What's the point of adding inorganic medium to seed sowing soil when using the baggy method?

[Mas_]

Hi, sorry if this is a stupid question but I'm quite to new to all this. I was wondering why people add things like pumice, grit or scoria to their soil when sowing seeds using the baggy method. Surely the point is to keep the soil moist and wet, so why add things that would improve drainage when your trying to keep the soil wet? Do the pumice and scoria provide things other then drainage- for example nutrition? Also, i'm planning to sow some seeds and have a 44% peat soil (JI number 2) and a peat free soil (cactus focus). Which one is better to use for sowing seeds and which one should I reserve for adult plants? I know a lot of people advise against using peat since it is hard to re-wet but that won't be problem for me since the soil will be constantly wet in the bag. Or should I just use the peat free since it's better to avoid using peat all together. Also, would using both scoria and pumice in my seed sowing mix be overkill? Thanks

[samhain]

When coming out of the baggie there isn’t a need to repot for some time. Peat and other poor soil attributes can show problems at that point.

[Mas_]

When coming out of the baggie there isn’t a need to repot for some time. Peat can show its problems at that point.

I was always under the impression that you should transplant the seedlings once you take them out of the bag. I have some seedlings that are nearly a year old and i'm slowly acclimatising them to outside the bag. They are getting slightly too big for their pot- should I leave them be or should I transplant them? They were sown in a commercial cacti mix and sand and i'm planning to transplant them into the mix I use for all my adult plants which I much more inorganic.

[samhain]

If they are crowded time to repot. Often that’s not the case when coming out of the bag, will vary.

[One Windowsill]

The point of adding "drainage" is to allow oxygen to get to the developing seed, the roots especially. The "drainage" allows lots of little air pockets around the seedling, promoting fast oxygenation of the water in the substrate. The substrate should only be damp not sopping wet.

It is important to sterilise the soil before sowing seeds. I think most people microwave while wet until it reaches 70°C or so.

[Jangaudi]

fine pumice, or coarse sand keeps the soil loose also, it does not start sticking together, and all the air pockets enable good and fast root development imo

[Mas_]

fine pumice, or coarse sand keeps the soil loose also, it does not start sticking together, and all the air pockets enable good and fast root development imo

Thanks so much for the help. I don't have any sand, but when I was washing my pumice and lava rock with a sieve, I noticed a ton of fine particles almost sand like, being washed out. It was like tiny tiny granules of crushed up lava rock and pumice. I was wondering could I wash my lava rock, but keep the stuff that gets washed out and add it to my mix or no?

[Mas_]

The point of adding "drainage" is to allow oxygen to get to the developing seed, the roots especially. The "drainage" allows lots of little air pockets around the seedling, promoting fast oxygenation of the water in the substrate. The substrate should only be damp not sopping wet.

It is important to sterilise the soil before sowing seeds. I think most people microwave while wet until it reaches 70°C or so.

I see, that explains a lot. Does the inorganic stuff like lava rock and pumice also supply nutrients or is the sole purpose drainage? Would it be okay for me to use both in my sowing mix or would that be too much? I have heard that they could give out too much nutrients, making the soil toxic but i'm not sure if there's any truth to that.

[greenknight]

Lava and pumice are used for drainage - the solubility of the minerals they contain is very low, they're not going to release a significant amount. When rock is added to soil as a mineral source, it's ground very fine, like flour, and it's still very slow-acting.

Pumice, being porous, absorbs a fair amount of water. Lava rock or other hard rock is not absorbent, and is added to cactus mix to reduce the amount of water it holds, which is especially desirable in regions where humidity is high during the growing season. Using some lava rock in your starting mix won't hurt anything, but the seedlings will need water sooner.

[anttisepp]

I think it's bette to sow in pure sand, later adding a small amount of liquid fertilizer, much less fungus problems. IMHO
If you'll replant small seedlings every 2-3 month they'ii grow much faster. Recommend.

[mmcavall]

fine pumice, or coarse sand keeps the soil loose also, it does not start sticking together, and all the air pockets enable good and fast root development imo

Thanks so much for the help. I don't have any sand, but when I was washing my pumice and lava rock with a sieve, I noticed a ton of fine particles almost sand like, being washed out. It was like tiny tiny granules of crushed up lava rock and pumice. I was wondering could I wash my lava rock, but keep the stuff that gets washed out and add it to my mix or no?

I use to sieve all inorganic components of my mix and I throw away the very fine particles. They are not good for the roots, since they clog the pores of the mix. However, the "coarse sand sized particles" are useful to the sowing mix..only the dusty like particles are thrown away

[keith]

I was wondering could I wash my lava rock, but keep the stuff that gets washed out and add it to my mix or no?"

Small sized particles I find useful for seedlings especially tiny seeds. You're right you could use it as a sand for small seedlings.

I use sand but I have access to mountains of it.