Wednesday, March 16, 2011

Making Soil Blocks

A couple of years ago I started using soil blocks. They have a real learning curve to them. At the start figuring out how to make the block stick together right was hard. I finally started making the soil wet enough. Basically if you can't pick up a handful of mix and squeeze out a little water, it is too dry. I figured out that I should check to make sure the blocks formed well by pushing up with my hand on the bottom. Occasionally one doesn't have enough soil and it would fall apart. Instead now I find that wayward block and manually push in more soil. I've gotten much faster at it.

I also figured out how to water them easily. Most of the recommendation say use a spray bottle. You must be kidding. My hand would get so tired using a spray bottle. It would take forever and promote fungal diseases. Instead I made the system above. The bottom tray is just a flat, with no holes. Inside I put a mesh flat (the ones you get when you buy plants at a nursery). When I needed more of these mesh flats, I asked my friends for some. I now have a stack bigger than I need (thanks Noa!).

The blocks can't stay seated well on them. So on top of that I put screening. This keeps all the blocks flat. I can pick up the flat with holes in it and move it to a flat filled with water and set it there until the blocks are soaked through. Then I move it back to its own holeless flat again. Easy and fast. I think one addition would help even more. If I raised the mesh flat off of the holeless flat so there was some more airflow underneath the blocks, there would be better air pruning of the roots. Now occasionally the roots grow through the screening and run along the bottom for a short bit.

I do not use water straight from the tap. I let the water sit a day (like you would for your fish). This removes all the chlorine from the water. I think the plants grow better that way. Plants really hate tap water. Too many chemicals in it. It amazes me that we survive drinking it.

A soil blocker

Some people hate soil blocks and some love them. Their disadvantage is mainly the learning curve. Until you figure it out, the blocks can fall apart. Mine don't anymore (as long as I use tongs if I want to move them early on). Also it takes longer to plant up. I don't think in the long run they take longer since planting is much faster. I find it really hard to get transplants out of the plastic 6-packs. These I just plop in. Also there is no pot clean up at the end of the season.

One of the main advantages is the blocks don't get root bound they are air pruned. Plants can't grow after they become root bound unless you break up the root which severely shocks the plant. Though I do have issues occasionally when I put the blocks too close together and the roots from one grow into another block. I knife solves that problem easily enough. The other advantage is that there is no root disturbance when the blocks are planted. As long as they have been hardened off appropriately, they have no transplant shock.

And there are no little plastic pots to float around the garden all year long. Don't tell me you pick up all your pots when you should. I don't want to hear it. Mine tend to end up in a pile in the corner of the garden and then the wind blows them around. I also don't have to clean out the dirty pots and six packs. Have you ever tried to clean out a six pack? The brush doesn't really fit into them and they are so hard to clean out. I confess to using the dishwasher on occasion. But no more as I don't use them anymore. Ha!

Size does matter! Personally I love the 1 1/2" block. It is my favorite. Most go for the 2" blocker with the microblocker that fits right in to the 2" one. I love the idea of the latter system. Seed one seed in the small blocks. When they come up move them to a 2" blocks. But in reality I don't use it. The 2" blocks are too big for most of my transplants. I often transplant at 3 weeks for Asian greens and lettuce. And 3-4 weeks for other brassicas. The 1 1/2" is large enough to support that and fits 72 blocks in a flat. 2" blocks only fit half that number. The other major transplants that I do are my tomatoes and peppers. I prefer to start with a 1 1/2" block and transplant them into tall but thin newspaper pots. I think I might use the 2" blocker this year for the peppers though. I'm growing over 40 of them and the newspaper pots take way too long to make. So once again it might get use.

So how many of you all use soil blocks or have tried them? It is a big up front investment. I used the money my MIL gave me for my birthday one year as otherwise I wouldn't have tried them.


  1. I love soil blocks too. It does take a while to get a feel for the soil mix and moisture, kind of like making muffins. I use mini blocks and the 2" blocks for many things. I do use the 1 1/2" blocks for quick transplants like you do. I have used the big 4" block maker for tomatoes, but don't do that now. The 2" blocks do just fine and if I'm going to hold them longer have plenty of old pots around I can pot up to. I really like germinating with the mini blocks. I can fit a lot more plants on my heat pad that way.

  2. Very interesting. How long do your tomatoes stay in the blocks before you pot them up? I've been using peat 6 packs for my quick transplants, but the soil blocks would be a nice thing too. The expense is the biggest thing holding me back.

  3. I bought my soil block maker back in the early 80's from Johnny's. I tried it a couple times and just never got the hang of it...but you have given me hope...I'm going to go down in the basement and dig it out and start all over again with a better attitude!

  4. This is our first year trying to use soil blocks. Our tools were on back order and arrived just a few days back. We are going to try it out this weekend

  5. I love my soil block makers...I use the 2" blocks for larger seeds or plants that will remain in the greenhouse for a while...the mini block maker for small seeds that I just want to germinate quickly and then plop into the garden beds...thanks for the advice on the soil mix for the mini block maker...screening out any larger chunks and pushing harder made the difference....

  6. I still cut up milk cartons or save plastic tubs from various food items and jab holes in the bottoms for drainage. I haven't seen a root bound problem.

  7. Great post on soil blocks. I love my 2-inch soil blocker. I don’t water with a spray bottle either, that would take forever and cause some joint pain. I use a turkey baster to water each block, but I love your watering system much better. I only have one mesh flat right now and will try to find more.

  8. I have to agree, Daphne, getting the soil just right is where you can go wrong- the first thing I tried was Coleman's recipe, which works really well. When I'm out of the ingredients to make it I use Black Gold Coco mix (the coco is the important part). I take that and sift it getting the larger perlite out and add what ever fertilizers I'm using at that time- usually greensand, powdered phos, etc. I don't add vermiculite to the mix, as some do, because once the particles are squished (in the soil block maker) that's it- its done and they don't puff back up to hold water. For a quick mix I just sift the BGcoco and add sifter compost and I've never had a problem with the blocks falling apart. I don't use them exclusively, but I probably would if I always had a supply of soil mix! I love them!

  9. Alan, the mini block does have that advantage. It will be useful for my peppers too. I'm going to be growing a lot of them and I won't quite have the room yet under the lights. The problem though is that I will need twice the light space once they get potted up to the 2" ones.

    The Mom, usually about three weeks. I don't grow big tomato transplants. I'm strange that way. I think tomatoes do best at 4-5 weeks not 8 weeks. So at 3 weeks they get potted up and not long after once their roots fill out the newspaper pot, they get transplanted.

    Lynda, it really is hard to learn. If you do try again, remember that the soil really has to be wetter than you think. And make sure each block is well compressed.

    Brindavan, good luck

    Deb, I'm glad it is working better for you.

    Karen Anne, if you don't have to hold your plants too long, there shouldn't be a root bound problem. But if you have ever bought plants from a nursery, they are almost always root bound. All you need to do is wait a bit too long and those roots will wind around the bottom.

    GrafixMuse, good luck. I'm sure some places sell them too, but I haven't seen any.

    Tessa, I love them too. If they were popular enough the garden centers would sell soil mix for the blocks. But I think with the costly entry fee and the learning curve, they won't get popular.

  10. I have a video about how to make them at
    I like that I can start even low germination seeds and waste nothing. Blockks go into garden soil. Also, I water with a turkey baster.

  11. Esther, I saw you use a toothpick to pick up seeds. I used a sharpened pencil. Well I do if the seeds are small. I use my fingers for the larger ones as I don't have an issue getting just one of those. I also didn't say above, but cover my seeds with vermiculite and then sprinkle the tops with cinnamon (reduces fungal diseases).

  12. I have always wanted to try making soil block but never have. Thanks for sharing your thoughts on them, now I will have a better idea on how to do it right if I try making my own.

  13. Interesting! I had never heard of soil blocks before, and it does look like a lot work. Where do you buy the soil for the mix?

  14. This is my first year of 'real gardening' as an adult. Previously we were apartment dwellers.

    My husband bought me the 3/4 and 2" blockers for Christmas. Honestly, I'm still getting the hang of it, even though most of my plants are already seeded. I think it's worth it not to have to deal with all that plastic, but you are right about the learning curve.

  15. All this talk about the advantage of soil blocks and nobody remembered to say that all that compressed soil provides the nutrients a plant needs while waiting to go into the garden! Don't 6 packs cells often require a fertilizer supplement, because there's simply not enough soil to supply the nutrients. Soil blocks seem to solve that problem well enough.

  16. I have been on the verge of investing in a soil block maker for many years now and have always talked myself out of it. The helpful advice and information that you and others regularly share about them, is getting me more interested again and I am likely going to ask "Santa" for a block maker for Christmas this year - so I am set for using it for next spring's seed starting season. This year, I am sticking to my tried and true methods and just reading about the soil block makers to learn as much as I can before I make that leap. Appreciate the useful tip about the screening to make bottom watering easier.

  17. Mr H, Maybe some day you will try them.

    RandomGardener, I bought the mix (Vermont compost company's For Vee potting soil) through the bulk buy of the Northeast Organic Farmer's Association. Unless you live in the Northeast you probably can't get any of that particular one. Most people make their mix or use something like Promix that you can get anywhere. I don't know how well promix stick together personally but others have had success with it.

    tanna, I so hated dealing with all the plastic pots. Especially the cleaning.

    Jody, True the mixes that people make or the one I use have a lot of nutrients in them. They aren't just plain peat mixes. And the amount of soil in a block is rather large for its size so usually I don't have to fertilize. I've found for the 1 1/2" blocks that they are fine for four weeks with no fertilization at all. I haven't had enough experience with the 2" blocks to make that statement. But I'm guessing they would go for 6-8 weeks.

    kitsapFG, I read about them for a long time before I took the plunge and bought them. They are a significant investment. Especially if you have three different sizes like I do.

  18. I've been intrigued by the whole soil block thing ever since I began gardening. Admittedly, that was only about a year and a half ago, but still. However, I figured I should get the basics down before trying to figure out the advanced stuff. I'm planning on saving up some money though and try this method out next year.

    - Cloud @ Metro Gardener

  19. You're right about the learning curve! I tried soil blocks last year, but didn't have much success. The first sets of blocks disintegrated when I tried to move them. Later sets I tried to compress more for stability, but the plants started in those blocks were stunted. My best guess (based on online research) is that they were *too* compressed. This year I added more soil to my mix and used more water. So far the blocks are holding together with less compression. I'm still waiting to see how the plants do in the long run. I have my fingers crossed - I'd love to do away with the pots altogether!

  20. Daphne, I will have to try the cinnamon. Damping off (fungus) is the only issue I have and it's a bigger risk with the things like onions and lettuce that don't want bottom heat.
    Some other comments that may help others:
    Seedlings never need fertilizer until they have their first true leaves.
    I use Pro-Mix; you can buy a large bale at Agway and it will last a long time. I have also used BMX mix but I needed to pull out a lot more sticks. These do not have nutrients added.
    Johnny's videos for soil blocks showed someone plunging them into soil and coming out with perfect blocks. That may be possible with perfect soil but not realistic from my experience.
    If I were buying only one set it would be the 2" size. I've been lazy and had 10" tomato plants growing in them. When I'm not lazy, I pot up my tomato plants to peat pots or sterilized, re-used plastic ones.
    The little ones dry out quickly.

  21. I love my soil blocker. In the past I used Fort Vee and the organic stuff from Lowe's, but this year I also have ProMix and Master Gardener (or something like that), I have yet to find a mix that doesn't work.

    I still use flats for some seedlings, but the blocks are all I will ever use for things that need to be potted up. Then I like to use the cow pots (made from manure), as they can go right in the soil and do some good. More money but the tomatoes seem to like them.

  22. Hi! Have you ever paid attention, have your writting skills improved recently?

  23. Daphnie -
    I use the exact same soil blockmaker. I think that the deep dowel pin inserts are probably the best investment I made when I purchased my soil block maker. It's fun to see other gardeners using the same techniques!

  24. I've been using the blocks for 3 years now and love them. There is a bit of a learning curve but you get the hang of it pretty quickly. Its a little more labor but filling a bunch of pots takes time too.

    You said above:
    "I think one addition would help even more. If I raised the mesh flat off of the holeless flat so there was some more airflow underneath the blocks, there would be better air pruning of the roots."

    I'm not sure how many seedlings you have but you could use the large plastic light diffusers (like the ones they put in ceilings over fluorescent lights) to raise your trays a 1/4 inch or so. I use these for my trays and have a similar watering system to yours. Just go to lowes and check the ceiling tile area. It is a roughly 4'x2' grid panel for around $10. I tried to find the exact one on the lowes site but can't tell which one is the grid from the pictures online. You could also build some risers with cheap wood (2"x2"s)and some hardware cloth.

    I haven't used the extra screening in the bottom but think that is a great suggestion so I'm gonna try it moving forward! I have the diamond bottom trays so the gaps are even larger.

    Happy growing season!