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Pros and cons of soil blocks for seed starting  RSS feed

 
Peter Smith
Posts: 83
Location: NEPA
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So, I am making plans for my first semi-commercial farm garden. I hate those silly plastic pots that end up all over, and I am interested in trying soil blocks.
Pros
Hopefully cheaper
Healthier plant roots
No plastic pots
Cons
Finicky soil mix
Fall apart ?
This is what I am finding, and Elliott Coleman makes it look very easy. I have no personal experience, so I'm wondering if anybody has tricks, tips, warnings, endorsements, soil mixes. Or is nobody using these.
Coleman's mix is
3 parts peat
3 parts compost
1 part pearlite
Plus minerals and fertilizer
 
Adam Klaus
author
gardener
Posts: 946
Location: 6200' westen slope of colorado, zone 6
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I have made soil blocks in the past. I went back to little plastic pots. Here's why-

The soil mix does need to be good. I am not one for buying lots of peat moss and such, but I did manage to make a decent on-farm soil block mix using sand, clay, and compost. I dont remember the exact ratios, but it isnt that difficult to get right. It should be more dense and sticky than you would think for potting soil, otherwise it does fall apart.

Thing is, you need a ton of this mix for your soil blocks. The main thing that I was using soil blocks for was tomatoes and peppers, using the 4" blocks. I ultimatley gave up on the soil blocks because if I raised my tomatoes in 50 cell trays, and then transfered to half gallon plastic pots, I could use nice mix in the flats, and then just garden soil in the big pots. This was much easier to deal with.

I never saw better growth in the soil blocks. In fact, I think the half gallon pots grow a better transplant. The plastic trays and pots are reusable for years if you put them stacked in a shed. It is much cheaper using the plastic containers because the mix is so much cheaper.

Just my experience, I still have the soil blockers (2 inch and 4 inch), but I havent used them in years. It works for Elliot, no doubt, but was a disappointment for me. Of course, YMMV.

good luck!
 
John Polk
steward
Posts: 8019
Location: Currently in Lake Stevens, WA. Home in Spokane
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My only experience (at somebody elses' grow shack) was that once you got the soil mixture right (so the pots wouldn't just fall apart), they were so tough that the roots could not penetrate the soil. He ended up with a ton of tiny plants that were root-bound, and none of them ever recovered to become full sized, healthy plants.

As far as the peat is concerned (many people feel that this is not a renewable resource), I have been informed by people living in the peat-bog regions that those bogs are expanding each year. If we (or somebody else) don't 'consume' this product, the peat will overrun millions of acres, making it unsuitable for anything else.

Next, perlite. I hate that shit. It is so light, that every time you water, it floats up. Eventually, almost all of it ends up on the surface, where the wind just blows it away.

I much prefer to use soil flats. Nothing is wasted that way. If a seed doesn't germinate, you only lose the temporary use of 1 square inch of soil. With soil blocks, you need to put 2-3 seeds in each, and select for the healthiest one, clip the rest. One half, to two thirds of your seed is wasted.

 
Dustin Powers
Posts: 42
Location: Washington State
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I didnt love my soil cube until I used them on a wicking watering mat. Cubes stopped falling apart, root growth in its hunt for water was stronger therefore holding the cubes together better, and I just used a mix of my garden soil and some light potting soil.

It was always the watering that broke the top corners off my cubes.
 
Carol Allen
Posts: 6
Location: Oklahoma
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I only use the 3/4 inch and the 2 inch, and I love them. One tomato seed to one 3/4 inch block is almost no waste if it doesn't germinate and you only go to the 2 inch if you have a growing plant, so I don't understand the waste comment. I would use more soil in a pot than I do a block.
 
Jennifer Wadsworth
Posts: 2679
Location: Phoenix, AZ (9b)
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I used the 2" blocks for a couple of seasons and then found the same thing John did - the blocks do not degrade in my climate which is very hot and very dry. I, too, ended up with hard little cubes that stunted plant growth. In fact, I am STILL finding these little cubes in my yard years later. Peat pots don't break down in my climate either - if I should get a plant in a peat pot - I peel off the pot and tear it into tiny pieces and put it into the compost pile.
 
Jen Shrock
pollinator
Posts: 363
Location: NW Pennsylvania Zone 5B bordering on Zone 6
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I live in a temperate, wet climate. I tried them one season (the small ones for starting before potting up) and I had success with them. They made the transition to being potted up well. This year I mixed up seed starter mix and put it into small cell trays and I am not impressed. Many of my plants are having a full on revolt at being potted up. Think that I might go back to the blocks. They are more work up front, but I had a lot more success with getting my plants to the next stage. I haven't tried the bigger blocks. I think the size I was using was 3/4"
 
Weston Ginther
Posts: 63
Location: NW South Dakota - Zone 4b
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Dustin Powers wrote:I didnt love my soil cube until I used them on a wicking watering mat. Cubes stopped falling apart, root growth in its hunt for water was stronger therefore holding the cubes together better, and I just used a mix of my garden soil and some light potting soil.

It was always the watering that broke the top corners off my cubes.


What were you using for a wicking mat under your soil blocks? I've been thinking about making my own out of some unbleached, natural wool fabric. There's a bunch of different synthetic wicking mats (a.ka. capillary mats) out there on the market but I like to use the most natural materials I can. So if anyone has other suggestions (other than newspaper, haha) I'd appreciate it.
 
John Polk
steward
Posts: 8019
Location: Currently in Lake Stevens, WA. Home in Spokane
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I like to use the most natural materials I can. So if anyone has other suggestions (other than newspaper, haha) I'd appreciate it.

Would coco fiber (coir) work?
A waste product, that seems to last quite awhile before it 'returns to the earth'.


 
Karen Walk
Posts: 122
Location: VT, USA Zone 4/5
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I use soil blocks and they work well for me. I use a mix of compost, peat and sand. I don't have much topsoil suitable for starting plants. Just sod and clay. My blocks are a little fragile.

I would not use much clay in a soil block, and if I did, I would not use sand. After all, rammed earth is a compressed mix of sand and clay.

I would like to find an on-site replacement for peat, but haven't had time to experiment yet. In regards to expense, using soil blocks greatly reduces the need to add compost to the soil, so they might use more materials than starter trays, but it is important to look at the complete cost of the system.
 
David Joly
Posts: 4
Location: Saint-Didace, Québec, Canada (Zone 4)
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I've been using soil blocks for 2 years for vegetable seedlings and I like this system. I feel that it is a little more work to start the seedling, but much less work when it is time to transplant seedlings.

I used 10" x 20" plastic trays in which I can put 40 or 44 2-inch soil blocs. I do not need any other plastic cell pak (so less cleaning to do and less stuff to pile somewhere !)

It needs some practice to find a good mix. Many will work, but I usally use a mix of commercial mix inoculated with mycorrhizae, compost and coco coir. I found that coco coir is really helping to maintain the sturdiness of soil blocks, especially for big 4" blocks. The right amount of water in the mix is also critical so the block won't fall apart.

I do not know if seedlings are healthier with soil blocks than with regular trays/pots, but I know that they are very healthy. They are sturdy, easy to manipulate and easy to water (just pour water in the 10x20 trays). I have not seen any difficulty for the roots to grow in the soil blocks.

I tend to use less often 3/4 inch blocks as I feel that it is more work and germination rates are already high in 2" blocks. For tomatoes, I use the longest pin with 2" block and I put the seed in the hole. As the plant (and its main stem) grows, the stem inside the hole seems to make roots and the seedling is quite sturdy.

David
 
Aaron Martz
Posts: 29
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I've had good results from making soil blocks. I also don't like using plastic trays and find after a few years that they break apart and I have a constant inner struggle whether to use them again in damaged state or finally buy new ones.

I have made them with peat and coco peat. Both have worked well, though I personally want to find a local solution because importing those materials just brings up the cost and emissions of what I grow. I have read about making a degraded leaf litter as a peat replacement, but haven't tried this yet.
Here's a similar thread with good suggestions: https://permies.com/t/7049/organic/Soil-Block-Makers-Eco-conscious
 
Gilbert Fritz
Posts: 1279
Location: Denver, CO
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I'm wondering if sod of some type could be put under cover to die off, then used as soil blocks. The root mass ought to hold things together, and eliminate some of the need for exotic ingredients. If nitrogen fixers were included in the sod, that would be a further advantage.

Now I'm thinking; what if in the Fall we laid out several inches of compost, and planted clover or some other such plant in it, along with an annual grass. Then, we would cut the "sod" up into blocks and put them under cover to dry out and die. Come spring, could we rehydrate these and use them as soil blocks?

If a little clover came back, that would not necessarily be a bad thing.
 
Tracy Wandling
steward
Posts: 1618
Location: Cortes Island, British Columbia. Zone: 8ish Lat: 50; Rainfall: 50" ish; sand and rocks; well water
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I really liked using my soil blockers. First time using them this year, and was very pleased with the results. I had to start things inside under lights and heat, so had very little space, and the 3/4" blocks were great for that. Lots of things started in a very small space. I potted up to the 2", and by that time I could spread things out more, as they didn't need the bottom heat after germination. By the time it was time to pot up the tomatoes, I used recycled 6" pots I got at the free store, and could put them outside in my little greenhouse.

I used the soil mix recipe from Eliot Coleman's The New Organic Grower. In that mix he advocates using sharp sand, not perlite. I generally used what I had - not-sharp sand, some used seasoil, compost and peat moss. I added amendments such as rock dust, greensand, lime, and some organic dried seaweed stuff. It worked great. The blocks held to gather well, and everything grew very healthy and strong. Misting is definitely the way to go with the 3/4" blocks, and the first few days of the 2" blocks. But once the roots have infiltrated the blocks, regular light watering worked well; although, I can definitely see the advantages of using some sort of capillary mat to water, as you would not have to be quite as diligent in keeping them watered.

All in all I was very pleased with the results. I think that experimenting with things like worm castings and leaf mould will be in order in the future. Anything that is nutrient rich, holds water, and holds together well should work brilliantly. I'd definitely like to be using only on-site materials as soon as possible. So, hopefully in the spring I'll have everything I need - compost, sand, garden soil, worm castings, leaf mould - and I'll have a go at using different mixes to see what works best.

Oh, how I love experimenting!!
 
Jonathan Rivera
Posts: 29
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I just started using soil blocks last year, and I can say I won't go back to pots. "Potting" up is a breeze, and I save so much more space and time over traditional seed cells and pots. I think others here were having issues because they either mixed clay and/or let their blocks dry out. As long as the blocks stay moist they don't harden at all and can be crushed easily with your hands. Leaf mould, vermicompost, and a bit of wood ash will do the trick for a great mix. You could mix some sand in there to add more aeration if that becomes an issue.

I would avoid Peat moss for a multitude of reasons. My primary concern is it just doesn't absorb and distribute water properly, therefore requiring a host of other ingredients to compensate (perlite, vermiculite, etc). Even with perlite, the Peat blocks I made tended to dry out and harden readily. I switched to coco peat with vermicompost, which worked much better than the Peat moss. The vermicompost held everything together perfectly, but you need to make sure your moisture is right when creating the blocks.

This year I'm experimenting with well rotted pine. After sifted, It's about the same consistency as the "Coco Peat" but free and readily available for me. It's also inoculated with Mycorrhizae and should theoretically contain a better mineral mix. I just started some onions in the 3/4 inch blocks, I'll post an update here and let everyone know how it goes.

Pros:
Free after initial investment
No plastic
Less space (no plastic taking up storage, or cell space)
Less water (if done right the blocks absorb and hold on to water better than plastic pots)
Faster transplanting and potting up
Less transplant shock

Cons:
Higher initial investment
Takes some time to get the consistency and mix right
Won't work with garden soil (clay will turn these into hard rocks)

 
Tj Jefferson
pollinator
Posts: 205
Location: Virginia USDA 7a/b
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An idea for wicking mats, born of necessity: I used cardboard with the edges turned up and stapled. One extra sheet of cardboard inside for more absorbency. What Dustin mentioned above I agree with, the roots are seeking downward. I used 2" blocks and no perlite, just commercial potting soil and a little dirt, and they have held up ok. I didn't read John Polk's advice before buying it, so I will figure out what to do with it. I think I am going to try to Unfortunately can't do a RMH.


Once the plants are bigger, staples come out and the cardboard will be used in a sheet mulch for some of the same plants.
 
Angelika Maier
pollinator
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Location: cool climate, Blue Mountains, Australia
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I grow mostly perennial plants to sell. I start all seeds in these white polyboxes you get at the greengrocer and then use the nasty plastic pots and hope to get back as many as possible. When I ws a kid gardeners used to sell lettuce seedlings in a big block which they cut up with a knife, the seedlings wrapped in newspaper. Unfortunately all degradable pots are too expensive.
 
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