DIY Compressed Soil Block Maker

One of the things you see a lot in the garden center of the hardware store are little “seed starting kits” that come with disks of expanding peat moss and little customized plastic trays. These are charming, and hold lots of promise for the imaginative beginning gardener, but there’s a reason why gardening books don’t write “Step One: Buy a billion pre-made peat moss seed starting kits.” The obvious reason is that they are expensive! Right now Amazon has a 50-plant starter kit made by Jiffy for just under $11. That’s $0.22 per seedling. That doesn’t sound like a lot, but to put it in perspective, the Handyman and I are starting a little under 300 seedlings inside just for Round One. That’s $66.00! For dirt! I just think that’s ridiculous. The kits are a great thing for children, or people who are starting one or two plants, but for anyone who is beginning a serious garden it just doesn’t make financial sense.

The less obvious reason, thanks in part to the creative photography and marketing departments that design the packaging, is that they actually make more work for you in that they are so small you will be forced to transplant the seedlings at least once before you can put them in the ground. I know the photos on the box show big healthy tomato plants, but those are not going to happen if you keep seedlings in a 1″ x 1″ peat disk.


Transplanting opens up the opportunity to damage delicate root structures. And where are you going to put the seedlings? Well, Jiffy conveniently also sells 3” peat pots for $22 per hundred. Ok, so now my cost is $0.44 per seedling, or $112 total, PLUS the cost of potting soil to fill the peat pots. I’m also out the time it takes to transplant 300 seedlings into peat pots. And don’t believe the line they try to feed you about the peat pots being planted directly in the soil and decomposing. When tilling my soil for my perennial garden last year I found peat pots, IN TACT, from my home’s previous owner. That makes them at least three years old.

Brett Markham, author of The Mini-Farming Bible, recommends using a soil-block method to plant seeds directly into a compressed block of seed starting medium that is large enough to get them all the way through to transplanting. You can buy pre-made blocks of this seed starting medium, or even buy soil block makers, but the Handyman is around, so why should I buy what he can make?

So, instead of spending $112 on dirt, we decided to make homemade soil blocks.

Now, seeds are pretty amazing. Contained within the seed are all the nutrients the plant needs for the first couple of weeks of life. There is no need to buy fertilized potting soil. In fact, delicate seedlings are more likely to be burned by the excess nutrients than they are to be helped. The seed provides the nutrients needed to germinate and push up the first set of leaves, known as cotyledons. Have you ever split a peanut in half? That little nub that you can see on one of the halves is the beginning of a set of cotyledons! Then, those primary leaves can convert light energy into chemical energy by performing photosynthesis, which provides another boost of energy. In fact, it isn’t for the first few weeks that seedlings even need additional nutrients. What they need is good light, a microbe and germ-free environment, and plenty of fluffy soil to let them establish strong roots.

For these reasons, we’ve decided to start our seeds in medium made from coconut hulls, and supplement with an organic fertilizer and compost after a few weeks. For just under $3 we were able to get a brick of organic seed-starting medium that made 36 of our homemade blocks. That’s $0.08 a piece with no need to transplant before they go directly in the ground! Time AND money saved!

A soil block maker is essentially a thingamajig that holds the coconut hulls in place with a plunger to press it into a compact shape. It is possible to buy a soil block maker for around $20-30, but given our decision to buy as little as possible, the Handyman figured he could make one using scraps from the workshop. He found a fantastic YouTube video from Homesteadonomics with directions on making a PVC pipe soil block maker and set to work.

(Now, please please please don’t take this list down to the hardware store and buy what you don’t have. If you have 6″ bolts, use those. Wrong size PVC pipe? Who cares? I won’t tell the plants if you don’t. Just use what you have laying around.)

Materials and Tools:

  • 2″ PVC pipe scraps about 3′ long
  • 2 1/4″ hole saw
  • scrap 1×4 (3/4″ thickness) pressure treated lumber
  • 8″ carriage bolts cut to size
  • nut to fit the carriage bolt
  • plastic (we used the lid of an old 5 gallon bucket)
  • wood screws
From left to right: Two circles of wood cut from 3/4″ thick pressure treated lumber, carriage bolt, appropriate nut, plastic disk cut from old paint bucket lid, 6″ section of 2″ PVC pipe, drill, drywall screws, and a hole saw to cut the disks (this should be adjusted to fit tightly within the PVC, so if you get a different size pipe make sure you adjust the size of the hole saw).

Please check out my post on starting seeds inside to get a good look at this soil block maker in action. It really is brilliant in its simplicity. It forms perfect cylinders of seed starting medium, complete with a little indent in the top for the seeds to go.

Assembly is so easy. Just thread the bolt through both wood disks, use one wood disk to make a handle for the plunger and screw the other one into the top of the PVC pipe to act as a stop. The plastic disk gets attached to the bottom of the bolt with nuts so that it goes up and down with the plunger. The bottom bolt (identified in the picture on the right) is what makes the indent for the seeds.

We’re starting our seeds today, so check back in for updates later.



6 thoughts on “DIY Compressed Soil Block Maker

  1. Cool but I have to adjust for the north and when I start my seedlings they have to be indoor under artificial lights because its just too cold outside. We even get snow in May. I have my starter plants under artificial light and space is limited. So I start mine in a good seed starting soil in a small pack tray with each space about the same size as the small peat pots. But my plastic tray just has to be flipped over and the plant with soil comes out as a unit easy to transplant in later spring when the weather is nice enough to have plants outdoors in my small greenhouse. I don’t like this little peat pellets for exactly the reasons you describe. I envy you your warmer climate and big pots.


  2. I love the idea of making your own. I purchased a soil block maker a few years ago and it was quite expensive. I have had a problem with the soil falling apart in the soil blocks after the seedlings have been growing for a while. It wouldn’t all of the time, but it would occasionally. I am guessing I am doing something wrong. I hope it works out for you.


    1. I definitely noticed that the moisture content has to be just right or they will crumble. As we were working with the mix we would just spritz it with a little water if it started being rebellious, and that brought it right back in line. I would try again, especially if you already invested in the maker, and try using a bit more water. Let me know how it goes.


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