Adventures in Soil Blocking

jojobeans

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Of all of the flowers that I have tried to grow from seed, annual phlox has been the trickiest. They are kind of my nemesis. Phlox has been hard to germinate, and not very easy to grow-on either. Last summer there were only a handful of plants that made it to bloom--but in the end they were gorgeous. I saved about a tablespoon of seed, and I am stunned to report that those seeds sprouted nicely for me after just a few days. I had them under a little piece of damp paper towel in a cup in the fridge for about 24 hours, and then in a dark kitchen drawer for about 5 days (since phlox seeds really need complete darkness to germinate). Today I poked the seeds in to 3/4" soil blocks, and I am cautiously optimistic that they will grow.
Just wanted a follow up on the phlox. Did you put the blocks on heat mat, covered or uncovered? Do you see anything happening yet. After reading your post I popped my seeds in the fridge and took them out this morning. Are they on a damp paper towel/baggiie in the draw?? What else have you soil blocked. I love soil blocking.
 

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Just wanted a follow up on the phlox. Did you put the blocks on heat mat, covered or uncovered? Do you see anything happening yet. After reading your post I popped my seeds in the fridge and took them out this morning. Are they on a damp paper towel/baggiie in the draw?? What else have you soil blocked. I love soil blocking.
I have yet to use my heat mat this year, relying instead on warm room temperature to germinate the seeds. Some folks believe that phlox may even benefit from alternating day/night temperatures, so it may be better to have the house cooler overnight.

After I took the little plastic cup out of the fridge I placed it in a kitchen drawer with a black plastic take out cup over top, so no light gets in at all--except when I check on the seeds once a day. If the little piece of paper towel that is covering the seeds is not damp enough I put just a few drops of water on it (you don't want the seeds to be sitting in water-- just nice and moist), and then back in the dark drawer it goes. The first batch spent 5 days in the drawer before I saw signs of sprouting. I am on round two of phlox seeds now; it's a different variety, and those seeds have been in the drawer for 7 days. The seeds are swelling, but have not germinated yet.

Phlox can have a very hard seed coat, so pre-sprouting the seeds will also reduce the chance of the seed coat sticking and not releasing. Here is a helpful article on growing Cherry Caramel Phlox from seed: https://thekokorogarden.com/blog/20...mel-for-flower-farmers-and-the-cutting-garden
 
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I was looking back on an experiment that I did last winter where I started lettuce seed in 3/4" blocks vs. in homemade blocks that were about 11/2". After 25 days the seedlings in the larger blocks were massive, and the ones in 3/4" blocks were still very small. (See my February 20, 2023 post in the thread Growing Greens Indoors Under Lights). Given that the difference in size was so dramatic, I decided to make more of the larger blocks for starting Kalura green Romaine lettuce seeds. I filled my styrofoam Lee Valley seed propagation tray with moist blocking mix, packed it in firmly, inverted it on to a cafeteria tray, and then used a cork to push down on the blocks to release them. The blocks are spaced well apart on the tray, which should provide ample room for the lettuce seedlings to spread out and grow for about 4-6 weeks. The lettuce seeds had been pre-sprouted for a couple of days and were already showing signs of germinating. I made a little hole in the top of each block with a skewer and then poked one lettuce seed in each hole-- and that's it. This tray will stay in our warm living room until most of the cotyledons emerge, and then it will go to the cool basement to continue growing under lights.
 

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This tray is the poster child for why it is a very good idea to pre-germinate seeds. On January 27th I sowed three kinds of lettuce in 1 1/2" blocks without pre-sprouting them: Kaiser MI, Prizehead, and Leny. It is now February 6th, and of the three varieties only Prizehead is thriving. The other two have occupied prime real estate under the grow lights but have little to show for it apart from a few weak seedlings. This is what happens when you do things in a hurry, instead of taking a couple of days to make sure the seeds that you are sowing are viable and vigorous. Seeds that I pre-sprout before sowing tend to emerge at the same time for the most part, resulting in a much more uniform tray of seedlings.

Of the three lettuce varieties, I believe that Prizehead is the only heirloom and it is one that I hope to save seeds from this year (last year I planted it, but it is a cool season cultivar and the heat of summer took it out). Victory Seeds indicates that it has been around in seed catalogues since 1881, https://victoryseeds.com/products/prizehead-leaf-lettuce
 

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10 small containers with seeds tucked under a square of damp paper towel, placed in the fridge to begin hydrating. The seeds include early cold-tolerant tomatoes, peppers, some lettuce, Bolero peas, and spicy bush basil-- which is a dwarf variety. In a day or two they will move from the fridge to the kitchen counter for germination. Some of the seed has been around for a couple of years; if it doesn't sprout I will just toss it, rather than storing it any longer.
 

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On January 6th I started a bunch of early cold-tolerant dwarf tomatoes in 3/4" blocks, and after just a week they all got bumped up to large blocks that I formed using an empty 2" pot. The large blocks shown here on the red tray sustained the seedlings for five weeks, at which point they needed more room to stretch their roots to continue growing. Moving the large blocks to tall containers was easy, because you can just drop the block into the bottom of the pot and then fill in soil around it; there is no root disturbance at all. It is important to note that the larger containers will take up about three times more space under lights than the tray of soil blocks did-- so when I start my main season tomatoes it will be wise to time them so they can move outdoors to the high tunnel at the 3 or 4 week mark, or else I will be completely over run with large seedlings. And interestingly, even though these were all started on the same day there is huge variation in their growth habit. One of the smallest micro-dwarf cultivars 'Andrina' is still just a couple of inches tall, while others such as the robust 'Kalinka' are already 6" tall.
 

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Starting pepper and tomato seeds for our friends' community vegetable garden is often a team effort, with me sowing large soil blocks of seeds that then go on a heat mat at the home of the head gardener to germinate. Once the seedlings are a couple of inches tall they go in his greenhouse, which he keeps heated to about 15C(60F); he does not have grow lights apart from some small lights about the heat mat, but the greenhouse is plenty bright for starting seedlings. After a month or so I get the tray back so I can bump the seedlings up to 4" pots, and then back to the greenhouse the seedlings go. We started the first tray of the season a couple of days ago, and it has a mix of sweet peppers, hot peppers, and cold-tolerant tomatoes. Last year almost 100% of the seeds germinated for him and we were over whelmed with seedlings, so I sowed far fewer this year. If they don't sprout there will still be lots of time to sow again.
 
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Well, my first round of herb seeds are doing well, and actually need to be potted up. 3 Types of basil, oregano, sage and thyme. Had a couple of non-germinators, but have had very good luck with the 1.5" blocker. Got rapid germination on heat mats.

Now into second round with tomatoes (3 types) and some more herbs. They are taking a little longer, as DH changed up the plugs for lights and mats without telling me that if I used the switch, I was turning off the lights AND the heat mats lol. They new batches are catching up now that I know!
 
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