How to Make Soil Blocks for Seed Starting

Learn how to make soil blocks for seed starting. Soil blocks are easy to use, cheaper than peat pellets, and better for the seeds because their roots have room to expand and thus are easier to transplant. Below is my tutorial and recipe for creating soil blocks at home. At the bottom of the post is a bunch of pictures of my soil block making adventures (including what went wrong and how I fixed it).

I haven’t made many suggestions on this website for gardening books. You wanna know why? I have read tons and tons of them and usually find them lacking. In fact, I’ve only made ONE gardening book recommendation on this website so far, which was in my article on what to plant to encourage beneficial insects, and I mention Amy Stross’ book The Suburban Micro-Farm: Modern Solutions for Busy People. It’s a great gardening book for beginners and those that live on small homesteads.

Now, however, I have another great gardening book to suggest for you: The New Organic Grower: A Master’s Manual of Tools and Techniques for the Home and Market Gardener by Eliot Coleman. I’ll tell you right away: this is not the best book for beginner gardeners.

However, if you’ve been gardening for a while and you’re looking for ways to boost your garden yields and your gardening knowledge, I highly recommend this book! It has been expanding my gardening skills over the last few months. 

One new thing that Eliot Coleman got me thinking about is using soil blocks for seed starting. In the past, I have exclusively used peat pellets. There’s nothing wrong with using peat pellets, especially for small-scale gardening.

However, I’ve been getting more serious about my seed starting, and, between my vegetable seeds and my bajillion flower seeds, I’m starting at least 300 seeds a year now (confession: this might actually end up closer to 400…).

That was getting a bit costly with the peat pellets, so I was on the hunt for a new seed starting concept. And then Eliot Coleman’s The New Organic Grower book had an entire chapter on soil blocks. Huzzah!

Are you new to gardening? You can learn more about seed starting in my articles here:

• Homemade Seed Starting Soil Mix (I use this soil recipe for seedling transplants when they’ve grown too big for the seed starting blocks/pellets)
• How to Start Seeds Inside
• Common Seed Starting Problems and Solutions

Why I’m Switching to Soil Blocks

According to Eliot Coleman, soil blocks are easy to use, more effective, and less expensive than the other options. A soil block is simply a block made out of lightly compressed potting soil. 

A soil block is the perfect seed starter because:

• The roots don’t circle and get root bound when they get to the edge of the soil block (which they do in other types of seed starting containers).
• The roots become quickly established when you transplant them to bigger pots, causing quicker growth and better health.
• You can avoid the expense of trays and containers and also squeeze more of them together in an area to save space.

I’m looking forward to saving money with soil blocks, too. I spend $40.00 on 200 peat pellets each year. And again, I’m starting at least 300-ish plants this year, so I probably would spend $80.00 on peat pellets, with a few leftover for failed germination and saving for the next year.

Speaking of saving money, the best place I’ve found to buy good-quality seeds online is True Leaf Market. By using quality seeds and your own soil blocks gardening is more affordable than ever.

With soil blocks, while they do use a lot of soil, I already own most of these ingredients for my homemade seed starting soil mix that I use for the transplants when they outgrow peat pellets.

I did some math below to show the prices of the soil block ingredients vs. peat pellets:

Soil Block Ingredients I purchased:

• 20 lbs perlite: $27.00
• 2 cubic feet compost: $11.00 (free if you get it from your garden)
• 2 cubic feet garden/top soil: $6.00
• 8 lbs Espoma Garden Tone fertilizer: $11.00
• 6 lbs Organic Garden Lime: $5.00
• 3 cubic feet peat moss: $12.00

Total Cost: $72.00

Compare this price to the total for 400 peat pellets: $80.00

Important Soil Block Note: the amounts mentioned above are WAY more ingredients than the 300 seed starters blocks I started with my recipe below. I seriously barely made a dent in these products! This just happened to be the smallest sizes of the products that I could find. You might be able to find these ingredients in smaller bags, which would make it even cheaper for you.

The most expensive part for using soil blocks was actually the soil block maker itself. I had a hard time finding them, especially the size that I wanted. Eliot Coleman explains that there are different size soil block forms: 3/4-inch (aka 2 centimeter or mini-blocker), 1.5-inch (aka 4 centimeter), 2-inch (aka 5 centimeter), 3-inch (7.5 cm), and 4-inch (10 cm). 

He suggests getting a 3 or 4 inch soil block maker, because you can use it for seed starting for all types of plants; you don’t have to keep transplanting the plants to larger-size soil blocks as they keep growing; and it can save you money on the soil recipe parts.

His book shows pictures of all sorts of sizes of soil block makers, and I would have LOVED to find the 4×3 soil block maker, so I could have made 12 soil blocks with one push.

However, I had the hardest time finding larger-sized soil block forms, and finally settled on Johnny’s Selected Seeds’ 2 inch soil block form for $37.00. That’s more than I like to spend on something, but it seems to be a durable device, and it should last me for many years if I take good care of it. So it’s a one-time expense (hopefully) that I shouldn’t have to make again.

Soil Block Soil Mix Recipe

My recipe is based Eliot Coleman’s recipe with a few small changes, mainly to the fertilizer additions. It was very difficult for me to find collodial phosphate and greensand in a local gardening supply store. I heard from another local farmer that there is a place that sells them about an hour away from me, but that’s a bit far to travel for two items. 

In the future, I might try to stock up on the rare garden stuff at this far-away store, but for now, I used what I could find. I’ll give you a few options, in case you live in a small town like me.

I also found it brain-boggling in Eliot Coleman’s recipe that he switches between the terms ‘buckets’ and ‘cup’ for measuring the ingredients. And then he says ‘bucket’ equals ’10-quarts’ and it was driving me crazy (especially since standard buckets are 5 gallons…gah! My brain hurts). So I figured out the recipe using a standard 5 gallon bucket and also include a more ‘normal’ consistent measurement so you can make your soil block mix using whatever buckets you have around.

Term: Bucket = 5 gallons (aka 20 quarts)

This recipe made 315 seed starting blocks (with a little bit extra that I composted for future use)

Ingredients:

• 3/4 bucket (aka 15 quarts) Peat Moss 
• 1/2 bucket (aka 10 quarts) Perlite
• 1/2 bucket (aka 10 quarts) Compost
• 1/4 bucket (aka 5 quarts) Top Soil
• 1/4 cup Garden Lime
• 1.5 cups Organic Fertilizer (I used Espoma Organic Garden Tone. You could also use equal parts: blood meal, collodial phosphate, and greensand OR any organic all-purpose fertilizer OR E.B. Stone Organic Sure Start Fertilizer)
• Water (if you use city water, try to use filtered city water. I used rain water)
• Equipment needed: soil block maker, a deep tray/small tub, seed trays or something to hold the soil blocks, and wheelbarrow/large tub

Directions: 

1. Mix the soil components in a wheelbarrow or large tub.
2. Move a portion of the soil mix to a deep tray or smaller tub (this is simply to make it easier to mix and also easier to create the soil blocks, see notes below for more info).
3. To the portion of soil mix, add approximately 1 part water per 3 parts soil mix.
4. This is tricky to figure out perfectly (and hard to write out instead of show you in person). Basically, start with 1 part water to 3 parts soil mix and mix it thoroughly. You want to get the consistency of oatmeal, peanut butter, or brownie mix. It’s hard to find the right descriptive word, but we’re trying to end with a soil that’s not too wet, but wet enough to make the soil block forms and hold together. So after adding the original water, mix it and add just small amount of additional water at a time until you get the right texture.
5. Have a 5 gallon bucket of water next to you as you work. Before starting, dip the soil block maker in the water.
6. Mound up some of the soil mix in the tray/small tub. Plunge the soil block maker in that soil and press down firmly. Consider twisting it a bit to get it packed in tight. The corners of the edge blocks can be a little difficult to get enough soil in them, so peek at the bottom and jab it in the soil again with pressure on those areas if it’s not looking as perfect as possible.
7. Level the bottom of the soil block maker (I used my hands, though a garden trowel or an old kitchen knife would work, too).
8. Then move to an old seed tray or whatever you are using to hold the soil blocks. Squeeze the release on the soil block maker by pushing down on the handle and lifting the blocker.
9. Dip the soil block maker in the bucket of water between every 1-3 uses (see notes). This keeps the blocks from sticking and also prevents a mess.
10. The blocks should be firm. If the blocks crumble, you need to add more water to the mix. If the blocks slide out easily and fail to hold their shape, then you need to add more dry mix.
11. The blocks have little indents in the centers, which is perfect for placing your seeds. You do not have to cover the indents with soil when you put the seed in the indent.

Notes:

**Eliot Coleman suggests putting the soil blocks in a 3-sided flat/tray. However, I have plenty of old seed trays lying around, so that’s what I am going to use. 

**Tip: do NOT wet all of your soil block soil mix at the beginning because you’ll probably need to add dry mix as you work through creating the soil blocks. This is why I suggest working with small amounts in Step #2.

**Make sure to firmly press down the soil block maker in order to get the good soil blocks. In my first few attempts, my blocks kept falling apart and I got super frustrated…until I realized that (duh) you still have to press down to get the soil to compact in the form. See one of the pictures (below) to see what it looked like in my first batch and second batch.

**Eliot Coleman suggests dipping the soil block maker in water between each use. However, I found that was making my soil mix too wet. So I started dipping it in a bucket of water every 2-3 uses and that worked great. I knew it was time to rinse the soil block maker when the blocks would stick to the inside. I suggest playing around with it and finding what works best for you.

**Even though I could only make 4 blocks at a time, once I got the hang of the soil block maker, I made 315 soil blocks pretty quickly and easily. So this doesn’t really take that much time.

**Feel free to halve the recipe if you don’t need that many soil blocks. However, they stay useable for at least 3 weeks after making them, so if you think you’ll need 300-ish seed starting blocks throughout the season, I suggest making them all at once.

**Sow only one seed per block unless you are worried about low germination rates with an old packet of seeds (learn more about testing old seeds for viability here).

So far, I’ve started some flowers from seed in the blocks and it’s going really well! I’m spritzing water on the tops of the soil blocks right now and once they develop their first True Leaves, I’ll start pouring water in the bottom of the trays to soak up through the blocks. This helps prevent damping off (learn more about damping off here).

Since I’ve been taking an Herbal Academy Course I’ve also been excited to start a new batch of soil blocks to grow lots of herbs.

I hope my info inspired you and that you learned a lot about how to make soil blocks. Please add comments to this post if you have questions!

Below are some more pictures of my soil block adventures.

More Gardening Tips:

**Check out the Vegetable Varieties I am growing this year!

**How to Start Seeds Indoors

**The Insanity of Spring: A Gardener’s Reflection

**How to Make Seed Starting Soil

Pictures of My Soil Block Adventures: