Adventures in Soil Blocking

Branching Out

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My new capillary mat 'window sill' seed starting trays are really earning their keep. 10 days ago I sowed seeds in 1 1/2" soil blocks, filled the water reservoir, and just left them. After five days I topped up the water, but apart from that they have been sitting outdoors in a bright location where they receive some late afternoon sun and absolutely no tending. The weather has been moderately warm and often windy, and the soil blocks stayed nice and moist no matter the weather. There is a full tray of cosmos with 28/72 seeds germinated so far, and on a mixed tray I even have a gomphrena sprouting (centre photo). In my limited experience I have found that gomphrena can be really vexing to start, so this is a welcome development.

Then on June 23rd I started another capillary mat tray, this time with cosmos 'Daydream' from seeds that I had saved last year. I also sowed' Dwarf Siberian Kale' in a white styrofoam tray, and seeds of a great big yellow marigold called 'Phyllis' on a black plastic tray. These trays were placed on the north side of the house and given a layer of row cover to retain moisture and to temper the drying effect of the wind. This location gets about an hour of morning sun, and then the sun warms the trays again for a couple of hours in the evening. They were left to their own devices, and germination has been surprisingly successful with 10/54 cosmos, 8/14 kale, and 12/48 marigolds poking up through the 1 1/2" soil blocks in just 6 days.

And another tip for sharing: soil blocking tools have plastic pin inserts that make indentations in the top of the blocks for the seeds, and the round depression created with the 1 1/2" block is quite deep. Last week I figured out that if you are sowing seeds such as lettuce, cosmos or marigolds in the 1 1/2" blocks it is best to remove the plastic pins first (they pop out) and just make solid blocks instead. That way you can quickly place a seed on top of each block, and use a toothpick to firmly poke the seeds down into the soil so that they are lightly covered. Large seeds like sunflowers or those that can just be dropped in the hole like kale (brassica seeds are like marbles, and have a tendency to roll all over the place otherwise) work really well with the pin inserts though.
 

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Branching Out

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Our prolonged stretch of hot, dry weather has me starting quite a few seeds indoors again. Lettuce in particular has been difficult to get started outdoors, however is quite predictable when started inside. I have a tray of Green Romaine coming along nicely in 1 1/2" blocks, and some cheery looking basil starts too. The basil seeds came in the form of large pellets, each containing several different kinds of basil seed. I sowed Cosmos Rubinato on the same tray which is not a good idea; the cosmos are now 3" taller than the basil. I will move the cosmos to a separate tray, and place them outside to harden off a bit before planting them in the garden.
 

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Branching Out

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I want to start some fall seeds, but hauling up the plastic shelf and the lights and such from the shop to the office is a pita. I dunno.....
My grow light shelves sit next to our boiler and hot water tank year round, so I guess I am lucky. I suspect that in some capacity I will have seeds on the go year round.
 

Branching Out

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I am on a Robert Pavlis kick lately, having just read his books on soil science and composting-- so I decided to give his seed starting method a try.

On July 21st I placed some winter cabbage, chard, kale, collards, and radicchio seeds on moist paper towels in plastic baggies, and then refrigerated them for a couple of days so they could hydrate. Then I placed the baggies in a dark corner of the basement to germinate. At this point I should have watched them more closely, because the cabbage got off to such a roaring start that they had 3/4" long roots by they time I popped them into 1 1/2" soil blocks yesterday. I managed to use a skewer to make deep holes in the blocks, and then I tucked in the long roots as best I could; hopefully I didn't damage the roots in the process. The collards and chard, however, were perfect with just the tiniest sign of germination visible. According to Pavlis once germination is evident you want to get the seeds in the soil-- ideally sowing them before the seed leaves develop. And interestingly, the chard seeds each had several little roots appearing-- since a chard seed is actually a cluster of seeds.

Now the trays of blocks are sitting under lights, so they won't get leggy when they break through the surface of the soil. Pavlis suggests reducing watering after germination, so I will try to let the soil blocks dry out a bit in between watering. While you don't want them to dry out to the point of desication, with the 1 1/2" blocks there is a substantial volume of soil and they seem to be able to easily go 2-3 days without watering.
 

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Branching Out

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Here are some photos of pansy seeds that I had started on July 24th. The seeds were sandwiched between a clear plastic lid and a damp paper towel; that way if roots begin to grow they hit the plastic, rather than growing in to the fibres of the paper towel. I put five different varieties of pansy seed in a plastic clamshell, chilled them for a couple of days, and then left them at room temperature for a week to germinate. One variety did okay, but the other four were seriously over-developed when I checked on them; it was an absolute mass of white roots. I will still try planting them in to starter blocks or 6-cells, but I will start a fresh round of seeds and shorten my time lines to try to get better results. This is so fun-- and encouraging!
 

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Branching Out

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The seeds that I put in soil blocks on August 2nd are doing well, and are ready to be moved outdoors in to the garden in the next few days once the heat wave passes. Kale, chard, and especially Purple Sprouting Broccoli are thriving; the PSB is shown in the photo on the left, in the tall black 4-cells. I have a new broccoli from Wild Garden Seeds called 'Purple Peacock', which is very unusual in that it is downright frilly (in 1 1/2" blocks on the red tray). For this one Frank Morton crossed 'Green Goliath' broccoli with two kinds of kale. Apparently it tastes good raw or steamed.
 

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Branching Out

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Less than half of my primed pansy seeds resulted in seedlings, however I still ended up with 38 plants so encouraging results just the same. Next time I may put 2 or 3 seeds per block, spaced a little bit apart in case they all sprout. My Green Romaine lettuce is begging to be bumped up; I will have to find a shady spot to heal it in very soon. There are also some Nemesia 'Carnival Mix', and basil from pelleted seed that had a mixture of different varieties. Those will need to be pricked out and potted up (in my spare time!) 🤣
 

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GottaGo

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@Branching Out I've got the 2" blocker on my Christmas list, but how does one 'move' the blocks? Tongs of some sort? Gardeners supply has a seedling tong, but it seems a bit expensive. Would basic smooth tongs out of WalMart suffice?

You experience, please. :)
 

Branching Out

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@Branching Out I've got the 2" blocker on my Christmas list, but how does one 'move' the blocks? Tongs of some sort? Gardeners supply has a seedling tong, but it seems a bit expensive. Would basic smooth tongs out of WalMart suffice?

You experience, please. :)
What a great gift idea! I have long 1/2" wide plastic tongs that are very useful for plucking 3/4" blocks from the middle of a tray; a butter knife works too, but only if the blocks are along the outside edge. Each of these items were sourced from thrift stores for about a dollar. The larger blocks I tend to lift with a butter knife and/or a small metal spatula. Sometimes you have to cut along the side of the block before you move it, if the roots have grown in to adjacent blocks. Do not try to move it if the soil is moist, or the block will disintegrate. As long as the soil blocks are fairly dry they hold together well, and you can often just pick them up with your hands.

What kind of seeds are you hoping to start in soil blocks?
 
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