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About Potting Blocks

What are Potting Blocks?

Visserite Commercial Blocker of the Netherlands. Potting Blocks, also known as soil blocks, are free-standing compressed cubes of potting soil which hold their shape without any container. Potting Blocks are made from a zinc coated stainless steel Soil Block Maker, much like an ejection mold. The block maker metal form is packed into a tub of pre-moistened potting soil and then discharged into nice, firm, blocks with a pre-drilled seed or transplant holes formed right into the top. Potting Blocks are used for seed starting or germination, and transplanting. They have an amazing success rate due to the volume of soil compressed in the cube. The roots are naturally "air pruned" due to the air barrier of the "container-less" cube. They become the growing medium and the container! They are used for everything; herbs, flowers, vegetables, cuttings, and other transplants.

Potting Blocks have many advantages over traditional potting methods. First, they eliminate transplant shock! The seedling and root system stays intact and protected, a "home away from home". They will not become "'root-bound". They eliminate root circling. They replace plastic pots, trays, inserts,etc. They contain more cubic volume of soil than pots of the same top dimensions. They promote great air circulation. They have a major increase in space utilization than round pots. And, studies in Europe have shown that Potting Block transplants are superior in performance than container-bound transplants.


Where did they come from?
(Read more about the "Living History of Soil Blocks".)

Commercial Chrysanthemum Soil Block Farm  Soil blocks have been used in Mexico for over 2000 years! Has anyone ever heard of the "Floating Gardens" of Mexico City? Well, about the same time Christ was born, a small band of poor,semi-barbaric tribe of Aztecs in central Mexico were trying to find a settlement safe from other warring tribes. This tribe was know as the Xochimilcos (pronounced so-chi-mil-cos). They were inhabitants of the Central Valley of Mexico, a huge valley completely surrounded by volcanic mountains. After fighting with neighboring tribes, they decided to retreat to some islands on the shallow lakes of present day Mexico City, which have long since been drained. These lakes were caused by constant flooding of mountain runoff from rain and springs. There, on these
islands, in a land locked basin, they had to create a system of land reclamation. This land reclamation and subsequent agriculture is know as the Chinampas system. Chinampas farming is the most intensive and productive methods of farming that has ever been devised! It provided the Aztecs with land to live on and their first surplus of food they have ever known. This new wealth enabled them to quickly build standing armies and soon conquer all of Central Mexico, supported completely by Chinampas farming.

Misinterpreted as the "Floating Gardens", Chinampas are actually long narrow strips of land surrounded by water, like a peninsula. These strips of land were separated by drainage canals. From the depths of these canals, the peaty sediment and mountain runoff were scooped up and piled on top of the land strips, making them higher than the flooding waters. They would weave branches and live willow trees to anchor the rich, mucky soil in place. This created a moist planting surface. Every year another layer of fertile mud would be dug up and spread on top of the existing chinampa.

1939 Goradam Potting Blocker  The most essential element in chinampas farming is the seedling nursery technique. Here, the original soil blocks were created. At one end of the peninsula, the thick mud was spread over a wattle of weeds. After several days the muck would be hard dry enough to cut into little rectangular blocks called chapines. Then, the chinampero, or farmer, makes a little hole with his finger or a stick in each chapine, drops the seed in the hole and covers with a little manure. They were watered in the dry season and covered with reeds in the winter to protect from frosts. The seedling is then transplanted in the chinampa, which was leveled and hoed using a digging stick, or coa. Finally, it was covered with a thick layer of fertile canal mud. The Xochimilcos raised corn, beans, chili peppers, tomatoes, and amaranth. Flowers were also grown with this method. A dozen varieties of dahlias, and marigolds were grown for the altars of the pagan gods. Later, after the Spanish conquered the Aztecs, they continued to grow the native varieties and European crops like, carrots, lettuce, cabbage, beets, radishes, onions, carnations, roses, and lilies. See Real Pictures of Modern Day Chinampas.

Most recently developed in Holland, the potting blocker, is now made of a zinc coated prefabricated steel. They have been in use there for about 100 years. The Dutch are the oldest known users of ‘perspotten’ (soil blocks) in Europe and have used them since the late 1890's. Europeans have been using potting blockers for market gardening for decades. According to the Museum of Gardening at Harlow Carr London, UK, "Before 1939 large numbers of plants were raised annually in clay pots. These commonplace earthenware items required considerable fuel to fire them, and production ceased during the war. The solution was to make the growing medium self supporting. The moving parts of the soil block maker shown here are a hexagonal mould and a compacter with a hexagonal base and a bullet shaped centre. Each part slides on a pair of vertical rails and can be retained at the top with a spring clip. In use, the mould is loosely filled with compost, the compacter is brought firmly down with two hands, and finally mould and compacter are raised together. The block is then slid out. The compacter leaves a central depression which is filled with a pinch of loose compost, and in this the seed is sown." "The blocks are 7cm across, and the hexagonal shape allows close-packing on glasshouse bench or floor. A plate on top of the device is engraved the Goradam easy-one soil block maker."

The Ladbrooke Soil Blocker is the best made blocker on the market today. It comes in many sizes from small home gardener sizes to large stand up blockers for the commercial farmer. (See our soil blocker size chart.) Soil blockers have only been used, rarely, since the 1950's here in the U.S.A, and mostly from immigrants from the Netherlands trying to escape German occupation. The soil block transplants were wrapped in tin foil and sold by the dozen as flower or vegetable starts. They are increasing in popularity though, as high oil prices for plastics and environmental responsibility takes center stage.
 

What are the disadvantages?

my original Ladbrooke Mini 4 2The soil block gardening method needs attention. Although this may not be seen as a disadvantage to some, others may find it new to their gardening style. It is precisely why the soil blocks work so well, that they need extra attention paid to their needs. Rapid growth in the block requires constant monitoring of the watering. And, if growth is to be expected, than so does the proper timing of the "potting on" or transplanting. It is a horticulture fact that plants grow the fastest when they are given just a little more room to grow than their previous space. This requires precise timing as to when to transplant. Daily routines must be established to check for warmth, light, growth, water and weather. The very nature of soil block gardening means starting earlier in the spring or late winter. Paying close attention to weather to watch for "windows of opportunity" are part of the game of transplanting.

Showing wear of the zinc coating only after over a decade of hard useAnd, to some, the biggest disadvantage is the cost of the system startup. The block makers from Ladbrooke don't come cheap. At the same time, they are made by British engineers with the highest standards. They simply work year after year with no malfunctions. Some, have reported the cost of soil blockers to be prohibitive, and outweigh the benefits produced. Let's look at that. You can easily spend a few hundred dollars on equipment your first year. (But, you can invest in the micro 20 for your first year for under $30.00.) The "basic three", Micro 20 (3/4"), Mini 4 (2"), and the Maxi 1 (4"), will get you a maximum of 10,000 plants in one year without upgrading to commercial units. You will keep the same equipment for decades. You will no longer be purchasing plastic, which is always rising in price. You will no longer be cleaning pots and trays. You also don't need to have so much storage for pots. And, for fans of the Rockwool System, blocks can do the same thing, for only the cost of the potting soil, not the individual block.

We can say for certain, potting blocks are an investment that pay dividends your first year, completely pay for themselves in a couple of months, rise in value daily, while lasting for years and years. For myself, there are no disadvantages. When I set out to farm on my own, I started with soil blocks and soil block makers from the beginning. I learned the hard way: trial and error. But, I also proved the system worked and I worked to do it right and better. You all are enjoying the benefits of a decade of serious soil block experiments.

Just because you're on the right track doesn't mean you can just sit there.
-Will Rogers


How does a soil blocker work?
(See our How-to Pictorial.)

A soil blocker makes little compressed cubes of free standing potting soil. First, a large tub is filled about one-third of the way with the appropriate type of potting soil, know as the "blocking mix". It is moistened to the consistency of wet oatmeal, known as the "slur". Stirred well, it is left to soak up all the water for about one to three hours. This ensures that all the fibers in the mix are moist enough to bind or "knit" together, and the consistency holds the block upright. This is very different from using traditional dry filled plastic containers! You should be able to pick up a handful of slur and squeeze out a few drops of water. Then, it is perfect. Mound up the slur in the center, like a little hill. Now, one comes up to the tub with a blocker in two hands (or one hand with the smallest blocker) and, making sure the mound is three times the height of the blocker being used. Diving straight in and parallel to the ground the blocker is thrust in the mud and twisted back and forth. When the blocker hits the bottom of the tub, tilt back slightly to release the suction from the bottom and twist all at the same time and do it again. By the second or third thrust you should see some water oozing out the top. This is known as "charging" the block. You can't over pack the blocker. Once it is compacted, it must be "discharged". There is a spring loaded lever that is lifted against the handle when the blocker is placed where you want to release the blocks. Lift up the handle while pressing the lever and the blocks come sliding out, effortlessly! You can set them on pieces of wood, other plastic trays, a piece of plastic, or some hand made wooden crates, which we'll describe later. There sits a perfectly square molded soil block complete with an indented seed hole. They are strong, sturdy, a pot without any sides. Pick them up and move them around. Simply brilliant!


Why are they so great?
Less space, more soil, no pots, better growth.......

Scientific studies* have shown soil blocks to perform much better when transplanted than traditional methods like plastic pots, plugs, peat pots, compressed peat pots, or the Japanese paper pot. And, they sure are a lot cheaper than rockwool cubes! Researchers have also proved that plant roots grow better in cubes rather than tapered pyramid plugs*. It's all about the transplanting, and plants grown in soil blocks never know they aren't already growing where they're supposed to live! Why? The walls of the potting block are actually the air that surrounds it. So, when the root gets close to the air it turns backward and focuses it's growth in the center of the cube. This eliminates transplant shock! Plastic pots, on the other hand, encourage root circling and root rot; giving the plant a false impression of life!

Transplanting into garden soil will shock the plant and they tend to wilt and become stunted. But the blocks remain ready for explosive growth as the roots move out of the block into the garden soil at it's own pace, adjusting to the new air to moisture ratio. And, they're much sturdier than other transplants. The root ball is heavy and concentrated in the center of the block, so it is less likely to be affected by wind. It can also be handled easier. Pick it up and toss it to your neighbor. You'll shock them, not the plant! They don't fall apart. You aren't hacking away at their roots to get them out of the pot, you're not "pricking" them out of tightly knit flats with intertwined roots. Roots are their water and nutrient uptake system. You'll feel a lot better if you don't see roots!

The investment in potting blockers pays dividends immediately, and they free up so much extra time by eliminating the cleanup and sterilization process of plastic pots and plugs. There is also no more purchasing of plastic pots, trays, plugs, plugging machines, peat pots, etc. It beats the constant price hike in petroleum by-products! And, best of all, for large-scale growers, it eliminates the huge mounds of broken and deteriorated plastic pots and trays. This makes it an excellent environmental product to use. There are no breakable parts and they last for decades without any maintenance. Just keep them clean with a little rinse off so the organic acids in the soil mixes won't corrodes the metal.

This will ensure trouble-free use. Blockers are also highly regarded in Organic farming as the standard for quality. Potting blocks are also an efficient use of space. Potting blocks allow more plants per square foot of space than any round pot. And they won't get knocked over. You can build custom wooden trays that allow you to stack trays of blocks on top of each other. Because of it's cubic, rather than tapered sides, potting blocks contain 2-3 times as much volume of soil than a plastic pot of the same top dimension. For example, the 4" Maxi blocker has the same volume of soil as a 6" plastic pot, and can hold a transplant for up to 8 weeks!

*W.J.C. Lawrence, Catch the Tide: Adventures in Horticultural Research (London: Grower Books, 1980),pp.73-74
 

What about Peat pots? Aren't they biodegradable?

Many people use peat pots. They are supposed to be biodegradable. The pot and all are set into the garden. They are bound together with a lot of glue which inhibits roots growth and penetration. They often won't let all the roots out and you're left with a piece of trash in your garden. Or, the ones with less glue will fall apart before it even reaches the garden. Or, they'll drown in a pool of water because the pot doesn't drain properly. We've never had great results with them, anyways. The compressed pellets that expand open when water is added, are almost more trouble. They have already lost their water holding capacity thanks to the manufacturing process of wetting and dehydrating and compacting. And, at the end of the year your garden is filled with little, messy plastic nettings which do not breakdown!
 

How do you seed them?

The potting blocker makes it's own seed hole, or transplanting hole. This is a huge difference. Uniform, consistent, reliable, accurate holes are placed or indented on the top of the cube for you. This saves time and hassle of making it yourself (like our Aztec friends had to do). The potting blockers also come in a variety of seed hole makers know as "pins". The "seed pin" is the smallest and works well with small to medium size seeds. The "dowel pin" is deeper and works great for large seeds or cuttings. The "cubic pin" is 3/4" x 3/4" and indents a perfect little cube for potting the micro blocks (3/4") onto larger 2" blocks. The cubic pin also works great for huge seeds, or multiple seeds in one block. With all the different sizes, many seeds are sown in blocks that one normally doesn't associate with transplanting, like corn, peas, and beans.

You seed them with precision seeders, or by creasing a seed packet and tapping seeds in one at a time to prevent duplicates. You can use a wetted pencil, bamboo chop sticks, and toothpicks by wetting and touching the seed and then touching the soil block. It will stick because the soil is stickier than the seed held by water on the pencil.
 

What kind of potting soil should I use?

The soil in which blocks grow must be specially formulated or at least specifically blended. This medium is known as "Blocking Mix", or "Blocking Soil". While there may be many commercial varieties of potting soil available, mixing your own makes the very best. The reason being is that most potting soils do not contain real "soil". Good garden soil from your own carefully tended plot is a key component to the overall health of your transplants. Here, in your soil, lies secret ingredients: bacteria, fungi, nematodes, protozoa, beneficial micro-organisms, are known as the "good guys" and are actually protecting your garden from the 1% "bad guys".

Much like the Chinampas of Mexico, your blocks should be made from some of your own soil. But, blocking soil also needs extra fiber, like peat moss, coir fiber or peat plus coco peat, to ensure it won't fall apart when watered to a sticky paste, or slur. Peats add great water holding capabilities, since blocks have no pot to sit in and drink freely. Blocks also require good air porosity and drainage. This is where Perlite, asbestos-free vermiculite, and sand come to play. And, of course, compost. Blocks need compost, countless books being written on the stuff. The miracle maker, the fertility factory, the nutrient warehouse, compost. Good compost is well decomposed, and preferably comes from your own pile. We will get into good compost soon.

And finally, the icing on the cake is rock dust. There's limestone, the most important, if peat moss is used. Limestone sweetens the peat so it's not overly acidic. There are other rock powders, like colloidal phosphate, also known as soft rock phosphate. Glacial rock dust, from old glacial moraines, contain over 70 trace minerals. They give the transplants a "salad bar" option for nutritional requirements. Greensand, another mineral deposit from the ocean floor, is also used for it's trace mineral content. You can also add a slow release fertilizer, like blood meal, feather meal, cotton seed meal, shrimp or crab shell meal, or alfalfa meal. You must use only slow release nitrogen meals to germinate seeds successfully. Slow releasing nitrogen meals will not affect seed germination, because after the seed has germinated and used up it's own reserves, then the nitro meals will begin to break down into soluble food for the roots.
 

What kind of peat do I use?

Peat is partially decomposed plant residue from bogs and swamps. Peat is the planting medium of choice for most growers. It's lightweight, weed and disease-free, and holds 7-30 times it's dry weight in water while still providing air spaces. Peat contains valuable organic acids, which increase microbial action, which, in turn, releases nutrients for plant roots. But, peat is variable, and comes in many colors and lengths, and there are also many commercial varieties to choose from. There's black peat, from the bottom of swamps, white peat from the tops of bogs, and brown peat, from somewhere in the middle, peat from Wisconsin, Montana, Germany, Scandanavia, and Canada. Canadian peat is the most common, most popular, cheapest, and most plentiful, with the best qualities for the price. The best for potting blocks is sphagnum peat moss; milled and screened, medium fiber length, and medium brown in color. Be sure to find a peat moss without any wetting agents, additives, sticks or dust. It's worth the extra effort to find the best. Just make sure to have a 1/4" hardware screen handy in case a good peat needs further screening of longer fibers or a few sticks. We use Sunshine Peat Moss under the Sun-Gro label. Here, in the Northwest, this is the very best! Growers in the Midwest and the East can drop us a line and let us know the best out there.

The environmentally friendly alternative, Coco Peat is made from coconut husks left over after the coconut meat and milk have been taken. Coco Peat is an amazing alternative for those individuals who are worried about the environmental impact of peat bog harvesting. And, surprisingly, it works just as well, and maybe better! Coco peat can last three times longer than peat, giving you more organic matter in your soil for a longer time. It is disease resistant! And, it is superior in nutrient and water storage abilities. It holds 8-9 times its weight in water and comes with a balanced Ph of 5.7-6.8. Coco peat has been thoroughly tested and approved for Organic Agriculture. Coco Peat is hard to beat! We have used it extensively in potting block production, and really enjoy working with it. You must mix it half and half with your peat, as it can not knit together on it's own. It smells so wonderful, you could eat it! As it's popularity grows, so does the companies competing for your dollars. Always buy coco peat that is washed of excess salts, as coconuts absorb salt from the ocean water. Check for a balanced Ph, too. Coco peat comes in compressed bales or bricks. They will fluff up to 4-5 times their size. You can fluff it up by soaking it in warm water for an hour or two.

When using a balanced Coco peat, the limestone is omitted. Adding a little oyster shell does season it just right, though. Coco peat should be mixed with peat moss, though. Use about half and half. A final clarification needs to be made about coir fiber, also known as coir pith, or coconut fiber is not the same as coco peat. Coir fiber is longer, shredded made from the coconut pithy waste, and is a separate by-product of the coconut meat industry; whereas coco peat is the crushed, milled and screened coconut hull. Also, the best coconut fiber is composted and aged for 1-2 years, and is washed free of salt and ph balanced and also used in hydroponics. This is the only coconut product able to "knit" together to make perfect soil blocks. It's what we now use in our Old Farm Boy blocking mixes.

(Note: We give you the maximum coco peat ratio for stable blocks(50/50), but our farm uses 1/3 coco pith to 2/3 peat moss.)

Homemade mixes aside, there are commercially available potting soils that work just fine. We have used Pro-Mix quite successfully. We also sell our own private label potting soil known as Old Farm Boy (you know it's the best!). Others may be available, so try them all out if you don't want to mix your own. If you're an Organic grower, make sure to check the ingredients and compare with OMRI (Organic Material Review Institute), there are companies out there that claim to be "organic", but actually contain non-organic materials.
 

Environmental Note: Always buy peat moss from companies that have the label "Canadian Sphagnum Peat Moss Association". They are committed to the ecological harvesting of peat bogs that replenish themselves faster than they can harvest the peat.

I quote Eliot Coleman from "The New Organic Grower":
"Of the peat lands in North America, only 0.02 percent (2/100 of 1 percent) are being used for peat harvesting. On this continent peat is forming some five to ten times faster than the rate at which we are using it. And even if we don't include bogs located so far north that their use would never be economic, peat is still a resource that is forming much faster than we are using it. To my mind that is the definition of renewable resource."