Starting Seeds with Soil Blocks

New Methods

Last year I was inspired to change up my seed starting system to include soil blocking. If you’re not sure what this is, please read on! Soil blocking requires taking a wet grow medium and using a little blocking press to create perfect stand alone squares in which to sow a seed or transplant. I invested in a 3/4” blocker for germinating slow growers and tiny seeds and a 2” blocker for transplanting into or sowing larger or quick growing seeds. These are available from Johnny’s Seeds (my favorite online planting/growing store).

That first year I soil blocked, I purchased the most natural potting soil for seed starting I could find and was determined to make soil blocking work with that. Because of this oversight I almost threw in the towel! My mix was crumbly and seeding was tedious. This year I opted to mix my own after reading about a super easy recipe in Cool Flowers by Lisa Mason Ziegler (if you love growing flowers, this is a must-read for you). 

Using my custom seed starting medium is so much faster (it holds together better), soaks up water better (the little blocks just swell with each watering and don’t melt like they did with the regular potting soil), and hold their form longer once planted (which will help big time once its time to transplant).


The recipe includes: 

16 C sifted peat or coco fiber (I used our local Fishy Peat mix available at Mill and Feed) 

4 C of sifted compost (I used Susitna Organics humidified compost)

1/4 C greensand (available at Southside Garden Supply - let me put a plug in for this awesome local shop. Thanks to the marijuana industry, this place is loaded with great stuff for the urban set-up)

1/4 rock phosphate (Mill and Feed or Southside Garden Supply)

6-7 C water

How To

Mix all ingredients well in a large tote or bin. One batch makes around 600 mini blocks. Since I’m still just seeding in mini blocks, I’m mixing two batches per week and letting the leftovers sit uncovered until the next seeding. Once I start using my large 2” blocker, I’ll be mixing much more per week as this blocking press uses a lot of soil!

Once your planting medium is all mixed grab your blocker, dip in a dish of water (aids in releasing blocks), firmly press your blocker down into soil medium a few times to really pack it in, scrape off excess, and while holding just above the bottom of your seeding tray depress the plunger until blocks release. It takes a few tries to get the hang of it! Seeds can then be planted in the little depression left my the blocking pin. Get creative about what you use for trays. I use regular seeding tray bottoms with no holes. Folks also use lunch trays, plates, left over styrofoam trays, yogurt lids, etc.

Growing on

To water, less is more. Although you don’t want to desiccate your precious seedlings it’s easy to over water and get disastrous results (like damping off). Be sure to water from the bottom to preserve the delicate soil block structure. They wick up water like crazy. 

Once the 3/4” blocks are ready to transplant, plant directly outdoors or up-pot into a 2” or 4” block. I up-block into a 2” block for most of my starts. The larger seed blockers come with a different blocking pin that creates a square indent that perfectly fits a 3/4” block. Now go grow some epic plants!