A “soil block” is a square of potting soil that is compressed into a mold forming a block. When most people see them they mistake them as brownie’s. I honestly think I am more fond of soil blocking than brownies, and that’s definitely saying something because this girl loves chocolate!! Soil blocking is a method of indoor seed starting that has become soon to be very popular in the growing community. Instead of using a container to contain the soil that typically is used with starting seeds indoors, the compressed soil serves as both the container and the soil medium all in one!
Usually when seeds are started in containers the roots will encircle a container once they reach a certain size. With a soil block, instead of roots encircling a container, they are “air-pruned”. This allows for a seamless transplant with virtually no transplant shock. You can start seeds in soil blocking that are sensitive to transplant shock without disrupting the root system.
When I was first introduced to soil blocking I tried lots of different mediums to create my soil blocks. There are lots of different recipes on what to use and I tried them all. This was a step I will be honest I wasn’t crazy about so I explored different pre packaged seed starting mediums and landed and stuck with Pro-Mix condensed premium moisture potting mix.
The Compressed Premium moisture Potting mix from Pro-mix was surprisingly easy to make soil blocks with and was easily accessible at my local Walmart. Now I will be honest this is not the most cost effective way to soil block, as making your own medium is more cost affective but it is time consuming and takes up more room than I have. I went with the convenience of it and has worked great for me!!
There are many different sizes of soil blocks and lots of different options when shopping around for what works for you . I have found for me I always lean towards the large 4 block soil blocker from Gardners but is not for everyone. Most gardeners/farmers use the small soil blocker that has 20 cells . With the small soil blocker you can start a significantly larger number of seeds. I have found that with the small soil blocker I end up having to bump them up to a larger cell before I can put them out so I skip that step and just start them in the larger blocks to start with. To each’es own!!
When starting soil blocks you can use trays of any kind as long as they have a little ledge on the side for watering. I have used 1020 trays with no drainage holes , cookie sheets, cafeteria trays and more! When watering soil blocks you bottom water them . You poor water in to the tray and the blocks of soil absorb the water . I typically will go around and water them all once good and then go back around to where I started and water again after the initial water soaks in. I am known to over water and battle fungal knat’s and surface algae . I am that helicopter plant mom that over does it but and am hoping with more experience under my belt that will fade. You know its like the crazy things we did with our first child versus our 3rd child who when they get hurt , unless they are bleeding you don’t want to hear about it!! HAHA .
Depending on the seeds and time of year, where I start them varies. In the winter and early spring when the hours of daylight are low I will start my soil blocks inside my office under lights. I use your basic shop lights attached to metal racks. Once the seedlings get a few sets of leaves and are more mature and after hardening them off will put them out in my un heated greenhouse. In my office I don’t use heat mats and haven’t found that they are needed. I keep my office a consistent temperature of about 75 degrees Fahrenheit so its plenty warm in there. Out in my unheated greenhouse I have heated germination boxes that we made .
They work great for starting seeds in the greenhouse and have had great success with them . I am planning on writing a blog post on how we made them too so be sure to hold me to it!! So the seedlings that I start in my office that have matured go out in to the greenhouse to make space for more successions to be started in my office. I am very limited on space and try and get things out as soon as I can. From the greenhouse they go out in the garden in to caterpillar tunnels. The seedlings I start in my office go out to the greenhouse but I don’t put them on the germination boxes but on the other side where there is just shelves.
There they sit until they go out in the the garden under caterpillar tunnels in the winter and early spring. I try and give them as much protection as possible until our last frost date and historically that is right around mothers day. After the weather starts to warm up all my seeds are started in the greenhouse or direct seeded and the season gets a great deal easier!!
I hope you were able to learn a little bit about soil blocking and the amazing benefits that they have. They truly have changed the growing game in America since they were introduced and cut down on plastics a great deal!! Please be sure to ask any questions you might have on soil blocking and I would be happy to answer them !!