If you're determined to make your succulents and cacti grow at full speed, the starting point is the substrate. It's where water, air, and nutrients coexist, allowing the roots to function like clockwork. A good growing medium is like a well-ventilated house: It drains quickly, retains just the right amount of moisture, and allows oxygen to pass through..
The goal of this guide is for you to master the formula of perlite, peat and humusAdjust it to your climate and your species, and also control the pH so that nothing hinders growth.
It's worth remembering something that every seasoned fan repeats: There is no single one “perfect” substrateBecause each plant, its watering needs, and its environment are unique. Some succulents prefer slightly acidic environments, while others thrive in calcareous soils; even within the same genus, there are nuances. For example, some growers cultivate Haworthias with excellent results in pure pumice stone. The important thing is to understand the pieces of the puzzle (components, pH, structure) and combine them thoughtfully.
What should a succulent substrate provide?
A well-designed medium should facilitate several things at once: rapid drainage of excess waterAeration between particles, and a moderate moisture reserve to prevent the roots from dehydrating between waterings. No perpetual puddles or suffocating mud.
- Drainage without stagnation: The mixture must drain excess water quickly to prevent mold and rot. Coarse mineral components (washed sand, pumice, volcanic gravel) are your allies.
- Air for the roots: Internal porosity is key. Perlite and pumice create voids that improve oxygenation and prevent compaction.
- Precise hydration: Materials such as coconut fiber, peat, or a touch of humus support a moderate humidity between waterings without turning the pot into a sponge.
- Organic-mineral balance: The usual composition is a mineral base (perlite, pumice, sand) with a small organic percentage (peat, coconut, humus) for nutrition and structure.
- Climate adjustment: In humid environments it is important to increase the mineral fraction; in dry climates it is advisable to add more coconut fiber or peat so that everything does not become "dry as a bone".
In practice, many people use sphagnum peat (a medium-to-black mix) and coarse sieved sand of 0,6 to 3 mm to improve aeration, sometimes with a pinch of ground charcoal due to its filtering effect. Pay attention to the particle size: excessively fine particles clog pores and worsen root respiration. If you want to learn more about types and characteristics, consult [link/reference]. substrate types.
Key components and what each one is used for
Minerals that provide structure and air
- Perlite: Ultra-lightweight and highly porous; prevents clumping and improves air circulationIt also retains some water in its pores.
- Pumice stone (pumice) and volcanic gravel: They stabilize the mixture, provide sustained drainage, and help the pot do not compact over time.
- Washed coarse sand (silica or river sand): Its function is to "open up" the texture. The ideal grain size for potting is between 0,5 and 2–3 mm. avoid the blockage fine porous.
- Expanded clay/arlita: larger pellets that are usually used as a bottom layer or in hydroponics for improve evacuation of the water.
Organics that regulate moisture and nutrients
- Blonde and black peat: high retention capacity; blonde is more porous and acidic, black less acidic and very capable of retaining waterThey tend to compact if overused.
- Coconut fiber: It retains moisture, maintaining porosity better than peat. It is poor in nutrients, so does not replace the subscriber.
- Worm humus (in low doses): It improves structure, provides microbial life, and gentle nutrients. It is suitable for use as corrector and not as a base.
- Pine bark and sphagnum moss: They are used as padding, to retain moisture, protect against heat/cold and promote aeration in specific crops; sphagnum is also great for cuttings and supports with aerial roots.
- Charcoal: It can be mixed in or placed at the bottom; it acts as a filter. limits fungi and improves drainage.
If we had to choose just three versatile "wild cards" for succulents, many growers would choose perlite, coconut fiber and bark (depending on the use). From that trio you can refine with sand and pumice according to your climate and type of pot.
pH: the key for roots to take advantage of nutrients
pH governs the availability of elements. The scale is logarithmic: Lowering pH from 6 to 5 is multiplied by 10 the concentration of H+. This explains why small adjustments change the behavior of the substrate and the irrigation water so much.
To ensure that macroelements (N, K, Ca, Mg, P, S) and microelements (Fe, Mn, Zn, B, Cu, Mo) are truly available, it usually works wonders to keep the substrate between pH 5,2 and 5,8At pH 5,2–5,4, overall absorption is very balanced. In soil cultivation, due to soil structure and the presence of bicarbonates, it is recommended to be around pH 6 to avoid “collapsed” soils.
Keep in mind that many organic fertilizers tend to acidify the mediumUsing very acidic substrates (for example, pH 5–6 kanuma intended for azaleas and maples) may not be the best idea for most succulents if you don't carefully control watering and fertilization.
When calcium is lacking or the substrate becomes excessively acidic, agricultural gypsum (calcium sulfate) is a great ally: buffers pH and provides Ca as long as there are active granules. However, it's not limestone; it corrects the pH without raising it as much as traditional liming.
pH in water, fertilizer tanks and substrate
- Irrigation water: It is recommended not to go below pH 4,8 to avoid direct damage to rootsValues above 4 are not usually problematic in the short term, but sustained over time they can limit microelements.
- A/B Deposits: In nutrient solutions, tank A usually performs well between pH 4–6. In tank B, it's best not to exceed [a certain range]. pH 5 to avoid precipitation and clouds in the solution.
- Substratum: A range of pH 5,2–5,8; in living soil, around 6 for structural reasons.
How to measure and correct pH without messing it up
- Measure in soil/substrate: Mix 1 part of sample with 2 parts of distilled water and measure with a pH meter reliable.
- Measure in water: Use a calibrated pH meter; if the water contains a lot of bicarbonate, consider acidifying it to ~0,5 mmol/L of HCO₃⁻A small amount of bicarbonate buffer is positive because it stabilizes the pH.
- Correct: To lower pH you can use nitric acid (note, add N) or phosphoric acid (only in tank B). Doses should be moderate for do not break chelates nor burn roots. To raise soil pH, limestone is used; to lower it, ammoniacal fertilizers help. With substrates, the safest thing is to adjust the water pH and choose acidifying or non-acidifying fertilizers as appropriate.
Important warning: Lowering the pH of the water too much to "force" the drop in the pot can lead to other problems: blockages, burns in radicles and changes in substrate structure. It's best to proceed with caution and take measurements.
Recipes that work: perlite, peat and humus well combined
A very effective universal potting mix for succulents combines minerals that open up the soil with a light organic mix that provides just the right amount of moisture. A balanced recipe to start with is: 2 parts coarse sand, 1 part perlite, and 1 part peat or coconut.Drain quickly, aerate, and hold a sip of water.
Another commonly used formulation for ornamental pots, which is easy to find and mix, is: 50% black soil/compost, 30% peat, 15% perlite and 5% sandFor cacti or Lithops, you can lower the peat and increase the mineral fraction for faster drying.
How do you know if you've found the right consistency? Moisten a handful and squeeze it tightly; if when you open your hand the lump crumbles easily and the texture is light and looseYou're on the right track. If you notice it's hard, compacted, or, on the contrary, too porous, adjust it: more coconut/peat if it dries out too much, more sand/perlite/pumice if it retains moisture.
For pots without drainage holes (not ideal, but we've all been there), add a layer of gravel or expanded clay at the bottom And use an even more porous mix than usual. If you're recycling garden materials, sterilize them at a low temperature in an oven or let them dry in the sun to minimize pathogens.
Adjustments based on weather and location
- Damp or cold environments: The pumice, sand, and perlite rise; the organic matter falls. The goal is for the water Don't stand still.
- Dry and warm climates: Slightly increase the coconut fiber or add a pinch of vermiculite to prolong the humidity without flooding.
- Outdoors with wind and sun: They dry quickly; they tolerate a bit more organic matter. Indoors, the most important thing is... aeration to avoid excess humidity.
Maintenance that makes the difference
The substrate also ages: it decomposes, compacts, and accumulates salts. Renew it every 18–24 months It keeps the potting mix aerated and healthy. There's no need to wait until the pot is bursting: at the first sign of uneven drying or slow drainage, values the transplant.
Between changes, occasionally remove the top layer with your fingers to break scabsImprove water and air circulation. If you notice the mix is very "tired," a small addition of worm castings will reactivate microbial life without over-fertilizing.
A classic trick: add ground charcoal It reduces the risk of fungal growth, especially on cacti. You can also add some charcoal mixed with the gravel at the bottom to improve filtration.
And speaking of fertilizer: many growers prepare the fertilizer in the irrigation water with soluble powdersIt's convenient and precise. Remember to adjust the pH of the solution and alternate periods of fertilization with clean water to prevent buildup.
Hydroponics and succulents: mixing vs. combining, and the tiered approach
In soilless cultivation or in highly mineral substrates, it is useful to distinguish between two approaches: Mix (to achieve a homogeneous composition) and combine (Arrange in layers or levels with different functions). This second option is very useful for fine-tuning drainage, solution reserve, and anchoring.
Lower level (up to ~7 cm)
It functions as a drainage base and oxygen reservoir. Large grains are the dominant grains here. gravel, river sand, red/black tezontle, expanded clay or ceramic fragmentsIn addition to charcoal or mineral charcoal. The more air you keep at the bottom, the safer the roots will be.
Middle level (the “root zone”)
This is where roots and rootlets develop. For small plants or those with underground growth (radishes, carrots in gardens, lettuce, herbs), prioritize substrates light and small grain (≤5 mm): perlite, vermiculite, rock wool, ground pumice, and, if you're looking for economy, mixes with a heavy fraction of 40% maximum. A guideline ratio: 60% light + 40% heavy.
For medium and tall plants (peppers, cucumbers, melon, tomato), better anchoring is needed: you can work almost exclusively with heavy fraction (tezontle, river sand, gravel, tepojal), with medium grain of ~2 cm, or combine 80% heavy + 20% lightIn this case, germinate in a seedbed and then transplant to the final substrate.
Top level (final layer)
It's not always mandatory, but it adds an extra touch of stability and reduces evaporationPlace a thin layer of river sand, gravel or tezontle of ~2 cm when the plant is established (at low heights, you can do without it until it produces 4 true leaves).
Examples of functional proportions
- Tall stature: 50% tezontle + 50% mixture of vermiculite and perlite (25% and 25%).
- Medium/small size: 40% tezontle + 60% perlite/vermiculite.
- Underground: 20% tezontle + 80% perlite/vermiculite for maximum softness medium.
Ready-made commercial mixes
If you prefer to save time, there are standardized combinations that cover different needs. For example: 20% perlite + 20% vermiculite + 20% humus + 40% peat moss for warm climates or infrequent irrigation; 40% perlite + 60% peat moss to germinate and strengthen roots; 30% perlite + 10% vermiculite + 10% humus + 50% coconut fiber for versatile vegetables; 40% perlite + 60% coconut when you want an inert medium and total control of the nutrient; or even 50% perlite + 50% humus for small/medium plants where you do not add additional nutrient solution.
Sustainability and choice of materials
Peat works, but its extraction has environmental impact Because it comes from peat bogs with high ecological value. Coconut fiber, on the other hand, is a byproduct with good porosity and drainage. If possible, prioritize coconut and reduce peat, especially in mixes where you want to avoid compaction in the medium term.
Worm humus is not an "all-in-one": improves structure and nourishesBut it won't eliminate the need to fertilize when necessary. Use it sparingly to avoid overloading slow-growing plants with nutrients.
Pine bark and sphagnum moss are great resources such as padded To protect from heat or frost and to maintain extra surface moisture without waterlogging. They are essential for orchids, but can be used occasionally for succulents, for example, for cuttings or as a decorative finish that also regulates evaporation.
Special cases, fine-tuning, and emergency solutions
Some succulents are more tolerant of humidity (Haworthias, Gasterias) and others require it. express drying (cacti, Lithops). For the former, a little more organic fiber can be beneficial; for the latter, increase the mineral content and use coarser soil. If you water with hard water (high in bicarbonates), consider a slight increase in the amount of organic fiber. acid adjustment to maintain pH within range.
In cases of calcium deficiency symptoms (apical necrosis, "watery" tips), agricultural gypsum provides a solution without raising the pH too much: provides Ca and stabilizesIf the problem is a clearly high pH, you can introduce ammoniacal fertilizers in moderation to lower it. Conversely, if the pH is too low, a light liming will raise the value and improve the soil structure.
One more practical tip: lower the pH of the water with nitric acid It adds extra nitrogen, which can be positive during the growth phase but less desirable during dormancy. phosphoric acid It doesn't add nitrogen, but remember that it's handled in tank B to avoid solubility problems. Adjust the dosage gradually and always measure.
Finally, don't forget that every watering method is different. The same substrate will behave differently depending on the watering technique. Observe, ask questions, compare results, and... adapt it to your routineThat's the safest way to nail the mix to your environment.
When you choose the right mineral fraction (perlite, sand, pumice) and carefully dose the organic components (peat, coconut coir, humus), monitor the pH within the range of 5,2–5,8, and keep the substrate alive and aerated, succulents respond with more roots, less fungus, and much more stable growthAdjust proportions to your climate and species, use pH as a compass and rely on ready-made levels or mixes when appropriate; with that combination, doubling vigor is no longer a matter of chance.