Soil-Block Your Seeds

comments (12) February 19th, 2009

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The soil blocker is constructed so each square has a built-in planting hole.  
1. Packing the wet mixture very tightly into the blocker is the key to non-collapsing soil blocks.
2. Finished blocks, looking a bit like brownies, drop into the waiting tray.
3. Fit the blocks together snugly to prevent their sides from drying out so fast.
4. A seed for every block, and in a few weeks, youll have flourishing plants ready for the garden.
Antiqued by much usage, the authors favorite garden tool is still going strong.
The soil blocker is constructed so each square has a built-in planting hole.  Click To Enlarge

The soil blocker is constructed so each square has a built-in planting hole.  

Photo: Scott Phillips

Back in 1989, while wandering the aisles of the Northwest Flower Show, suddenly I saw it: a fascinating implement with such appeal that I instantly gravitated toward it. After a long conversation with its owner, I purchased one, carefully packed it in my suitcase, and took it home to British Columbia. It was a soil blocker, and since then it has been my constant companion. I use it for all the indoor seed-starting at my organic market garden, and now, eight years after my purchase, I’m approaching my 200,000th soil block.

Using a soil blocker has a lot of advantages. For one, it’s a much cheaper way to start seedlings than buying either peat pots or those little expandable peat pellets. What’s more, it lets me prepare my own compost-based soil block mix or recipe. This not only costs less than buying a soil mixture, it also means I can control the content so I’m adding fertility to my garden every time I plant a block.

My soil-block maker, or soil blocker, is a small, spring-loaded tool that shapes and ejects four 1-3⁄4-in. cubes of compressed potting mixture. Each block has an indentation in the center of the top where you plant the seed. Blockers like mine cost $25 to $30 and are widely available from garden supply catalogs.

After experimenting over the years with different soil mixes, I’ve come up with one that works well for me. A number of the ingredients are close at hand in the garden or neighborhood and are usually free for the asking. If compost excites you, as it does me, here’s a project you’ll enjoy because compost is the main ingredient. There’s something energizing about the musty-smelling, crumbling “gold” and its promise of great things to come.

Stirring up the recipe
A good soil mixture must be fibrous enough to hold together through many waterings. I use a fine-grade peat moss to supply this “glue.” Sand is added to allow air to pass through and to improve drainage.

This is my recipe: 3 parts fine peat moss, 4 parts year-old compost, 1 part sand, 1⁄8 part dolomitic lime, and 3⁄4 part fertilizer mix made from 1 part rock phosphate, 1 part kelp meal, 1 part seed meal or blood meal, blended and aged for three months.

Mix the ingredients well in a wheelbarrow or pail. Add one part water to every three parts mix, making sure all peat moss and compost lumps are broken up. Let the mixture soak overnight.

If you’d rather buy a mixture for soil blocking, look for one that contains peat moss, perlite, lime, and an agent that retains moisture. The last ingredient is the most important, since the key to success with soil blocks is that they must be well drained but moisture retentive. You definitely want lime in the mixture to counteract the acidity of the peat.

Punching out the blocks
Now the fun begins. Your mixture should be like a paste. It’s better for it to be on the wet side; if it’s too dry, your blocks will crumble as they’re punched out. Excess water will be pressed out in the blocking process. Gather mesh trays or wooden flats or any containers that are easy to pull around in the garden when planting and that hold just enough blocks so they fit together tightly. This prevents the blocks from drying out too fast.

Plunge the blocker into the mixture, twisting as you push it down so the blocker will be as full as possible. An alternative method is to spread out a 3-in. to 4-in. heap of mix on a hard surface, and press the blocker into the mix. Then turn the blocker toward you, and use your fingers to add more mixture. Make sure each cube is filled tightly by pressing it against the palm of your hand. It is important for the blocker to be absolutely and firmly packed.

Scrape off any extra soil from the bottom of the blocker, and set the blocker in whatever container you’re using. Now, punch out your blocks. If they crumble, try adding more water to your mix.

Planting the seeds

I seed all my crops this way except for carrots, beans, and peas. Carrots don’t do well in soil blocks because of their long root, and beans and peas are easier and quicker to seed outside. I place one seed in the center of each block and leave the seed uncovered. For the crops I grow, I’ve found germination is greater when seeds aren’t covered. More oxygen reaches each seed.

Place the trays on a heated bench or, later in the season, in a protected place outdoors. Keep the blocks moist at all times. After the first true leaves appear, fertilize weekly with a manure tea or diluted liquid fish fertilizer.

One year, birds discovered a tasty lunch in my newly planted seed blocks, and the quail enjoyed a salad bar of juicy young lettuce. Now, I tuck row cover fabric like Reemay tightly around the flats to prevented unauthorized snacking.

Getting the block in the ground
For best results, plant your seedlings outdoors as soon as roots appear. Seedlings can hold on for a short time, however, as the roots are “air pruned,” and they will not become pot-bound. Plant the moist seedlings firmly in the garden soil, and water them well. Since the soil blocks retain water better than peat pots or pellets, no special care is needed after planting.

As the garden vegetables are plucked to eat, I replace the harvested items with new seedlings in their soil blocks. My almost whimsical purchase eight years ago has given me a practical way to a bountiful harvest, as well as the chance to spend hours in a productive process that also leaves my mind free to meditate and reflect. My soil blocker is the best bargain I ever found.

For links to articles, blog posts, and videos on starting vegetable and flower seeds, see All About Starting Seeds.

by Tina Fraser
February 1997
from issue #7


posted in: soil, seedlings

Comments (12)

AlexVardy writes: Hey thanks for share this great information
Posted: 8:58 am on August 14th
glenmay writes: These are good seeds.
Posted: 2:21 am on August 4th
toriwilson writes: Hey that's great
Posted: 11:36 am on August 1st
KayClayton writes: Best of the Best, really well said

Posted: 6:51 am on July 4th
DianaRey writes: i like the bg! really nice.

Posted: 6:51 am on June 23rd
Rander12 writes: Great post
Posted: 2:35 am on February 18th
RandyFish writes: wow… its awesome! very nice.. u did a gooood job
Posted: 2:01 am on February 18th
RixonJoy writes: Impressive dude
Posted: 12:23 am on February 16th
AliceFulter writes: Lovely post
Posted: 5:58 am on January 26th
nicholassscott writes: Very impressive.. Really good
Posted: 2:49 am on June 3rd
David_Behkam writes: BRAVOOOO... Very Well...
Posted: 7:37 am on May 12th
PEAPICKER writes: New to site and new to using a soil blocker...but now trying this method using heat mats and grow lighting. Having some success with first batch but think I put varying amounts of soil blocker mix to cover each seed...think thats my problem as I have same seeds germinating in different time frames...varying as much as 8/10 days. I think I have the moisture correct for the soil block and I am bottom watering and even misting the tops of each block several times a day as I am retired. I bottom water every 2/3 days and let blocks soak until they look good and wet. Wondering if you should keep the soil blocks in darkness until seeds germinate covering your tray with black plastic?...then put them under grow lights. I have a timer for all of this and a device that is suppose to keep your heat mat at what ever temp you desire and it seems to work to a degree. Am in a garage where temps are not as warm as inside heated space but that doesn't seem to bother them.
Since this is my first batch I find myself wondering what I did wrong to have such a difference in germination time and guess its because I covered the seeds with varying amount of soil blocker mix. Wondering If I should just not put anything over them and just make sure the seeds stay moist.
I'm not the most patient person and am learning that you need to be and have the faith and am sure I will be experimenting to try to figure out a tried and true way to do this that works for me.Their seems to be many soil mix recipes that folks use and at this time I don't have any compost but am in the works to get stuff to do that with. I have collected about 150 large bags of shredded leaves and will be looking for some hay to mix with this along with grass clippings this spring and summer and all of the different things you can add to your compost to get a proper mixture.
It is going to be a fun spring and summer to me to see if I can make any quality compost to use for my soil blocking. Am also in the process of learning how to save seeds which is an entire different learning process but I think I can do it. I hope next year I won't have to spend very much to be able to have my seeds started and have a good vegetable garden. Keeping my fingers crossed. Have been a gardener for 40 years but never had time to do this process but since I'm retired I have plenty of time!
Posted: 10:45 am on March 4th
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