How To Make Soil Blocks for Seed Starting

Why, and how, we use a soil blocker to start our seeds

[captionpix imgsrc=”” captiontext=”A soil blocker can make quick work of seed starting.” imgtitle=”soil blocker”]


In the beginning there was the seed starter tray, and it was good. But that was then and this is now. About three years ago we started using soil block makers, more commonly called soil blockers. I was reading Eliot Colemans book, Four-Season Harvest, and he mentioned soil blockers. Liking what I read I decided to give them a try so I bought the mini-blocker and the four hole, two-inch soil blocker. And it was good.

Growing your own food is a wonderful thing but if you are starting from seeds, as we do, there’s always a mess of broken seed trays, plastic cups, and battered 8-ounce yogurt containers littering up the potting bench. I had an almost great system of using 6-ounce plastic party cups in which I used a heated nail to poke draining holes but the cups would split when removing the seedlings. This meant a trip back to the dollar store for every year for new cups. I’ve found that using soil blocks is much more cost effective.

What to I love about soil blocks? Well in a few hours I can make up about ten trays of blocks, have them seeded and labeled. It’s also a pleasure to plant the seedlings as all you do is pick a block up and set it a hole in the prepared garden bed. No muss, no fuss, no busted up seed starter trays flying around the yard with happy, yapping dogs hot on their heels.

Soil blocks can give the seedling roots an advantage because you are making a seed starting mixture with nutrient amendments to turn into soil blocks. This help the seedlings get off to a better start, but you really don’t need to add anything to the mixture at all. The big advantage is the seedlings don’t get root bound in a plastic cup or seed tray. We’ve all seen it before. There’s and argument with the seedling while getting it out of the tray, the tray breaks or the seedling breaks and then the tender roots of the seeding are wrapped around in circles following the contour of the little hole.

[captionpix imgsrc=”” captiontext=”Soil blocks are one of the ways we start our seedlings.” imgtitle=”soil blocker”]

When you plant this the roots need to straighten out and start growing into the surrounding garden bed. With soil blocks the root is “air trimmed” meaning the roots stop growing when they sense the edge of the block. This may seem like a drawback because the root system is less developed. This has not been our experience at all if you time your seed starting correctly. Still, the soil blocks are forgiving and if you do start too soon the seedlings wait patiently for your attention until you can plant them.

Another advantage with this method is how you water the seedlings. With soil blocks you water from the bottom up by filling the bottom of the tray with water. The blocks absorb the water and bring it through osmosis to the seedling. It’s really easy to see if the tray needs water and the soil blocks hold moisture very well.

Like I said up front we bought two sizes of soil blockers, the mini-20 and the four hole. In retrospect I would not have bought the mini-20 as it’s sitting on the shelf gathering dust. I plant directly into the larger allowing me to avoid replanting and making more blocks.

You’ll see the images above I’m using seed trays. I’ve since found a new, more durable tray you’ll see in the following video. It’s called a fish tub it’s what fish filets are shipped to restaurants and grocery stores. You can most likely score some of these if you ask around.

Here’s a video so you can see how we make soil blocks. Grab cup of tea and have a peak!

Here is Eliot Coleman’s recipe for mix. We modified this for our use by eliminating the bucket of soil, the base fertilzer, and using three buckets of compost. To save you the math, 10 quarts is 2.5 gallons.

From the book:

A standard 10-quart bucket is the unit of measurement for the bulk ingredients. A standard cup measure is used for the supplementary ingredients. This recipe makes approximately 2 bushels of mix. Follow the steps in the order given.

3 buckets brown peat
1/2 cup lime. Mix.
2 buckets coarse sand or perlite
3 cups base fertilizer. Mix.
1 bucket soil
2 buckets compost
Mix all ingredients together thoroughly.
The lime is combined with the peat because that is the most acidic ingredient. Then the sand or perlite is added. The base fertilizer is mixed in next. By incorporating the dry supplemental ingredients with the peat in this manner, they will be distributed as uniformly as possible throughout the medium. Next add the soil and compost, and mix completely a final time.

Products mentioned in this post and other stuff we use at Clean Slate Farm can be found here:

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  • reply Your sister-in-law Pat ,

    You should go on TV with this, David! Time Warner Cable News could put you on the air before spring. Just a thought….

    Love the comment about ‘happy yapping dogs hot on their heels….’

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