Heey

So, about an half-year ago I got to the conclusion that store-bought cactus soil alone was not that good for the plants.

The thread "Doubting the soil I've been using" in Cactus and Succulents forum

So I ended up mixing some scraps of gravel and coarse sand I had around the house to repot a couple of cacti, but left the ones I already had in the store-bought soil.

In the meantime, my cactus and succulent collection doubled, and now that spring is around the corner, I wanted to get soil mixing right.

This mix will be used in indoor cacti, and I will most definitely use:

- Store-bought Cactus Soil Mix (compost and peat)

- Coarse Sand (might use aquarium sand, washed, have a lot of that lying around)

- Grit

Now comes the ones I'm not so sure about:

- Might add to/replace Grit with Perlite, Expanded Perlite (might even be the same thing), Pumice or Vermiculite. Not sure what are the benefits each one of these might bring to the mix

- Might add another organic ingredient, like bark or coconut peat (about this last, I've read in some places that it works wonders, in others, that it should never be used )

Would love to know your opinion on these! Thanks in advance!

My advice would be to be consistent with the mix, as much as you can, once you settle on something you like. That will simplify the watering down the road.

I would think a 50-50 mix of your organic soil and sand, grit or perlite/pumice/equivalent would be helpful for most cacti. Pass the sand over a window screen to remove the fines if necessary. I like pumice for the aggregate partly because it's a little heavier than perlite, and especially because it doesn't come with the nasty dust that perlite does (wear a face mask so you don't inhale the nasty perlite dust if you go that route). I don't think vermiculite will be particularly helpful as it tends to hold on to water, like fine sand does. I don't know if pumice or perlite would accomplish anything that sharp grit in the right size range can do, but I stick with what I have always used (pumice). My product ranges from 2.5mm to 6mm in size.

My mix is 50% pumice, 25% potting soil (mostly compost), 25% cocofiber. The cocofiber has two advantages over the potting soil. It takes much longer to break down into dust, so has a longer lifespan in the soil (I don't like to repot my plants unless they need more space). And it absorbs an obscene amount of water, like 5 times its dry weight. In that sense it functions like peat, though it might repel water a bit less when dry, and it's eco-friendly because it's a renewable resource (basically a waste product). Use the finely ground product for most small cacti (there's also an extra chunky size available for use as mulch).

I use a lot of gravel in my plants. Yes, contrary to popular belief, it works

This was planted in almost pure gravel, with some of its own soil mixed in..accidentally and a very small amount
I also have used perlite, grit, baked clay, leca balls, crushed brick,
I found that the gravel+ perlite mix works best, sometimes with about less than 25 % soil for more needy plants.
I grow cacti in less than ideal conditions, and the new soil works 97% of the time...
Also, expanded perlite is regular perlite thats available...
Perlite is a grey rock that you get when obsidian decays due to groundwater or something...and its baked to make the commercial white perlite///

I use about the same mix as Baja, about 50/50 cactus potting soil (just the inexpensive stuff) and pumice. I recommend pumice or other coarse grit like crushed lava rock over perlite -- partly because of perlite's nasty dust, as Baja mentioned, and partly because it floats and tends to migrate to the top of the pot over time. Vermiculite isn't necessary; it increases water retention and your potting soil, compost, and/or cocofiber retain enough as they are.

Always remember that you need to adjust any formula for your growing conditions and the type of plant. Extremists like lithops need more grit than average; tropicals like orchid cacti need less. Succulents that are outside and getting rain need better drainage than ones that are inside only. And so on.

Thanks everyone. I feel like I have a good notion of the kind of mix I should have.

I should to end up with a 50-50 organic and inorganic mix for now, as most of you. Probably going to use compost, peat, coir, coarse sand and perlite or pea gravel (was leaning towards pumice, but it is proving quite difficult to find here in Portugal ).

@Baja_Costero Sounds like coconut peat is a safe bet then! I was afraid to use it, as I've read that because it absorbs that much water, it keeps it from actually leaving the pot, and might encourage rotting.

@skopjecollection Wow it's amazing how your cacti do so well in that soil, and that bloom is just gorgeous! (btw, what happens with the other 3%? )

Wallknocker said:Thanks everyone. I feel like I have a good notion of the kind of mix I should have.

I should to end up with a 50-50 organic and inorganic mix for now, as most of you. Probably going to use compost, peat, coir, coarse sand and perlite or pea gravel (was leaning towards pumice, but it is proving quite difficult to find here in Portugal ).

@Baja_Costero Sounds like coconut peat is a safe bet then! I was afraid to use it, as I've read that because it absorbs that much water, it keeps it from actually leaving the pot, and might encourage rotting.

@skopjecollection Wow it's amazing how your cacti do so well in that soil, and that bloom is just gorgeous! (btw, what happens with the other 3%? )

Ive had some failures...
Repotted some the wrong way, some were damaged to begin with....some...i soaked in water for too long... some were just unlucky..
Nothing is foolproof....

[quote="Baja_Costero"]
and it's eco-friendly because it's a renewable resource (basically a waste product).

There is no proof that coir is anymore environmentally friendly. It is quite a dirty industry. The coco-coir sales pitch was that it was a waste byproduct. This was nothing more than propaganda. Coco-coir was used by farmers for many many years. They applied it to their coconut plantations and other farms as a soil conditioner. It was not until westerns wanted it that it became unaffordable for farmers to use. At that point it became a waste product. Now those farmers rely on synthetic fertiliser.

The working conditions and wages are not on par for the amount western are paying. Some of the cheaper coco-peat has been produced with some dirty chemicals. These chemical put local communities in harms way. Always 3rd world countries. Something we don't see, so we really know very little about. I can guarantee it is not as regulated as peat harvesting is.

Tropical peat forest, home to rhino and tigers are being burned to plant palm trees, both Coconut and Palm Oil palm trees. These forest can never be replaced.

It also has to be shipped half-way across the world.

At best peat and coco-peat are equal for there environmental footprint.

Peat is actually cleaner than you think. Before harvest a new bog, they harvest the plants and plant them in the last bog they harvested. They never harvest to the bottom. They also use tissue cultures to grow plants to replant the bogs. It takes about 10 years for a bog to recover from being harvested.

There is lots of federal funding both in the US and in Canada for wetland restoration projects. These farmers are able to tap into these funds to do all this work without increasing the price of peat.

Unlike Ireland and Finland we are not burning our peat. This means the carbon trapped in peat will remain in the peat as long as you are using it for horticultural reasons. Many of the statistics used to sell coco-peat are based on research done in these countries and in England where it was used for fuel for many years.

The dirtiest part of this industry is the amount of fuel it takes to harvest a bog. It is more than you would expect. This is carbon that is being released into the air.

Please don't get me wrong, I don't think peat is the greatest thing in the world. I actually offset my peat usage with ground bark. There is more ground bark in my succulent blend then there is peat. I am not saying the lumber industry is clean, but bark is the true waste-byproduct. Trees are not harvested for their bark, bark is something the industry needs to get rid of.

I bought into the whole coconut coir is more environmentally friendly for many years. It was an eye opening experience when I learned the truths.

@baja
why do you think cocofiber is good for absorbing water but vermiculite is bad? Is it because one has nutrients and the other is inert? I don't use either at the moment, just interested in what you have experienced
Steve

another thing that confuses me is why nursery plants do so well is dense soil?

Often plants will seem to initially go backwards when i pot them into my grittier mix. Maybe it is just the plants adjusting ? I can't believe nurseries are re potting plants , so does it have something to do with other environmental conditions? why do these plant grow so well for the sellers in plastic pots and poor soil?
Steve

I guess the thing I look for is soil that can absorb water but does not necessarily retain it. The cocofiber is good in this respect, the vermiculite not so much. I know people who put vermiculite in their mix and think it's great, so I'm sure it can be made to work if you are attentive to soil moisture.

As for the second question, a pretty wide variety of soil types can be made to work if you get the water and light right. With the denser soil types you have to exercise restraint with watering. They work great for some plants. In my mind the addition of pumice (or whatever kind of grit you prefer) is all about making the watering easier, since it facilitates rapid drying (given good exposure) and lowers the risk of the soil staying wet at depth persistently. Presumably growers who use less grit in their mix have fine tuned the watering to compensate.

@wallknocker so my mix for all my cacti, succulents, and caudiciforms is lava rock, peat\perlite mix. I very the percentages of lava to peat depending on plant. But it's usually about 60/40. I have some stuff that is potted in as high as 70/30. It has worked very well for me over the last almost decade of growing in it. I come from a bonsai background so I prefer to grow in higher percentages of stone aggregate and water more often. I never have any rot problems this way, never had any moisture related deaths this way. I feel like I get steadier, better growth in high percentages of lava.