Why I start seeds in Soil Blocks

Why I start seeds in Soil Blocks

I have been using soil blocks since I started flower farming and I find it to be a fantastic, if not perfect, method of starting seeds. Here, I will go through why I love soil blocks.

First of all, I’ll just explain what soil blocks are; the clue is in the name! Soil blocks are made by using a mould (called a soil blocker) to create cubes of medium in which seeds grow. I will go into more detail about how I make the blocks and sow the seeds on a later blog post. 

So, what is so fantastic about soil blocks? Why are they becoming ever more popular amongst small-scale growers (they are used in lots of larger companies to grow e.g. lettuce). Well, firstly, the quality of seedling that is produced is really fantastic. The main reason for this is because the roots of seedlings do not become pot-bound, as they might in the plastic modules that are often used. Rather than growing round and round the module, the roots in seed blocks just stop growing, causing other roots inside the plant to grow inside the block. This is known as “air pruning”. When the plants are then planted out (or potted on into a larger block), they are ready and raring to grow. My soil block-grown plants in the greenhouse right now have lots of lovely, white roots, rather than the brown ones that can occur in modules. 


The next reason I love soil blocks is just how many seedlings can be started. The mini blocker creates 20 blocks which can easily fit in old takeaway containers (I got loads off my neighbours from their lockdown takeaways!). This means I can fit 300 seedlings on my two heat mats. I think that the same number of seedlings in traditional modules would take up 4 times the space. Also, using such little blocks means I just don’t use so much compost. This keeps costs down because I can use my homemade compost rather than having to buy in bags of compost.

This links to another reason that makes soil blocks so fantastic - not having to buy so many plastic modules. You know the ones I mean - bright green plastic that feels quite flimsy. From previous gardening experience, I have found that these just don’t last, no matter how well I looked after them - the plastic starts to degrade with time and weather and breaks down. I am trying to avoid microplastics in my garden, so using soil blocks really solves this problem. Yes, I do have to use the takeaway containers, but these are much more robust and they are being reused. 


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