Vermiculite

[JPB]

I use vermiculite in my pot mix (10-20%) with good results so far. What are your experiences?

Thanks, Hans

[Darren]

Hans,

I rarely use it in potting mixes for mature plants but it is excellent for adding to seed composts as it seems to keep mositure levels more constant whilst still allowing aeration. For this reason when I sow some seeds such as primula or central-asian Anemone I use it for covering the seed. It allows some light in whilst retaining moisture and is light enough for the tiny seedlings to push through easily.

[David Pilling]

I have seen it pointed out that you can measure how much water compost holds and how much air space there is in it, and that quite significant amounts of vermiculite or perlite or whatever are required to change these.

As a result I use something like 60-70% vermiculite with seedling compost for seedlings that appreciate good drainage.

[Darren]

That ratio sounds similar to mine David, when I mix the stuff in, though usually a part of that 60-70 % would be perlite. The other third would be a commercial seed compost. This mix is also good for bulbs where the high proportion of inert ingredients helps prevent the mix deteriorating or compacting too badly as the little bulbs often stay in this mix for two years.

[Giles]

Darren,
I was interested to see your comment on the use of vermiculite as a covering for primula seed, to keep the seed moist, but also letting light in, and not impeding emergence. I started using it for this purpose this year, with excellent results too:
(far better than gravel, or nothing at all)

[Ezeiza]

Vermiculite at first is grainy and crumby and as plants are watered it breaks down to a highly water retaining dust. That it is used for drainage does not reflect facts. It is very effective as an ingredient for plants that like sogged conditions and all South Africans that like wet feet can be grown very well in a mix containing vermiculite as once it receives a good soaking will remain water retentive for long.

Perlite is a lot more lasting without deteriorating but this is again another case of being very careful with excess watering.

[David Nicholson]

Giles, I have used Perlite as a topping for Primula seeds in the past and got very good germination followed by pretty effective damping off You may need to keep a very careful eye on them.

[Darren]

Giles,

David is right - damping off can be a problem. As Alberto rightly points out, the stuff does hold a lot of water! I try to sterilise the compost before sowing by pouring a kettle of boiling water through it. Then water only with tapwater until the seedlings are established. I still find it the best covering for these seeds though - my pot of Primula flaccida from SRGC seed looks very much like your picture!

Glad you are having success with it also 

[ChrisB]

I use vermiculite mixed in equal parts with silver sand to put cuttings into to root.  It has, in the past, been particularly successful with diascias, but I no longer have the collection any more.  The great thing about this mix is that you can lift the newly rooted cuttings without any soil and post them off if you need to knowing you are not spreading anything unpleasant by mistake.  For easy to root things like diascias, it takes about 3 weeks for most to develop roots, while other things can take longer. The cuttings do very well once potted on too.  I have no scientific knowledge, but I think the sand makes the roots that develop a bit more robust than they are when cuttings are rooted in water.  The vermiculite holds the water nicely so mixed together it just works.  I've rooted loads of things in it, not just diascias, but even woody things like daphnes or box and suchlike.

[David Pilling]

I'll probably regret saying this... since I started using B&Q cutting and seed compost (cut and sow) a few years back I've seen nothing damp off. Be interesting to know what the magic ingredient is.

[ChrisB]

That's very interesting David, might try some next time I'm near B&Q....

[JPB]

It is not clear to me if vermiculite is inert. Does it decompose in some way? I have not seen it decomposting

From the messages I read that you use it for seed/cutting mix. Do you use it for potting mix in mature plants, i.e. for repotting? What are your experiences?I use vermiculite not only for my seed/cutting mix, but also in the mix of mature plants (10-20%).

[ChrisB]

Hi Hans,

I used to use it in composts, but I was needing to keep the soil moist for my diascias, but nowadays and not doing the same  volume of diascias, I tend to use perlite which helps promote drainage rather than vermiculite which does almost the opposite.  It is very useful to root cuttings, especially softwood or fleshy things like diascias as it keeps in the moisture whilst the sand helps the resulting roots to 'toughen' up some during the process.  It also means there is no soil at all on the cuttings prior to potting them on, and when I had to post off cuttings hither and thither, it meant I wasn't sending anything nasty in soil to the recipients.  But as I say, I no longer do this as I've given up the diascia collection.  I don't think vermiculite decomposes, isn't it some sort of rock that's been blown up?  When I turn soil where I've thrown out pots containing vermiculite, I can still see it in the soil years later and I used to use a great deal of it.

[JPB]

Chris, your sand/vermiculite 1/1 is a nice recepe for cuttings. I'll try is soon. Up to now I use cutting potmix with perlite, but still have some losts from rotting. Pure vermiculite is not working for cutting, I have found out.

In many plants I use good turf-based potting soil with 1/4 vermiculite, 1/4 perlite and some sieved loamy clay. I don't have any experience with 'soggyness' of the vermiculite up to now.

The point is, you can always change the watering-, light-, and temperature-regimes easily, but changing soil mix is more work and disturbing roots. hence my quest for a perfect potting soil

Cheers, Hans

[David Pilling]

Presumably if you use a pure inert mixture like sand + vermiulite you add plant food?

I once tried growing lily seeds in many different mixtures, ranging from pure sand to pure peat, including vermiculite, perlite and grit, I was fed up with fungus gnat larvae and I thought they might not like mixtures with no peat. The lilies grew in all of them, but I soaked the pots in Wilko Wonder Grow regularly.

At the moment I'm trying silica gel cat litter, which looks fantastically drying...