I got a catalog from Johnny's seeds the other day and saw their soil block makers. I've been looking into them and I'm thinking about trying them to start my garden plants this year as an experiment. I'll make my own soil block maker to test and may buy the nicer ones if I continue using them. I do have a few questions about their use I was hoping you could help me answer.

One question is about the compacted soil. It's my understanding that with plants, especially young seedlings, you want to make the soil light and airy to allow it to spread it's roots easily. However, if you're compacting the soil enough to hold a block shape, does this not prevent easy spreading of the roots.

Another is about potting up. I've seen with ones from Johnny's Seeds, that they make an indentation the correct size to drop a 3/4" cube into the top of a 2" cube. Would it be preferable to just start the seed in the bigger cube if you knew it was going to need the extra room before transplant or would you start it in the smaller cube and transfer it up. Maybe you just put it in the bigger cube if you needed more time than you thought.

What signs are you looking for to indicate that it's time to pot up?

How durable are these? I know you water them with a wicking action, but how long do they last? It seems to me that they'd tend to want to come apart. Are they just meant for the short time period (~2months max) that you'd start a garden plant before transplanting it into the ground?

Lastly, for this Q&A, has anyone used these for cuttings with success. It seems like they might be good for that purpose. Thanks for the help.

Here are some links and pictures of the soil block makers for sale at Johnny's Seeds at Sue's request.



4 - 2" block maker In Use 2" and 3/4" blocks in tray

  • Hi Dalton. This is an interesting question. I've never heard of a soil blocker so I went to the website, but there are a number of different products on the page. Would you mind adding a link to the particular type of blocker somewhere in your question? Thanks! Sorry I can't help you with an answer. I'll be looking forward to learning about this. Feb 24, 2016 at 17:23
  • @Sue here is a link to the one on that makes 4 (2") blocks at a time: johnnyseeds.com/p-8087-hand-held-4-soil-blocker.aspx and here is a link to most of the others and accessories.johnnyseeds.com/…
    – Dalton
    Feb 24, 2016 at 18:17
  • Great - thanks for taking the time to post these! Feb 24, 2016 at 18:23
  • You're welcome. I think it looks like a pretty cool idea, so I'm happy to spread it around. I'll be experimenting and testing them this spring. Like Bamboo says, it can get expensive if you buy everything, but I have a lot of scraps lying around and there are a plethora of videos on making your own. I'll make a few on my own and if I really like them, I might invest in a multi block maker. I just wanted to get a little in the know info before I started, so I could make as few of the inevitable mistakes as possible. :))
    – Dalton
    Feb 24, 2016 at 18:28

2 Answers 2


I've never heard of a soil blocker, so have read with great interest the 'Instructions for Use' on the website. What they're recommending is a high peat mix with perlite or grit to create the soil blocks from, in fact, they give a recipe there as to how to make it. I'd be a little concerned about the inclusion of a 'bucket of garden soil' myself - garden soil varies enormously, and may contain pathogens. Given the ingredients in that recipe, they will likely be quite successful, assuming your garden soil doesn't contain anything nasty and is of reasonable quality, and your 'well decomposed compost' has been produced using a hot, aerobic process, and that you invest in the dome covers they suggest to stop the blocks drying out completely.

If, on the other hand, you were thinking of using any old seed or cutting compost and not using covers, there could be an issue, depending on the formulation of the compost or potting medium you've chosen.

And no, it wouldn't be preferable to start seeds off in the larger block, best to start with the small one and then pot on later because you want root development to be contained, not wandering all over the place with large gaps of soil between in a larger block. On the other hand, a larger block for cuttings might be more appropriate, but it depends which plant you're talking about. Whether you want to bother to invest in something that makes a specially shaped hole to accommodate the block and seedling you've grown is up to you.

I imagine the usual advice regarding potting up applies, although there may be more information on the site about this - it's usual to prick out when the seedlings have one or two true set of leaves, but in a block, you would probably wait a bit longer, depending on the variety of plant, maybe 4-6 sets of leaves, possibly more, because you'd need a fairly solid, well developed root system to be developed, or the block would fall apart when you tried to put into something larger.

It strikes me that all of this will work out quite expensive - getting the right ingredients for the block mix, the cost of the block makers themselves, together with covers, so frankly, I personally wouldn't bother. I've never had any trouble starting seeds off in trays, then pricking them out into either plugs or small pots and growing them on, but you may feel differently.

How useful or not blocks of soil would be for cuttings is hard to say - depends on the cuttings/which plants they are, and the size of the block you're using. I'm not sure I can see any real advantage over cuttings rooted in ordinary small pots.

  • thanks for the info. I'll probably have the domes on inside the house because the AC/Heat dehumidifies. I live in an area of the country that gets super humid summers, so hopefully they'll be outside once it warms up a little. I've see a lot of people who use a wicking pad under the blocks to keep them constantly moist. One of the benefits that these are supposed to have is that the roots come to the edge and get air pruned.
    – Dalton
    Feb 24, 2016 at 18:25
  • Also, I just asked about the starting size, because they suggested on another site that things like melon and tomato would need them, but didn't say whether to start them in smaller ones and pot up the 2" or whether to just start in the 2 inch.
    – Dalton
    Feb 24, 2016 at 18:25
  • It's possible that any large seeds may be best off in a larger block from the start, not sure why you'd need a larger block for tomato seed though...
    – Bamboo
    Feb 25, 2016 at 13:56

I tried this supposedly-plant-nirvana-inducing method one year.

Suffice to say that it was a one-year experiment. Some folks seem to love them, and write paeans to them, but I just didn't find much actual difference in my seedlings .vs. cell-trays. It certainly was more fuss. YMMV. But you sure can spend money on tools to do it with, which would be Johnny's angle on it, in my rather jaded opinion.

I, as you plan to, cobbled up my own blocker rather than enriching them. It made pretty decent blocks (I did buy materials for a proper mix.) Results did not encourage me to spend money on tools for it, nor to continue with it.

Keeping the blocks moist without causing them to fall apart while you are waiting for roots to grow is more of a problem than paean-writers admit to, as one experiential observation. When they get pretty full of roots they are moderately durable, but up until then they like to shed corners, and rather than "perfectly air-pruned" they ended up horribly matted together on the bottom, in the soil mix that fell down between blocks.

Presumably one point to the 3/4" block method would be that you don't make the 2" block until the roots have filled the 3/4" block, so it falls apart less than if you plant a seed in the 2" block. It also takes up less space when things have not germinated yet. But large seeds (cukes or squash) are liable to split a 3/4" block when sprouting.

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