Because, the wet slur will start to break down and use up all the nitrogen and produce gases that will prevent seeds from sprouting, or it will turn your seedlings yellow. So, "fluff it up", stir it up, and come back in no more than a few days, or else you should just save it for an ingredient for non-soil block potting mixes and make a fresh batch of slur every time.


  1. Hi Jason,

    This is my first year using soil blocks and I'm having some trouble with the moisture levels. I thought at first that I couldn't really overwater them, but my onions seem to be suffering from damping off and I'm noticing mould (white hairy fluff) growing on / between the 2" blocks that I've potted them on to...any advice? thanks, Deana

  2. Deana,
    Sometimes, overwatering is an issue if there is an unfinished compost in the mix, or not enough peat, coir, or perlite/pumice/sand.
    Cut back watering with that soil, or make an onion soil, with 4 parts peat, 1 part compost and one part sand. Add some lime and rock dust and mist instead of pouring.
    The white molf sounds like mycorrizae fungi and is beneficial, not harmful.