Multiblock seedlings: growing more in small areas (with less effort)
Some of you have been to my market stall and purchased seedling blocks that contain more than one plant. These are called multiblocks, and I first learned about them from reading Eliot Coleman. I get heaps of questions about these so thought I’d tell you a bit more about them. When making seedlings, you can put more than one seed per cell/block with no intention of thinning out later. While it doesn’t work for every type of plant, I’d recommend it as a technique worth trying due to the time and space savings it gives.
Which plants like multiblocks (and which ones don’t)
According to Coleman, some of the plants that can be multi-blocked and grown out to maturity include:
Leeks, onions, spring onions, shallots, sweetcorn, cabbage, broccoli, peas and beans, just to name a few.
I have not tried all of these yet, but I here’s what I’ve found so far…
- Spring onions/shallots
Great. Works every time. I plant 10-12 seeds per block and plant each block 15cm (6″) apart. You harvest by pulling the entire bunch or by cutting the tops when needed.
I was sceptical when I first tried onions but I was blown away by the results. I plant 4 seeds per block and plant each block 25cm (10″) apart (the normal spacing is 8cm or 3″). You don’t actually get any more onions over the area but you reduce seedling making, storing and planting out by 3/4. The onions simply push each other apart and grow to full size.
Sow a maximum of 4 seeds per block and plant each block 15cm (6″) apart. Harvest by pulling the whole bunch when they are golf-ball sized (they wont grow much larger than that in close proximity). Alternatively you can carefully pull one from the bunch as needed, allowing the others to keep growing.
- Broccoli and cabbage
This was hit and miss. A few broccoli plants have worked out well with 2 plants coming from one hole without any lack of growth. Others (including cabbage seedlings) have seen one grow well and the other not. This is due to been shaded out by the first plant. In this case, I have grown the first plant to maturity and then cut it down allowing the second to continue growing.
A word of warning: watch your nutrient levels
While I have had some very good success with the multiblock method, I have also had some less than perfect results. This is down to nutrient requirements. If you are planting more than one seed per cell/block, the food requirements also need to be increased for the seedlings by 2 to 10 times (depending on the number of seeds sharing a block). This means that the seedling needs to be planted out much earlier than usual.
As the food requirements are higher with multiblocks, success often comes down to the size of the cell. I use 50mm (2″) soil blocks using home made mix which contains a lot of food for the seedling. Since my blocks are so large I can plant them out much later when they are much stronger and more likely to survive.
The smaller cell you use, the smaller the seedlings will need to be when they are planted out. This means they are more likely to be destroyed by birds, slugs, snails etc.
The moral of the story is, if you’re multiblocking make sure you use large cells. Even better, buy a soilblocker and make your own blocks. It should last you a lifetime!
Want to learn more? Eliot Coleman’s book “The New Organic Grower” has a comprehensive section on multiblocking and some of the seeds that work with it. See my resource list for more information about this wonderful reference text.