Starting Seeds with Soil Blocks

New Methods

A few years ago I was inspired to change up my seed starting system to include soil blocking. I now use it exclusively.

If you’re not sure what soil blocking is, I’ll walk you through the whole process! Soil blocking requires taking a wet growing 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).

After lots of experimenting with growing medium (I’ve mixed my own, I’ve purchased all sorts of seed starting mix) I’ve settled on Pro-mix MP Mycorrhizae Organik. I purchase large bales at Southside Garden Supply each spring.

If you’re interested in trying to mix your own starting mix, here’s a recipe from Lisa Mason Ziegler. She’s author of Cool Flowers (a great book about maximizing your cool shoulder seasons for planting early in the spring or late in the fall - I’m still trying to perfect this method in a snowy climate, and honestly still sort of flailing):

Recipe

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 farm or garden 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.

If you’re using Pro-mix MP Mycorrhizae Organik or another pre-made mix, just mix a set amount of soil in a tub and add water until it’s a very wet mud.

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 seedling tray bottoms with no holes. I reuse these every year for 3-5 years! Folks also use lunch trays, plates, left over styrafoam 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!