Growing seedlings with soil blocks
Soil blocks are small self-contained blocks of lightly compressed soil that allows seedlings roots to be air pruned and allow plants to re-establish quickly following transplanting due to minimal root disturbance
– Richard Lee
Alison Sizer of Whitehorse Urban Harvest recently gave a group of Permablitz volunteers a workshop on soil blocks – here are her notes below:
Benefits of using soil blocks as a propagation method
- Minimal plastics
- Home compost and coir are sustainable inputs
- Large numbers of seedlings can be grown and raised in a small space
- Heat forced germination in suburban setting is possible (minimal space required)
- Seed germination rates are easily identified
- One to five seeds per block – reduces seed wastage
- No thinning out
- No transplant shock
- The next season or crop can be grown on while the previous matures in the garden
- Longer lead time to control weeds particularly for alliums
- Disease transfer via pots is eliminated
- Air pruning prevents root bound seedlings
- Seedling can be planted in wider range of conditions – large soil/root ball for each seedling
- Better options for working in upright position
- Seedling share does not involve plastic transfer
Seed raising recipe
Loads of available recipes on the internet, but really: use what you have! Alison’s mix is something like the following:
- 1/3 Coir – fine – 90 litres is $13
- 1/3 Compost – fine (sieved) home-made from chook yard
- 1/3 sand (More or less)
I like to use vermiculite to cover the seeds. This has completely resolved any damping off issues.
Seeding the blocks
- I use a skewer, pencil or toothpick (as a dibber) dipped in water to pick up individual seeds
- Add only one or two seeds per block.
- Vegetables that can be multi-seeded in blocks: Beets -4, Onions – 5, leeks -4, spring onions – 10, Broccoli – 4, spinach-4
Care of seedlings:
- Bottom water
- Feed with liquid solution when true leaves appear. Worm tea or other liquid. I use kelp tea too.
- Plant Block below soil surface. This prevents wicking of moisture from the soil block
Here’s a great video that uses the same principles shown by Alison.
For more information of Soil Blocks, check out Sustainable Garden Australia’s post.