Soil Blocking for Cannabis: tips?

BatmanPetersenc · Apr 6, 2024

Hello all. Quick question:

Is anyone using soil blocking to start seeds or clones? I've been doing it for my last few rounds and it seems like a great way to reduce on seed starting cubes, etc., and go straight into either my 2x4 indoor no-till or up pot as needed for an outdoor grow. (Pics below)

In an effort to refine my technique, does anyone have soil blocking tips, tricks, drawbacks, etc?

(Right to left: Tomatoes, peppers, cannabis tomatillos, chives, and a bunch of flowers.)

GNick55 · Apr 6, 2024

geezus no,.. waaaay to wet,..

BearWater · Apr 6, 2024

I bought one of those fiskers soil block press things and that’s as far as I got with it! it was intended for the veggie garden stuff. I’ll probably never do anything other than solos when starting ganja plants.

BatmanPetersenc · Apr 6, 2024

GNick55 said:
geezus no,.. waaaay to wet,..

Yes that tray I think ended up over watered. Unfortunately, it was the one with my cannabis in it, and the whole tray suffered. Once transplanted into the 2x4, and a few nursery pots most have bounced back, thankfully. I started three more cannabis seeds just in case they didn't.

Out of curiosity, is that soil blocking specific advice, or just general? Thanks for the reply!

BatmanPetersenc · Apr 7, 2024

BearWater said:
I bought one of those fiskers soil block press things and that’s as far as I got with it! it was intended for the veggie garden stuff. I’ll probably never do anything other than solos when starting ganja plants.

Yes, originally intended for veggies, but I figure why not for cannabis as well? Works great for the garden so far. Thanks for the reply!

Mikedin · Apr 7, 2024

BatmanPetersenc said:
Hello all. Quick question:

Is anyone using soil blocking to start seeds or clones? I've been doing it for my last few rounds and it seems like a great way to reduce on seed starting cubes, etc., and go straight into either my 2x4 indoor no-till or up pot as needed for an outdoor grow. (Pics below)

In an effort to refine my technique, does anyone have soil blocking tips, tricks, drawbacks, etc?

View attachment 2145964

View attachment 2145965

View attachment 2145962

View attachment 2145963

(Right to left: Tomatoes, peppers, cannabis tomatillos, chives, and a bunch of flowers.)

View attachment 2145961

i just picked up a soil blocker but I think the cubes are way too compact for weed seeds, I try to make my mix as light and fluffy as possible for seedlings, the blocks are awesome for garden veggies though!, I would consider using it if I picked up the 3/4” cubed maker and then moved them up into the 2” cuber with 3/4” nibs

What was your mix you used for your soil?

HerbalEdu · Apr 7, 2024

yeah aerated medium is essential for cannabis seedling, will work but seem too compact to me as well.

figolus · Apr 7, 2024

I use light mix soil , directly in the pot of 1l, i dont use rootsriot or other cube , have u triyng mixed coco and soil ?

BatmanPetersenc · Apr 7, 2024

Mikedin said:
What was your mix you used for your soil?

It is an off the shelf mix, cut with a small amount of coco and about 30-40% perlite. I agree it seems too dense, like a fudgey brownie vs. a cakey brownie. My partner blocked these cubes, so I didn't have the control i have had in the past, and don't have great notes this time. Thanks for your comment!

HerbalEdu said:
yeah aerated medium is essential for cannabis seedling, will work but seem too compact to me as well.

Absolutely! I've got a bunch of perlite in there, though maybe not enough, and it doesn't really show in the pics. I agree, these were too compact, too dense. Thank you!

figolus said:
I use light mix soil , directly in the pot of 1l, i dont use rootsriot or other cube , have u triyng mixed coco and soil ?

Thank you for the reply. I've previously started in soil/paper pots, peat cubes, rockwool cubes (i think) and these soil blocks. No problema with germination in any of them, but this time the seedlings got stunted, i think from watering issues, likely compounded by these dense blocks. I also wonder if I missed my transplant window and they suffered.

I have started three more plants in less tightly pressed blocks, with about 50/50 perlite to soil ratio. Will see how they develop.

While I understand that nobody else using soil blocks for cannabis is likely a sign of it's effectiveness, I'm just curious if I can make it work well enough. Thanks for the feed back everyone!

HarryMannbach · Apr 14, 2024

I’m relatively new to cultivation (5 plants, 2 grows), so take anything I say with a grain of salt (or a mol of salt)…

But I recently started two seeds in soil ‘blocks’, and they couldn’t be happier. We were starting our veggie seedlings for the year in the grow tent, and those all go into blocks, so I figured “what the heck?”.

Granted, I didn’t use either our smaller blocker (as pictured by @Mikedin ), or the larger one that the smaller one is intended to “plug” in to (pun(?) intended), and just formed balls slightly larger than a fist, then squished the bottom down a bit. I don’t have the recipe we used off hand, but as it was too dense for our brassicas and eggplants to be happy, we didn’t keep the recipe close at hand. That said, the density wasn’t a problem for my two girls. But, we replanted the struggling veggies in premixed soil from Tilth (highly recommend checking them out, and they also have a cannabis specific soil) and that stuff blocks up beautifully!

Anyway i’ve added a glimpse at how the two ladies are holding up with blocking. Clearly it can workout just fine! I like that I can essentially pause photoperiod plants until the whole tent is free and ready for them.

Anyway, just my 200 cents!

BearWater · Apr 14, 2024

HarryMannbach said:
I’m relatively new to cultivation (5 plants, 2 grows), so take anything I say with a grain of salt (or a mol of salt)…

But I recently started two seeds in soil ‘blocks’, and they couldn’t be happier. We were starting our veggie seedlings for the year in the grow tent, and those all go into blocks, so I figured “what the heck?”.

Granted, I didn’t use either our smaller blocker (as pictured by @Mikedin ), or the larger one that the smaller one is intended to “plug” in to (pun(?) intended), and just formed balls slightly larger than a fist, then squished the bottom down a bit. I don’t have the recipe we used off hand, but as it was too dense for our brassicas and eggplants to be happy, we didn’t keep the recipe close at hand. That said, the density wasn’t a problem for my two girls. But, we replanted the struggling veggies in premixed soil from Tilth (highly recommend checking them out, and they also have a cannabis specific soil) and that stuff blocks up beautifully!

Anyway i’ve added a glimpse at how the two ladies are holding up with blocking. Clearly it can workout just fine! I like that I can essentially pause photoperiod plants until the whole tent is free and ready for them.

Anyway, just my 200 cents!

“root balls”

GNick55 · Apr 14, 2024

HarryMannbach said:
I’m relatively new to cultivation (5 plants, 2 grows), so take anything I say with a grain of salt (or a mol of salt)…

But I recently started two seeds in soil ‘blocks’, and they couldn’t be happier. We were starting our veggie seedlings for the year in the grow tent, and those all go into blocks, so I figured “what the heck?”.

Granted, I didn’t use either our smaller blocker (as pictured by @Mikedin ), or the larger one that the smaller one is intended to “plug” in to (pun(?) intended), and just formed balls slightly larger than a fist, then squished the bottom down a bit. I don’t have the recipe we used off hand, but as it was too dense for our brassicas and eggplants to be happy, we didn’t keep the recipe close at hand. That said, the density wasn’t a problem for my two girls. But, we replanted the struggling veggies in premixed soil from Tilth (highly recommend checking them out, and they also have a cannabis specific soil) and that stuff blocks up beautifully!

Anyway i’ve added a glimpse at how the two ladies are holding up with blocking. Clearly it can workout just fine! I like that I can essentially pause photoperiod plants until the whole tent is free and ready for them.

Anyway, just my 200 cents!

you shouldn’t be misting your plants indoors,..

BatmanPetersenc · Apr 14, 2024

HarryMannbach said:
I’m relatively new to cultivation (5 plants, 2 grows), so take anything I say with a grain of salt (or a mol of salt)…

But I recently started two seeds in soil ‘blocks’, and they couldn’t be happier. We were starting our veggie seedlings for the year in the grow tent, and those all go into blocks, so I figured “what the heck?”.

Granted, I didn’t use either our smaller blocker (as pictured by @Mikedin ), or the larger one that the smaller one is intended to “plug” in to (pun(?) intended), and just formed balls slightly larger than a fist, then squished the bottom down a bit. I don’t have the recipe we used off hand, but as it was too dense for our brassicas and eggplants to be happy, we didn’t keep the recipe close at hand. That said, the density wasn’t a problem for my two girls. But, we replanted the struggling veggies in premixed soil from Tilth (highly recommend checking them out, and they also have a cannabis specific soil) and that stuff blocks up beautifully!

Anyway i’ve added a glimpse at how the two ladies are holding up with blocking. Clearly it can workout just fine! I like that I can essentially pause photoperiod plants until the whole tent is free and ready for them.

Anyway, just my 200 cents!

Absolutely, I've use the soil blocker for the last few rounds. It does work well enough. Thanks for the input!

HarryMannbach · Apr 14, 2024

GNick55 said:
you shouldn’t be misting your plants indoors,..

You should while they're in soil blocks.

Not after they're in pots/bags/hydro, granted. But soil blocks, along with just about any potted soil, should be drying out a bit between waterings. And given that soil blocks have a lot of peat in them --which is quite hydrophobic for a little bit when it dries out, before it becomes ultra-absorbent-- the misting provides a light layer of moisture that more readily re-wets the peat so that it can in turn more readily absorb the water at the bottom a blocking tray. On top of that, there is a veritable sh!tload of airflow in that tent. Think 4 fans for a 2'x4'x7' tent. So we're not concerned about fungal growth at this point. There's still way more airspace than greenspace in there. Seedlings, after all.

Not to over-explain, but I also don't want anyone coming across this to be under the false presumption that you shouldn't be misting your soil blocks, _regardless_ of what's growing in them. Granted, hemp/canna plants don't really need, or benefit from, soil blocking in particular... but it's also not a detriment in any way when done correctly. It's just a nice way to, if you're growing photos rather than autos, be able to hold their growth in the seedling/young plant stage if you happen to be an indoor grower who doesn't have a full space to dedicate to them for x weeks. Or if you're an outdoor grower who wants to get them started indoors while you await the arrival of a frost-free date, if your growing zone is beholden to them.

HarryMannbach · Apr 14, 2024

BearWater said:
“root balls”

Getting there, anyway

albitross · Jul 3, 2024

HarryMannbach said:
You should while they're in soil blocks.

Soil blocks should be bottom watered as much as possible. They sell specific capillary mats for this purpose.

I soil blocked many of my vegetable transplants when I ran our CSA years ago, just dusted off the apparatus to give it a try with autos.

BrentBanks · Jun 4, 2025

Responding to an old post.
I live in SoCal and only grow outdoors, it’s nice to be able to move the seedlings easily depending on the weather.
I’ve had several great crops using soil blocks.
I use the large blocks with a mix of peat moss, kellogg Raised Bed & Potting Mix (sifted), and Vermiculite.
After the seedlings are established I transplant to 1gallon bags, then to 20 or 25 gallon bags.

KolaKing · Jun 4, 2025

So I'm not really seeing the advantage of a soil block vs a rock wool block. I get the whole "in its natural state" thing but rock wool has the advantage of being less prone to overwatering. I also agree that the blocks look a bit dense but if it's working for you in cannabis then great! How do you keep the blocks together when they are watered? I would think that eventually they are going to deteriorate after repeated waterings. How hard are they to transplant as they don't have a container to keep the soil from crumbling in your hands?

Could you do the same thing but put the soil in a plug pack and sprout seeds that way? Same idea but now its got sides to support the media.

What, in your opinion, makes soil blocks a better alternative to rockwool blocks? Can't be price because rockwool is cheap.

Freddiebest · Jan 16, 2026

I’ve had good luck keeping the mix on the denser side so the blocks hold shape but still breathe, and giving them a light bottom‑water instead of soaking so they don’t crumble. A gentle brush of mycorrhizae on the seed divot has been money for strong starts. If you want a broader context on growing and plant care, the full article might give you a nice extra angle without interrupting your flow.

Vetsgrow2 · Jan 17, 2026

ALL YOU NEED !! sprout them in these then into Solo-cups for 2 weeks then their last pot...5 gal for me. I start feeding 4 weeks after the pot transplant.

Soil Blocking for Cannabis: tips?

Soil Blocking for Cannabis: tips?

BatmanPetersenc

GNick55

BearWater

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BatmanPetersenc

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Mikedin

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HerbalEdu

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GNick55

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Soil Blocking for Cannabis: tips?

Soil Blocking for Cannabis: tips?

BatmanPetersenc

GNick55

BearWater

If you were a hotdog would you eat yourself?

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Mikedin

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figolus

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HarryMannbach

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BearWater

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