Potting On & An Adjustment to the Wooden Tray Length

Potting On

Potting On, or transplanting seedlings from smaller pots to larger pots, is a tad different when working with soil blocks. In traditional transplanting, seedlings have to be gently removed from smaller pots, and replanted in larger pots. It involves a fair amount of handling of the plant, and requires assuring enough soil is in the bottom of the pot to keep the transplant at the top of the pot. The great thing about soil blocks, however, is that potting on consists of nothing more than dropping a smaller block – with the seedling in it – into a larger.

Earlier this season I started seeds in 3/4″ cube soil blocks. I re-potted those seeds that sprouted in 2″ cubes. Recently, many of those transplants have grown enough that I have needed to transfer them into 4″ blocks. From there, they’ll go into the ground.

My earlier soil blocks were made with a specially formulated potting soil called 512 Mix, available from Johnny’s Seeds. (See Introduction to Soil Blocking.) When I ran out of 512, I found some local potting soil also, formulated for making soil blocks; Fort Vee, made by Vermont Compost. Both brands are recommended by Eliot Coleman. The Fort Vee is much lighter, having considerably more moss in its blend. In fact, it’s so light I would doubt its ability to nourish seedlings were it not for Coleman’s recommendation.

On the other hand, I like that it is so porous. It does not pack down as hard as the 512 does after a few days of watering. That may mean it is easier for the seedlings to develop strong root structures – time will tell. In any event, I tried mixing the two blends 50:50, which was interesting. But I prefer a 25:75 ratio, with the 512 in the minority position.

I’ll be watching to see if there is any appreciable difference in plant growth or root development between the two mixes and the various ratios using both.

Yesterday and today have been beautiful, warm days in Vermont, which means I had to work outside. Here are some photos from my second day of potting on.

My Potting Station on the deck, surrounded by trays of seedlings catching the sun.
I found the soil doesn’t compress enough in the top of the 4″ block unless I help it. That’s probably either because I am not making the soil wet enough – which I doubt; wetter soil sticks inside the form and fails to form good blocks – or because I don’t make enough soil to be able to press down into it and completely fill, and compress, the soil at the top of the form – which is more likely. (I’m okay with this slower method for this year as I work my way into the process; but next year I’ll want to be more efficient.)
Placing a soil block in the tray. Note the long side board has been removed to make it easier to work. I’ll also remove the side when I’m transplanting, and use a dry wall spatula to pick up the blocks.
Replacing the side board. I’m currently using wood screws, but next year I’ll switch to small hook-and-eye arrangements to make this process fast, easy and secure. Replacing the sidewall slightly compresses the blocks – which helps to keep them from drying out.
Potting on. Here I’m dropping a 2″ cube into the rightly-sized hole formed by the 4″ soil block maker. If you look closely you can see the 3/4″ cube centered in the top of the 2″ block. Notice, also, the 2″ gap between the 2 soil blocks and the tray’s end wall. Imagine all of the moisture evaporating off of those large sides! That’s why I made some new, shorter trays. (Read the section on tray length changes below these photos.)
Misting the completed transplants. I use a very light mist setting because the blocks have not “set” and could wash away under a heavy watering. (Behind me, through the trees, you can see portions of my garden plot, which I tilled by hand with a stirrup hoe. And on the left wall of the shed you can see a white box: that’s the first of my replacement bee colonies, arrived last Saturday. But please don’t notice the untrimmed new shed shingles – I just haven’t gotten to them, yet!)
Another view of happy seedlings stretching their roots and catching some rays.


Wooden Tray Adjustment

I made a minor change in the wooden trays. (See Making a Soil Block Tray) Coleman’s directions call for trays that have interior dimensions of 18-3/4″ x 8″. That length is great for the 2″ cube soil blocks – in theory it allows 4 rows of 9 blocks, 36 total. I have found I can place 10 in a row by slightly compressing the blocks (which tend to be just a tad under 2″). I like to do that because I think it does a better job of keeping the blocks damp.

However, when the trays are used for 4″ cube blocks, the sizing leaves a 2″ space at the end. I have used that extra space for some younger plants in 2″ blocks, but as all of the seedlings get more mature, I don’t either need or want the extra space. Open space lets soil blocks dry out faster.

So today I made a new set of trays that are 2″ shorter; with an interior length of 16-3/4″, they are sized to fit 2 rows of 4″ cubes, 8 cubes per tray. There’s enough extra space to allow the soil block maker to drop the last block in each row without damaging the block beside it.

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