[TerryB]

Which is the best, Perlite or Vermiculite, to mix with compost to raise seeds?

[Paul Plots]

I'm not much help (have used vermiculite) but I had to look this up:

What's the difference between perlite and vermiculite?

Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently. It is an industrial mineral and a commercial product useful for its light weight after processing.

Vermiculite is a natural clay mineral that expands with the application of heat. The expansion process is called exfoliation and it is routinely accomplished in purpose-designed commercial furnaces. Vermiculite is formed by weathering or hydrothermal alteration of biotite or phlogopite. Large commercial vermiculite mines currently exist in South Africa, China, and Brazil.
Source(s):
Professional Geologist
Wikipedia

[Kristen]

I use seed sowing compost (John Innes formulation) and I don't add anything. I cover the seeds with Vermiculite.

Most vegetable seeds, particularly the larger ones, are not going to be too fussed about what sort of compost (i.e. something out of a bag, rather than soil out of the garden) they are grown on, and covering the seeds with Vermiculite is just personal preference - although if you are growing any slow-germinating-seeds I definitely recommend it to reduce the amount of green algae that would otherwise grow on the surface.

I add Perlite to compost to make it more open / free draining, for things like cuttings. For just growing on I use multi-purpose compost straight out of the bag.

[savbo]

is it basically that perlite improves aeration and speeds drainage, while vermiculite improves aeration but holds water and nutrients?

I sometimes use vermiculite on the surface of compost to cover seeds that need light to stop them drying. wouldn't do that with perlite!

[Paul Plots]

I use seed sowing compost (John Innes formulation) and I don't add anything. I cover the seeds with Vermiculite.

Most vegetable seeds, particularly the larger ones, are not going to be too fussed about what sort of compost (i.e. something out of a bag, rather than soil out of the garden) they are grown on, and covering the seeds with Vermiculite is just personal preference - although if you are growing any slow-germinating-seeds I definitely recommend it to reduce the amount of green algae that would otherwise grow on the surface.

That's what I used vermiculite for....covering very tiny and expensive seeds. I don't use it for veg seeds at all.  

[Paul Plots]

is it basically that perlite improves aeration and speeds drainage, while vermiculite improves aeration but holds water and nutrients?

I sometimes use vermiculite on the surface of compost to cover seeds that need light to stop them drying. wouldn't do that with perlite!

Not the foggiest!

Terry, what makes you want to use either of them?

[bigben]

I keep seeing people on Gardeners world etc using this stuff. What is the advantage of this over just a little more compost?

[Kristen]

is it basically that perlite improves aeration and speeds drainage, while vermiculite improves aeration but holds water and nutrients?

Perlite holds water too - best to add water to the bag before taking any out as its very dusty otherwise, but it gains a lot of weight as water is added - thus retains water

[Kristen]

I keep seeing people on Gardeners world etc using this stuff. What is the advantage of this over just a little more compost?

I use it on seed that requires light to germinate - as its fairly transparent (well, compared to sieving some soil over the seeds!) - dunno if it is transparent enough? but I get near to 100% germination on Petunia seed for example.

Its also very light - so easier for seeds to push through.

But that's just my opinion, not facts that I have read per se.

[Paul Plots]

I keep seeing people on Gardeners world etc using this stuff. What is the advantage of this over just a little more compost?

As someone has said here... it is less likely to go green than compost, tends to be lighter and easier for small seedlings to push up through into the light. Good for small seeds that take an age to germinate.

I've used it on occasions for small flower seeds where I have only a few of them and they cost a packet but other than that.... Preferences and personal choices maybe?

Sorry Kristen.. I posted at about the same time as you. Didn't mean to repeat what you had said. Great minds think alike? 

[Kristen]

Preferences and personal choices maybe?

+ Habit - in my case - A small bag lasts me several seasons, but its a non-renewable resource, so I ought really to moderate my habit ...

[bigben]

I might give it a go. It probably also makes it easy to see if you have covered everything as it will be a different colour to the compost?

[Paul Plots]

Preferences and personal choices maybe?

+ Habit - in my case - A small bag lasts me several seasons, but its a non-renewable resource, so I ought really to moderate my habit ...

It'll go back into the soil from whence it originally came and you aren't using tons of it.
I wouldn't feel guilty about one bag once every few years. There's a great deal more waste around us that no one seems to worry about. 

[Kristen]

I might give it a go. It probably also makes it easy to see if you have covered everything as it will be a different colour to the compost?

Yes, the fact that it is a different colour makes it easy to see that you have an even covering.

[TerryB]

Thanks for all the comments.
I think I will try the Vermiculite, as I do have proplems with Green Algea on multi compost and its also recommended when repotting the OH Disa Orchid.