How to Make a Soil Blocker

It’s seed starting season.  Yea!!

You can start seeds in any variety of containers.  People use everything from empty egg shells to the plastic six packs last years plants came in to just about any container laying around.  There comes a point at the beginning of the season when you have a lot of plants going and containers can get scarce.  Imagine if you didn’t have to deal with storing mounds of little plastic pots and just did without containers all together!  Well you can and the answer to your prayers is the soil blocker.  It compresses soil into…well…blocks.

Now you can buy a soil block maker.  They cost about 30 bucks from Johnny’s seeds but what’s the fun in that?   I decided to make my own.
You can too .
It’s not that hard.

Molly: I was skeptical when Mike told me about the soil blocker.  I mean, what holds them together?  I still don’t know but they work like a charm.

Mike: I love them.  It’s so easy to make a trayfull of blocks and get on with planting.  Plus when it comes time to transplant I just drop those babies right in the ground.

Soil Blocker

Building a soil blocker takes a few tools and building know-how but nothing insurmountable.

Lets get started!

Stuff You’re Gonna Need


About 2 feet of pine board 3/4″ thick  x 2″ wide

An 8″ piece of 4×4

About 2 feet of aluminum plate 1/8″ thick x 2 3/8″ wide

12 wood screws

1- 3/8″ carriage bolt  4″ long

1- 3/8″ nut & washer

Clear acrylic or varnish


Drill and bits

Table saw

Thin file

3/8″  tap

Start the Wood Frame

wood sides for soil blocker

Cut the 2″ wide stock into 3 pieces one at 8″ and 2 at 6″.

Cut a 45°angle on one end of each of the 6″ pieces.

Drill a hole in the center of the 8″ piece big enough to let the 3/8″ bolt pass through easily.

Now the Metal Frame Sides

Metal sides for soil blocker

Cut two 9 1/4″ long strips off the aluminum.
You can use the table saw for this.  It won’t harm the blade but go slow and be very carefull.

Drill and countersink two holes for the screws on each end of the pieces.

Mark a 1″ line at 2 5/8″, 4 5/8″ and 6 5/8″ on the long pieces.
Each line is centered on the width which leaves about 5/8″ space on either side.
Use a center punch to make a series of divots along the line.
Drill a series of 3/16″ holes along the line.
Use a file to turn the holes into a rectangular slot.

The Dividers

dividers for soil blocker

Cut three pieces at 2 3/8″ wide off the remaining aluminum.
Notch the ends so that they have tabs sticking out of each side.
The table saw and a file works well for this but again be careful.
The tabs are ~1/8″ deep and 1″ wide.  They should fit loosely into the slots.


Starting assembly of the soil blocker


Continuing assembly of the soil blocker

Screw one of the metal strips to the two wood sides.
The tapered ends should point down and face out.
Turn it all over and stand the dividers up in the slots of the lower metal strip.
You’ll need some bits of wood or another pair of hands to hold them up.
Place the other metal strip on top.  Make sure the tabs are aligned with the slots.
Screw the upper side to the wood sides.

The Plunger

Plunger for soil blocker

Plunger installed in soil blocker

Now we make the plunger from the piece of 4 x 4.
Make sure it fits loosely between the two wood sides.  If not make it so.
Cut one side off so that it is a little less than 2″ wide.  Again we want it to fit loosely inside of the cells of the blocker.
Cut 3 slots in it where the dividers go.  Make the slots wide enough to accommodate the dividers.
2 saw blade thicknesses should do it.
The slots should be about  2 3/4″ tall.
When you’re done the plunger should fit…you guessed it…loosely in the blocker.
Test fit it to make sure everything slides smoothly.

Finish the Assembly

Place the plunger in the blocker and tip it up.
Put the top bar of the frame on top of the plunger and use the hole in it as a guide to drill a hole for the 3/8″ bolt in the plunger.
Don’t go to deep.
Tap the hole in the plunger.

Screw the top bar of the frame into the top of the sides with two screws on each side.

Put the carriage bolt through the hole in the top bar.
Slide on the washer and screw on the nut leaving about an inch of the bolt sticking out.
Screw the bolt into the plunger and tighten the nut against it.
Slide the plunger up and down.
Is it working?

Clear Coat

clear coat on soil blocker

Take it apart and spray all the wood parts with a couple layers of the clear coat of your choice,
Once it’s good and dry put everything back together.

Use It

boc choi

The boc choi in the picture was planted last fall in a cold frame.  I just pulled it out of the ground and the block is still pretty much intact.  Pretty cool.

Now that you’ve built this contraption.  How do you use it?
It’s easy but you need a few supplies:

1. Moist potting soil / seed starting mix.  Don’t use garden soil.  Get the stuff in a bag.  Put it in a plastic bin and add water till it holds together in a ball when you squeeze it in your hand.

2. A shallow container.  I use a kitty litter pan.

3. A waterproof tray.  Something to hold the blocks in.  You want it to be waterproof so you can water the blocks from the bottom.

4. A spatula.  Good for moving the blocks around in the tray.

5. A pencil.  Works well for making holes in the blocks for seeds.

Making Blocks

Put some soil in the pan.  Make a mound about 1 1/2 times the height of the blocker cells.  It needs to be deep enough that it will compress as the blocker is pressed down but not so deep that the blocker can’t hit bottom.

Press the blocker into the soil and push down firmly all the way to the bottom.  Twist back and forth a little.

Take the blocker out and put it in the tray.  Press the plunger down as you pull the blocker up leaving the blocks behind in the tray.


You may find that you need to periodically clean the blocker as you are using it if it gets hard to work the plunger.

Now get out there and start planting!


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