Sunday, March 15, 2009

My Experience with Soil Blocks for Seed Starting

When I start plants from seed I use the soil block method instead of using plastic pots or other methods. I started using these in the 1990s. This soil mix is made with organic materials and uses compost as one ingredient. The soil is rich in nutrients which helps the seed grow into a strong seedling.

I am gearing up to plant seeds to grow indoors under lights and so soil blocks are on my mind. They were not common at all when I began using them. I wondered if they were still rare today so went online to do an Internet search. I didn’t find much information. I did find one website where someone asked a question. I decided to share my experience and opinions. What I said is in this blog post.

The question asker and some of the commenters echoed some of the same queries. The question was that a person who had not yet used soil blocks was getting reading to make some two inch blocks and was concerned with the over $100 cost of the 4 inch soil block maker mold/tool. He was using the same resource as I used, an Eliot Coleman book. The recipe for the soil mix includes peat moss. Someone else mentioned that they wanted to use sustainable materials and worried about using peat moss. Tips and suggestions were also requested.

The book recommends using three sizes of soil block makers, a one half inch block for germination, a two inch block for the next step and then a four inch block for some plants.

I saw Eliot Coleman use this method on his gardening television show. Later I read about the method and his recipe for the soil mix in his book “The New Organic Grower”.

Title: The New Organic Grower
By: Eliot Coleman

I am not going to share the recipe for the soil mix as stated in Coleman's book. Why? Because it is protected by copyright. I abide by copyright laws.

This is a very helpful and useful book that provides good information for the home organic gardener, and in fact, has more than a home gardener will ever use, so it is a bit of overkill, which is better, I think, than a book of little substance fluffed up with white space on the page and large font! Anyhow let’s support Eliot Coleman and buy his book if possible, hey it is less than $14 new on Amazon, which is less than the cups of three fancy cups of coffee at Starbucks!

Here is my reply:

I have an opinion and my experience to share with you. I began using the soil block makers using Eliot Coleman's recipe in the 1990s. When I purchased my soil block makers I believed what I read that I needed all three sizes so I bought all of them at once. Through years of successfully using the soil blocks I discovered all I need is the two inch size and I wasted my money on the smaller and the four inch size. I advise you to just buy the two inch size. If you really feel you need the four inch one and can afford it, you can choose to buy it now or next year. Here are details.

1. I don't like using the tiny ones to start seeds then moving them to the two inch block. I found it took too much time and it was just easier to put seeds in the two inch block. I also use two seeds per block just in case only one germinates. Truth be told usually both germinate and I have to pinch one off.

2. I only used the four inch block once. I found it was again more work for no real benefit. Those four inch blocks take a lot of soil to make to get so compressed. It is a couple of hours more work to make them too and I personally look to save time and energy. Most of the seeds I was starting were tomato plants (heirloom late season tomatoes). With proper timing and giving the seedlings a good weeks in the two inch blocks then promptly transplanting them to the garden they are fine strong plants with root growth right to the edges of the blocks.

In other words the two inch block did not hinder the root growth in my opinion, and the seedlings are 3-5 inches tall, good enough for me. I wonder if those growing in colder regions (like Eliot Coleman) who want bigger seedlings that perhaps grow them longer indoors and then have a shorter growing season than me need larger seedlings at transplant time to yield fruit before first frost? (I garden in zone 6.)

3. Back in the mid-1990s in a garden catalog I bought wooden crate things designed to fit the standard 99 cent plastic seed starting trays. I buy those cheap plastic trays and set them in the wooden crate which makes them strong and easy to move around.

I put the soil blocks nearly wall to wall in that tray. After putting the seeds in I use vermiculite as the covering on top of the seeds. I put and always keep water in the bottom of the tray (it has grooves). Properly made soil blocks don't fall apart when wetted in that way. Before germination I use plastic wrap on top and water twice per day from the top, gently, and sometimes use a mister sprayer, to keep the top moist. (Seeds that dry out do not germinate or tiny seedlings dry up and die.)

After shoots come up I remove the plastic and make sure to keep the water in the bottom. The blocks stay entirely moist due from soaking up water from the bottom up. (Those cheap plastic trays get reused for many seasons and therefore is not wasteful. This year I will also use for trays, some repurposed refrigerator bins from a broken fridge that went to the dump, they are strong plastic, even though they have no grooves and are less ideal for watering purposes.)

4. I use the standard recipe for soil mix found in the Eliot Coleman book.

5. My seeds are grown indoors near the furnace in the basement so there is some heat there, I have never used heaters.

6. My biggest challenge is labeling the seedlings! I make a diagram on paper and mark the tray with a letter (tray A, tray B, etc.). I make a note about which is top and which side is the bottom on the tray. On the diagram I note what variety is planted where. Organization is vital with this system. I can't use normal plant markers as they can't stick into the blocks.

When transplanting the seedlings you have to be careful about labeling plant markers so you know what went where in your garden. Again a clear mind is needed for that task that day!

7. Tips on block making. I mix the big mixture in the wheelbarrow and make the blocks outdoors as it is messy. I scoop some mix into a bucket and add water that I think is enough. I use a plastic tray like a dishpan on a table. I put some of the wet mix in it and make the block there. What I do is scoop and push it in until there is more than enough. I then compress well, in the dishpan and some water squishes out. I peek at it to make sure the bottom is flat and it is all filled, then move it to the tray, and pop them out.

If the soil block is too dry the block won't be formed well and will fall apart. If it is too wet it falls apart and won't come out of the mold in one piece. You will learn through trial and error how moist is just right. I try not to handle them too much as they can fall apart. They do get stronger when they dry out more but in that initial step mine are a bit delicate. Any that fall apart just get tossed back for a re-do.

8. Regarding transplanting tomato plants. If the seedlings are too leggy or taller due to something like having to delay transplanting for a week due to weather or whatever else interrupts the plans, do not worry. I transplant them with much of the stem lying horizontal in the hole. Roots will grow all along that stem and your plant will start off shorter and stronger.

External Links

Eliot Coleman's website, Four Season Farm

Amazon now sells the soil block makers!

Here is the one I use:

I own these but don't use them: the mini and the giant:

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12089thstreet said...

EXCELLENT post! I'm wanting to try soil blocks, but wasn't sure what size to buy. This post has helped me to decide. Thanks!

Sean said...

the 4 inch blocks are very useful
for starting corn in cool regions
such as the pacific northwest.
the corn root system gets too
large too quickly for 2 inch blocks to be much use beyond germination.

kathy said...

Loved all your great soil block advice. I'm using a 2" block for the first time. It's been great, but so many roots are coming through my tomatoes, and I wondered if I should transplant them before planting outdoors. I live on the North Fork of LI and we usually don't plant tomatoes outside until Mother's Day.
I didn't think I started them too early!

Gardeningbren said...

Thank you..this was very informative. I was looking for information on what to keep the blocks in...and you have offered the option of a tray with ridges on the bottom. I note Johnny's seems to be selling soil block propagation trays with wide mesh so I wondered if soil blocks need air all around?

christinemm said...

I use the cheap seed starting trays from any garden shop or Home Depot. They usually are 99 cents by themselves. If they only have the set in stock with the plastic lid they can cost up to $4 for one set.

Usually those cheap seed trays have ridges on the bottom. I do not think they need air on the very bottom but if the trays have ridges some parts get air and some do not.

I pour the water into the tray and let the water suck up from the bottom of the block. I find that too much top watering even gently, can erode the soil blocks.

I have been doing it that way for years with success.

The only tricky part is germinating the seed, that the top does not totally dry out and not let the seed germinate. I sometimes cover it until they germinate (with Saran Wrap) or a hard plastic lid if I have one on hand.

Do not over-analyze this just try it and you will see it is easy.

Val said...

Hi Christine,
First of all I loved your post. I've decided to try soil blocks this year (I usually buy my seedlings) and I've been trying to read everything I can find about them. Have you had any problems with mold on the outside of the block?

ChristineMM said...

Hi Val, No I have never had mold on the outside of the block. My mix uses compost which is alive and has anti bacterial and anti fungal properties.

I wonder if air flow is an issue causing the mold or if it is microorganisms in the block. Don't know.

Jordan von Trapp said...

Yay Christine! Thanks for this! I am a fellow soil-block enthusiast and I feel the same way about the 2-incher. I was telling my readers about blocks today and did some googling to find out if anyone had the same sentiment on saving time and cutting out the minis. Id like a large one for artichokes and peppers but the expense is prohibitive. Might figure out how to make one... Cheers and I look forward to reading about your homeschooling adventures when we decide to have kids... :)
Cheers, Jordan von Trapp

ChristineMM said...

Howdy folks, (Yes I am using Texan lingo) here's another blog post I did with a photo of the soil blocks from 2010.