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What the best soil mix


bigphil1984

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For all cacti and succulents I use:

65% river sand

10% perlite

5% peat

10% potting soil

10%  compost soil

These aren't measured exactly, I just mix up the whole lot in a wheelbarrow until I have it well blended looking like dark sand. Some times I add a small bag of vermiculite and a generous helping of organic bonemeal, if I have it at hand.

Finally I add a layer of OsmoCote after the plant has gone into the container. The peat and soil in the mix absorb the nutrients released by the OsmoCote to keep it available to the plant for longer.

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For all cacti and succulents I use:
65% river sand
10% perlite
5% peat
10% potting soil
10%  compost soil
These aren't measured exactly, I just mix up the whole lot in a wheelbarrow until I have it well blended looking like dark sand. Some times I add a small bag of vermiculite and a generous helping of organic bonemeal, if I have it at hand.
Finally I add a layer of OsmoCote after the plant has gone into the container. The peat and soil in the mix absorb the nutrients released by the OsmoCote to keep it available to the plant for longer.
Thanks JuanP, I've got some peat moss, ready mixed carnivorous plant compost, silica sand, potting grit and perlite! Which would you use out of these some people stay away from peat for cactus is this right?

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In a substantial quantity peat would be very bad for succulents and cacti as it retains lots of moisture.
But as 5% of the mix that has been mixed in very well, I find it does offer a benefit.
Ok thanks, I'll use 5% peat. I was planning on starting cactus and bamboo off indoors in a grow tent with a 300 watt led, till they get established.

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Well, you could do two experimental batches of 5 seeds each, and see how the ones in the grow tent fare compared to those outside?

Getting them to germinate is the challenge, a container with high humidity placed in the sun worked best for me, gave them moisture, light and heat to sprout.

From there it's a slow waiting game as they don't grow much from there on... But that could be because I started them in the mid of winter.

Now that it's turning into Spring here, everything has been going into grow mode again.

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Interesting advice from Juan but I think it might be useful to bear in mind that the climates in the UK and South Africa are very different.  In the UK we have to contend with cool wet weather and (for cacti) a long dormancy period from roughly October to April.  We can only dream of the average temperatures that Juan might see in Pretoria and this will be a significant factor when it comes to growing plants like cacti and other succulents.

One thing these plants don't like is being wet and cold so (for our climate) it's generally considered best to have a very open and free draining compost, such as by adding grit or other similar materials.  I find that sand has the opposite effect and in fact binds the mix together so that it retains water rather than lets it pass through.  I do use small amounts of sand on occasions but 65% seems rather a lot.  As Juan rightly says, peat in substantial quantities retains too much moisture (and fungus gnats seem to love it too) so best to aim for a lower percentage.  Here cacti growers generally use a John Innes type compost (No 2 or 3) as their base and then add any of grit, perlite, pumice or cat litter etc to open the mix up so that it becomes open and free draining.  John Innes compost is supposed to have peat in it but these days who knows.  Possible proportions to consider would be John Innes No 3/Grit split 70/30 or 60/40 but it is hard to generalise even within the UK as what works in the Southern counties may not be right for us folks further North.  Best to experiment and find what works for you but I'd certainly start off with a mix with plenty of grit and not much of either sand or added peat.

Similarly growing cacti seedlings outdoors in SA may well be possible but here in the UK I doubt very much that it would be a huge success (might be OK down south).  For me it's a bit late in the year for setting cacti seeds but they may be OK in your grow tent with extra light.

Good luck and don't forget to let us know how you get on.

 

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Interesting advice from Juan but I think it might be useful to bear in mind that the climates in the UK and South Africa are very different.  In the UK we have to contend with cool wet weather and (for cacti) a long dormancy period from roughly October to April.  We can only dream of the average temperatures that Juan might see in Pretoria and this will be a significant factor when it comes to growing plants like cacti and other succulents.
One thing these plants don't like is being wet and cold so (for our climate) it's generally considered best to have a very open and free draining compost, such as by adding grit or other similar materials.  I find that sand has the opposite effect and in fact binds the mix together so that it retains water rather than lets it pass through.  I do use small amounts of sand on occasions but 65% seems rather a lot.  As Juan rightly says, peat in substantial quantities retains too much moisture (and fungus gnats seem to love it too) so best to aim for a lower percentage.  Here cacti growers generally use a John Innes type compost (No 2 or 3) as their base and then add any of grit, perlite, pumice or cat litter etc to open the mix up so that it becomes open and free draining.  John Innes compost is supposed to have peat in it but these days who knows.  Possible proportions to consider would be John Innes No 3/Grit split 70/30 or 60/40 but it is hard to generalise even within the UK as what works in the Southern counties may not be right for us folks further North.  Best to experiment and find what works for you but I'd certainly start off with a mix with plenty of grit and not much of either sand or added peat.
Similarly growing cacti seedlings outdoors in SA may well be possible but here in the UK I doubt very much that it would be a huge success (might be OK down south).  For me it's a bit late in the year for setting cacti seeds but they may be OK in your grow tent with extra light.
Good luck and don't forget to let us know how you get on.
 
Thanks gaz mate, I'll definitely do them in the tent since up here north, you can't rely on the weather being nice for long lol. My other plants don't mind it but I guess the cactus would. So would you sow seeds in gritty mix or is that just for established plants? I defo keep you all updated, I'll take some pics when I've set up! [emoji6]

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That is true @Gaz our winter was quite mild this year. Only on two occasions we dipped to 0°C with the average coldest temps being around 5°C lows. The big difference would be we have a dry winter, so you control what moisture gets to what plants.

The river sand I use has no presorting and ranges from 1mm to 5mm particles, the finer stuff tends to wash out quickly with a few waterings. Perlite added to this also makes it much more porous.

One thing I have noticed though, is mixing it all together and letting it dry out a bit, mixing it up with a shovel again, then adding it to the intended pots, ensures an even airier mix that drains fast consistently. If I use a freshly mixed batch that was moist to begin with, it compacts and water drains slower.

Also in my experience, it's best not to compact the mix into the pot, but rather wet it down, let it settle, then top up with more mix. This way it all settles into place naturally, and so far I can see robust root growth from doing this (my cuttings are in clear plastic pots to monitor root progress)

Maybe for your wet weather, pumice would also be a good addition? Much bigger particles than perlite, a bit heavier too, and very porous. 

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5 hours ago, bigphil1984 said:

So would you sow seeds in gritty mix or is that just for established plants? I defo keep you all updated, I'll take some pics when I've set up! emoji6.png

With all the garbage they put in them these days anything starting with John Innes 2 or 3 type compost as a base will be too coarse for seed growing, unless you're talking about runner beans.  You could start with a seed compost and add something to open it up (coarse sand, small grade grit etc.).

It's just a thought but have you thought about joining the British Cactus Society forum?  There's a lot of people over there with decades of experience in growing cacti and they would be able to answer all of your questions better than me plus there are years worth of archived posts to search about any cacti subject.  You can join the society as well, if you're so inclined, and benefit from quarterly magazines, seed lists, plant sales, cactus shows, branch meetings etc.  I'm not on commission, honest, but it's worth considering if you want to start growing cacti.

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With all the garbage they put in them these days anything starting with John Innes 2 or 3 type compost as a base will be too coarse for seed growing, unless you're talking about runner beans.  You could start with a seed compost and add something to open it up (coarse sand, small grade grit etc.).
It's just a thought but have you thought about joining the British Cactus Society forum?  There's a lot of people over there with decades of experience in growing cacti and they would be able to answer all of your questions better than me plus there are years worth of archived posts to search about any cacti subject.  You can join the society as well, if you're so inclined, and benefit from quarterly magazines, seed lists, plant sales, cactus shows, branch meetings etc.  I'm not on commission, honest, but it's worth considering if you want to start growing cacti.
I'll join it [emoji38] thanks gaz. But I've just made my mix for them it looks ok I think?03d635e75ece144075177695f5e6674e.jpg9f27e678ef1b861caa5f25a44acefe71.jpg

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6 minutes ago, bigphil1984 said:

2 parts potting compost, 1 and a half part pure white silica sand, 1 part perlite, and one part potting grit.

looks good to me :tu:

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7 minutes ago, bigphil1984 said:

Was going to scarify seeds or do you not think they need it?

I haven't heard there's a need (assuming we're still talking cacti) but I have to confess my results at growing them from seed has been dismal, I seem to have better luck with Lithops, mesembryanthemums and Haworthia. 

Some of those guys over at the cactus and succulent forum recommend growing cactus seedlings far wetter than you would expect and talk about something called the "baggie method", might be worth going over there and asking or searching about it.  The idea is you seal the seed tray in a zip-lock bag or similar and keep very wet until the seedlings are quite big.  Hasn't worked for me yet to be honest but they swear by it.

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7 hours ago, JuanP said:

The river sand I use has no presorting and ranges from 1mm to 5mm particles, the finer stuff tends to wash out quickly with a few waterings. Perlite added to this also makes it much more porous.

One thing I have noticed though, is mixing it all together and letting it dry out a bit, mixing it up with a shovel again, then adding it to the intended pots, ensures an even airier mix that drains fast consistently. If I use a freshly mixed batch that was moist to begin with, it compacts and water drains slower.

Maybe for your wet weather, pumice would also be a good addition? Much bigger particles than perlite, a bit heavier too, and very porous. 

Hi @JuanP, your river sand does sound interesting.  I don't know if we have anything quite like that here.  Pumice is also not that easy to source except in small quantities such as from Bonsai suppliers. I've found it needs very thorough washing to get rid of the fines and isn't really economically viable here.  A lot of people here use cat litter made from clay as an alternative to perlite, it's a bit like pumice too.

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4 hours ago, bigphil1984 said:

My sealed tray emoji6.png9ab080565ea00d982bc7e861fe2d4cb2.jpg

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I would like to hear the other's experience from different locations, but from my own experience, I ventilate all seed germination containers with two 4mm holes in the lids, for larger containers I make four holes.

I get less algae, the germinated plants grow better, and humidity still stays high, with a misting every couple of days to keep the soil moisture up.

This applies to all seeds I germinate, from Crassula all the way to Drosera with anything imaginable inbetween.

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Many years ago, when I started growing cactus seeds, I used a similar system, although it was in a SW facing conservatory, here in SE England. I found the levels of algae irritating, and there was a certain amount of mortality associated with the dampness and humidity.

In recent times, I just use a fine soil mix, close to what I can discover about their native soil, sow the seeds on the surface, and cover them with very fine grit (1 - 2mm, sifted from sand) just enough to make the soil invisible. Then I stand the pot in water, and leave it in an appropriate spot in the conservatory. I only do this in the warm months of the year, spring and early summer being best. I keep the pot topped up with water until most/all seeds have germinated.

I've found using this method I get between zero and almost zero algae growth, and no mortalities from humidity. Germination has always been good.

This was for seeds up to Astrophytum size.

Karsty.

Edited by Karsty
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