How to Do Proper Soil Blocking for Indoor Seedlings?

By Harry RamosLast update: 2024-07-11

Using soil blocks for indoor seedlings is one of the best methods to decrease transplant shock. It is also fun, eco-friendly, and easy to do, not to say that you don’t have to reinvest in seedling trays over again.

If you want to know how to do proper soil blocking for indoor seedlings, continue to read this guide.

How To Do Proper Soil Blocking For Indoor Seedlings

Prepare Enough Tools

To do proper soil blocking for indoor seedlings, you will need:

  • Some small cookie sheets or cafeteria trays
  • Soil block mix
  • Soil blockers
  • Dome lid (optional)

Determine The Right Soil Blockers For Your Seedlings

How to Do Proper Soil Blocking for Indoor Seedlings?

Soil blockers are easy to buy online and they are varied in sizes.

For those who are on a tight budget that only can purchase one size of soil blockers, choose the ¾” because they’re compact, soil-efficient, and fit most seeds from different species.

If you have a loose budget and are serious about gardening, we recommend investing in one more size – the 2” that works perfectly on really big seeds.

How to Do Proper Soil Blocking for Indoor Seedlings?

You can go for bigger sizes of soil blockers but we personally don’t prefer them because they need more soil to make a soil blocking but the final benefits on the seedling aren’t noticeable.

Make (Or Buy) Soil Block Mix

How to Do Proper Soil Blocking for Indoor Seedlings?

It is difficult to use bare potting soil for soil blocking because it doesn’t have good adhesion and break easily after drying. That is why you’d better mix it with additional perlite or compost.

The key here is to find out an appropriate soil mix recipe that is easy to find or buy in your area, has good adhesion to form a soil block, and suits your seeds’ nutrient requirement.

For non-experienced gardeners who want something convenient to use, purchasing premade soil from local vendors is a good idea.

How to Do Proper Soil Blocking for Indoor Seedlings?

If there is no premade soil mix available to buy in your area, searching online retailers. But note to purchase from reliable brands and take a look at the shipping cost before making your decision.

If the two options above are not possible for you, think about making your own mix. It’s easy; don’t worry!

We tested numerous soil blocking recipes and found that the one by Eliot Coleman is quite effective:

  • 20-quart compost
  • 10-quart potting soil
  • 1 cup greensand
  • 1 cup colloidal phosphate
  • 1 cup blood meal
  • 20-quart perlite or coarse sand
  • ½ cup lime
  • 30-quart peat moss or brown peat

Mix all the ingredients thoroughly with warm water in the ratio: 3 parts of soil and 1 part of water. The standard mixture needs to have the consistency of wet cement or soft putty.

Tips: If there is no peat moss or brown peat available in your area, use coconut coir instead.

How to Do Proper Soil Blocking for Indoor Seedlings?

We personally like coconut coir more for some good reasons:

  • Algae doesn’t grow on them easily even during cold days or when we overwatered the coir
  • Compared to peat moss, coconut coir has better adhesion; even after dried out, they don’t get fussy that much
  • Coconut coir is neutral while peat moss or brown peat is acidic
  • They are eco-friendly

The only flaw of this substrate is the high cost.

Besides, you can replace colloidal phosphate with bone meal, greensand with wood ash depending on the availability in your area.

How to Do Proper Soil Blocking for Indoor Seedlings?

Little known-how in checking whether your soil mix is wet enough or not

There are two common issues in the step of mixing soil with water – it’s either too dry or too wet. You can test it by throwing the soil mix to a vertical, flat surface, such as an old wall or a shed.

  • Soil doesn’t stick -> Too dry -> You should add more water little by little
  • Soil runs down -> Too wet -> You should add more soil mix

Things You Need To Know When Making Soil Blocks

Making soil blocks isn’t as easy as it seems. You might need to practice a little bit to create a complete soil block. Be patient!

Place a small bucket of lukewarm water beside you to rinse the soil blockers in between each batch

Make sure the soil block can sit flat on the floor or an even surface.

How to Do Proper Soil Blocking for Indoor Seedlings?

To make prettier soil blocks, pile up the soil 1”-1.5” deeper than the height of soil blockers

Find a flat, reasonably high workspace so that your body feels the most comfortable


After sowing seeds to the soil blocks, remember to water them frequently.

An easy sign to know that you’re under-watering is your seedlings start to get crispy. On the contrary, if you see algae start growing around the soil block, increase air circulation and reduce the amount of water.

That’s all for this article. Hopefully, you’ve got more useful information on how to proper soil blocking for indoor seedlings. Thanks for reading!

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