Soil requirements for cacti.
In general, cactus soil is designed to mimic a cactus' natural environment, which is typically dry and nutrient poor.
But just sticking your cactus in a pot full of sand isn't a recipe for a healthy plant.
The problem with generic potting mixes for cacti is that they not suitable for each type of cactus. If you want to potentially have a collection of cacti in the future, making your own soil and experimenting is a way to go.
Most of the time, making your own soil mix for cacti will be cheaper than buying a bag of a potting mix. This is especially true if you have multiple plants. But if you decide to buy cacti soil, make sure it is suitable for your group of cacti (desert, jungle and others).
It is a good idea to buy a cactus potting mix if you don't have many cacti, any time to make the soil or don't want to experiment (and potentially kill a few plants during this process). So if you do experment, start with the "cheaper" plants.
The biggest issue with cacti is soil that retains too much moisture. Their roots are shallow and fragile, and can easily succumb to root rot if their potting soil stays too moist.
Cacti require a specific soil composition and texture. Having said that, it is important that cactus soil is airy and quite loose, especially when wet. Cacti soil must allow good drainage and airflow. The soil mix should soak in the water and re-wet very well.
Even making sure you water lightly and occasionally won't help if the soil is holding onto every bit of moisture it can. Even high humidity can cause problems with some potting soils!
So if you've tried raising cacti before and run into issues, try swapping out your soil for something specifically cactus friendly. You might be surprised what a difference it makes!
Potting soil mixes can vary greatly depending on the manufacturer and what the soil is intended to do, but in general, soil designed specifically for cacti stands out.
There are five major reasons why:
1. Reduced Moisture Content - Most potted plants can tolerate staying a bit damp, as long as they're not constantly soggy. In fact, some plant mixes even include extra hydrophilic (water-loving) components that grab and hold onto extra water, helping plants stay perky between waterings.
But that would be a death sentence for desert dwelling cacti, which are used to occasional dousings during the rainy season, followed by weeks or months of no water at all.
Cactus soil for potted plants helps mimic this by ditching some of the hydrophilic materials in favor of non-absorbent options like perlite and grit.
However, it's important to note that while you want to reduce the moisture content in cactus soil, you don't want to eliminate it entirely.
Though the cactus can probably survive if not completely neglected, allowing the pot to entirely dry out and remain dry causes several problems.
1. It can cause the soil to compact, making it tough for the cactus to send out new roots.
Cacti have very shallow root systems already, so making it difficult for these to expand can be a real detriment to the plant's growth and health. 2. It can make it difficult to properly water your cactus later.
Soil that has completely dried and compacted tends to allow water to simply run off instead of soaking in. While cacti do have highly efficient root systems capable of taking in water quickly, these are designed for rainstorm length events in the desert, not a quick pass with a watering can on Tuesday afternoon.
This is one reason why simply planting your cacti in sand doesn't yield good results. Ideally, you want a soil that will hold just enough moisture to keep from solidifying without feeling damp.
Less Organic Matter
Naturally most desert cacti grow in soil that is low in nitrogen. Too much nitrogen in the growing medium can cause your cactus to grow very fast, causing the stem to stretch. Cacti soil must not contain any manure, as it will lead to growth of fungus that cacti's roots cannot fight. And, don't use any organic fertilizers for cacti (except for epiphytic cacti).
Though cactus soil might be mostly inorganic materials like rock and sand, it will also contain a small amount of organic material to promote plant growth, hold onto a bit of moisture, and break up the soil a bit.
Organic matter refers to anything that was once alive, like compost, peat moss, coconut coir, wood chips, and basically anything else that's not rock or sand. These materials are what plants use for nutrients, after they've been broken down by critters like insects and bacteria.
In a potted plant, there's typically very little insect action going on, so organic materials can take a long time to break down. That's why lots of potting mixes also include more accessible nutrients, like fertilizer preparations or compost, which is organic material that's already started breaking down.
Cacti, on the other hand, aren't used to rich soils, so mixes developed specifically for them tend to leave out much (but not all!) of the organic material.
As you might have guessed from the "less organic matter" section above, cactus soil is typically nutrient poor.
Not only does it lack the broken down organic matter that other soils rely on, it will typically also lacks any additional fertilizers, like the nitrogen, phosphorus, and potassium salts that typically make up dissolvable fertilizer crystals and pellets.
Other types of plants would be absolutely miserable in such poor soil, but for slow growing cacti used to sandy deserts, it's perfect.
Too many nutrients can actually cause "burning,” or damage to the plant, or unhealthy overgrowth as the plant tries to put all the food to use before it's gone.
Instead of rich potting soil, opt to feed your cacti with occasional doses of water-soluble fertilizer or compost tea.
Your cactus plants will do best when fed lightly in the spring as they start to come out of their dormant phase, and, if they're some of the faster growing varieties, perhaps again in the summer.
Don't feed in winter, when your cactus is dormant, as it won't be able to put these nutrients to use, and never overfeed!
If you're not sure whether your cactus has had fertilizer recently, err on the side of caution and let it go until spring.
Well-aerated soil is one thing that sets commercially developed cactus soils apart from cacti's natural environment. Desert soil often ends up compacted and dense, making it tough for cacti to grow and spread.
Aerated cactus soil for potted specimens, on the other hand, makes it easy, which can speed up growth, flowering, and, for varieties that multiply, you may even see more little baby cacti forming!
What makes for well-aerated soil? For cacti, a high percentage of inorganic materials, like rock and grit.
Specifically, you want lightweight, fluffy materials. Perlite and pumice are two excellent options. These are both naturally occurring types of stone that are very porous, which makes them very lightweight for stone.
They encourage airflow in soil and hold just enough water to help keep the soil around them from becoming tightly compacted.
This one might seem like another no-brainer, especially after #1 on the list here, but it's actually very specific. The drainage properties of a soil actually have more in common with aeration than moisture content, because drainage is about how well water circulates rather than how much sticks around.
With cactus soils, you want excellent drainage so that the water holding parts of your soil don't end up like a sponge, holding too much water and causing rot.
You can create well-drained soils several ways. First, the soil itself should have a relatively low percentage of soakable hydrophilic materials like peat moss or wood shavings.
It should have a high percentage of lofty, relatively non-absorbent material like perlite, rough grit, or even small stones.
All of these help keep liquid moving through the planter as you water.
You should always make sure the container you're planting has drainage holes; this is doubly important for growing cacti.
Add a layer of stones or pea gravel to the bottom of the pot. This will keep those drainage holes from becoming blocked with soil.
Importance of pH levels in cacti soil
Almost all cacti require an acidic soil to grow and thrive. Some cacti species will need higher acidity soil than others.
Generally, you need to make sure that the cacti soil mix is in the pH range of 5-6. Genus of Epithelantha, or button cacti, can do well in a more alkaline soil mix with pH levels of 6.5. Any soil mix with pH that is less than 4 and higher than 7-7.5 will cause death of cacti.
This type of soil mix is not suitable. If you have prepared a soil mix and pH levels in it are too high, you can lower pH levels by adding some peat.
But note, that there are different types of peat and some are more acidic than others, so you will need to add it gradually, then mix and check again. To determine pH levels in the soil, you can use a meter that measures moisture, pH and light levels. Here is a LINK for some PH meters.
Making Your Own Cactus Soil
There are lots of specific recipes for different plants, but in general, you want a blend of lightweight materials that does not hold much water. Such as sand, pumice stone, or perlite, paired with a small amount of peat moss or coconut coir, that will keep just enough moisture in the mix to prevent it from completely drying out and solidifying.
In a pinch, you can even take leftovers from a bag of regular potting mix and blend it with your sand and perlite for your own cactus soil.
Make sure not to use too much potting soil, and avoid using compost mixes like leaf mold or manure, as these will be much too nutrient rich.
Some ingredients often used for making cactus soil:
Peat - it is one of the main ingredients for making a cacti soil mix. Peat makes the cacti soil mix porous and lowers the pH levels. The only downside that peat can bring is difficulty with soil re-wetting.
Pumice/perlite - choose one of these ingredients to make your soil mix airy. Perlite is usually more available for sale and is easier to find. One of these ingredients is essential to let the water travel in the soil mix.
Gravel/lava rocks - gravel or other rocks will be coarse and will help to make the soil mix loose and airy.
Sand - sand will also help to make your cacti soil airy. Make sure to choose coarse sand.
Potting soil - you will need potting soil to mix with other ingredients. You can buy some ready-made standard potting soil or make it yourself.
Coir - it will help retain moisture in the mix and will provide structure. Use to replace peat moss.
Charcoal - charcoal is a soil conditioner that will help prevent diseases by absorbing impurities.
As you're blending up your soil, keep in mind that cactus soils will look much lighter in color than most potting mixes you might be used to.
Not All Cacti Grow the Same
One reason you may want to make your own cactus soil rather than picking some up at the store is because not all cacti have the same needs. Some need slightly more moisture, while others need a light and airy mix.
Some epiphytes, or "air plant” cactus varieties might prefer to sit on a bed of wood chips, if it's usually found growing on trees in nature.
A small genus of cacti with six to nine species found in the coastal mountains of south-eastern Brazil. These plants grow on trees or rocks in habitats that are generally shady with high humidity, and can be quite different in appearance from their desert-dwelling cousins.
Some tropical cactus plants might even need regular potting soil! Check the requirements of each variety you're looking to cultivate to see if any of them call for something extra particular.
Epiphytic cacti naturally grow on and around the trees by attaching themselves to tree branches for support. These types of cacti prefer soil that gives them more support and holds moisture for longer.
So, for epiphytic cacti add more peat in the soil, or even better – orchid bark that will make the soil airy but will also provide support and retain the moisture. Desert cacti will need more sand.
Cacti are a versatile family of plants. Though they can be particular when it comes to their living arrangements, once you've got them settled in the right soil, they're easy to please.
So, how to make a homemade cactus soil?
You will need to prepare cacti soil depending on the type of a cactus you have – desert vs. jungle (hot area inhabitants vs. cacti inhabiting rainforests).
The soil mix for cacti will be following:cactus soil - buying or a homemade cactus soil instructions
2 parts of a ready potting mix or made at home. To make your own potting mix add sand, perlite and peat mixed together (0.5:1:1).
Sterilizing cacti soil before using it
As noted, cacti are often very sensitive to any bacterial or microorganism growth in the growing medium. This is especially true if you use ingredients from outdoors.
If the soil mix is contaminated, it will cause death of a new cactus or even spread of the infection to other cacti. This is why it is a good idea to sterilize the soil mix before using it. One of the ways to sterilize the cacti soil mix is by heating.
sterlizing cactus soil
To do this, place the soil mix in a glass container or a pot, place it in another large pot with hot water and keep it on a slow cooking mode. This method is also called bain-marie. Keep heating the water inside the pot until it reaches a boiling temperature of 100 degrees Celsius (212 Fahrenheit).
This can take 20-30 minutes, depending on the amount of water. After it has reached boiling temperatures, turn the cooker off and leave the soil mix to cool down. A good tip is to leave the soil mix outside for few days before potting your plants.