Experiences with pumice and red or black lava stone to sow seeds

[yonnoy]

Do you have experiences using pumice, red or black lava stone to sow cactus or succulents seeds?

[MikeInOz]

I use very fine red lava (scoria) as a thin top dressing to sow my seeds on. They germinate well because the particles hold a good amount of moisture and seem to encourage root hairs to form. Pumice is also good but I find all the light coloured materials to encourage the growth of algae. Make sure you wash the scoria well before using it. Also, some samples of lava have been shown to be toxic. If in doubt, you can do the radish seed test - put some scoria in a pot and plant some radish seeds. After a week or 2, empty out the pot and check the roots. If they have nice clean, white tips, (use a magnifying glass) the material is fine. If they have brown tips, not so good or downright disastrous.

[greenknight]

I use a blend of 3 parts pumice and one part good quality potting soil, pasteurized in a microwave. It does tend to grow algae, but the algae is harmless to the seedlings. Cactus seedlings make strong root growth in this mix.

[keith]

I use 1/3 sand and 1/3 sandy soil from the desert and 1/3 dry stall pumice for mesembs , same for cactus but maybe less sandy soil for cactus . lava rock I have used with mixed results same with turface. Store bought soil also not very good results.

Where you get the sandy soil is pretty important and how to test if its any good IDK ? trial and error I guess. With cactus seedlings if they mold up and die right away its no good . I don't microwave the soil.

[jerrytheplater]

Also, some samples of lava have been shown to be toxic. If in doubt, you can do the radish seed test - put some scoria in a pot and plant some radish seeds. After a week or 2, empty out the pot and check the roots. If they have nice clean, white tips, (use a magnifying glass) the material is fine. If they have brown tips, not so good or downright disastrous.

I like that radish test. Good idea.

[MikeInOz]

Also, some samples of lava have been shown to be toxic. If in doubt, you can do the radish seed test - put some scoria in a pot and plant some radish seeds. After a week or 2, empty out the pot and check the roots. If they have nice clean, white tips, (use a magnifying glass) the material is fine. If they have brown tips, not so good or downright disastrous.

I like that radish test. Good idea.

Yes it's very simple and pretty much fool proof.