Slow seedling growth- is media to blame?

[Shane]

I planted my first (ever) batch of seeds in March. I used sand as the potting medium (I found a guide on the internet that could be politely called unorthodox). The growth has really slowed down, and I'm considering transplanting them

I see three main issues with sand. First, it has this tendency to slowly dry out (even in a closed container), and is difficult to water without flooding. It doesn't have any organic matter to provide nutrients to the plants. It also tends to get compacted, providing less than ideal conditions for root growth

I planted a second batch of seeds in a 90/10 mix of succulent potting media (50/50 potting soil and small gravel) and sand. I haven't had any issues with this soil so far

I'm curious to hear others' thoughts on this. Would transplanting really help or does growth just slow down a lot after the first month or two?

[Niko13]

Your xp only confirms that seedling can't grow in 100% inorganic media. It needs organic part to provide nutrients. They can germinate in sand, but not grow in it.
I've tried to grow seedlins in pure perlite in a small cup just for experiment. They germinated, but then started dying and I saved 1 by transplanting it.

[keith]

Pure sand only I don't think I have ever tried that and you probably need to fertilize it or transplant. I add washed sand to soil to germinate seeds because my normal mix is too porous and seedlings have small roots.

[dwood5513]

Did an experiment, three batches of ferocactus seedlings:

100% organic (pure potting soil), had to put coarse sand on top to prevent massive fungal attacks
50% organic/50% inorganic (potting soil/pumice/turface/napa floor dry/sand)
100% inorganic. (coarse sand)

Not surprisingly 100% inorganic was the worst, low germination, and most looked stressed and/or dried up.
Best was surprising, 100% organic had highest germination and grew best at the initial phase.
Most damped off though because of the excessive moisture involved.
That taught me that going probably 50/50 or 60(organic)/40 with coarse topsand was better than what I was doing which was like 8:2, 7:3.
BUt I was very surprised how well pure soil did. I was thinking of adjusting to like 75/25 (organic/inorganic) and really sterilizing the soil to get better growth rates (I guess thats kind of what growing nurseries do).

[dwood5513]

Did an experiment, three batches of ferocactus seedlings:

100% organic (pure potting soil), had to put coarse sand on top to prevent massive fungal attacks
50% organic/50% inorganic (potting soil/pumice/turface/napa floor dry/sand)
100% inorganic. (coarse sand)

Not surprisingly 100% inorganic was the worst, low germination, and most looked stressed and/or dried up.
Best was surprising, 100% organic had highest germination and grew best at the initial phase.
Most damped off though because of the excessive moisture involved.
That taught me that going probably 50/50 or 60(organic)/40 with coarse topsand was better than what I was doing which was like 8:2, 7:3.
BUt I was very surprised how well pure soil did. I was thinking of adjusting to like 75/25 (organic/inorganic) and really sterilizing the soil to get better growth rates (I guess thats kind of what growing nurseries do).

I should also add that this was just with easy species like ferocactus. I've been growing blossfeldia in pure inorganic and it seems fine, albeit slow.

[mmcavall]

Considering it is your first (ever) batch, you may be disapointed by the slow growth, but cacti seedlings are really slow.

Your mix may not be the best (I dont like using sand), but you cannot expect that cacti seedlings grow fast.

As for 100% inorganic mixes, in my experience, they are suitable for many cacti species during the first six months, at least. My higher success rate has been with pure grit, with absolutely no soil added.

[Pereskiopsisdotcom]

Most sand particles have a tendency to clump and that could prevent roots from moving freely or water from even penetrating the desired area. Like others mentioned, I too was convinced a pure inorganic mix would be the best. My experience was that it was the worst germination rate and was incredibly difficult to keep seedlings going once germinated. They were more susceptible to sunburn, needed more watering and looked leggy. And I wasted a lot of time and a lot of money on seeds with that method.

In the last few years, I have switched to a mix that is about 50% coconut coir and 50% grit of various kinds (granite, fired clay, no sand). Now, make no mistake there are no nutrients to be gained from coconut coir. I supplement with seaweed and fish fertilizer after about one month. Everything looks vibrant and I have little damping off. I do have to contend with algae on the top of the grit but that's normally not harmful at all.

[Shane]

Thanks for all the responses. I transplanted my Astrophytum late last week and they all seem to have survived. I think transplanting is the right long term solution to the problems the sand has been causing (lack of nutrients, too densely packed for good root growth, drying too quickly). I should have mentioned this before, but I grew only easy to grow kinds of seed, i.e. nothing that needs to be grown in sand

50 down, 250 to go

[7george]

Would transplanting really help or does growth just slow down a lot after the first month or two?

No, growth doesn't slow down after first months (but you should keep days long and temperatures high). And transplanting really helps to keep it intensive. Especially if seedlings are densely packed and the germinating soil is not fertile and aerated enough. Then I plant them in a common tray (container) in alternating rows in about two diameters from one to another. When growing seedlings start touching each other again would be a time for the next thinning.

[Shane]

In the month since posting, the different growth rates of my seedlings grown in sand and mixed soil has become striking. The cacti sown in a mixed soil in July are now as big as those started in sand in March. Also the Astros have grown noticeably in the few weeks since I transplanted them