Choosing the Right Mix for Tropical Plants

When I started growing plants, one of the most important things I learnt was how much the mix matters. The leaves are what we notice first, but it is the roots that live with every choice we make about what goes into the pot. A mix can help a plant grow or quietly work against it. I learnt that by making plenty of mistakes.

My growing journey did not begin in a greenhouse. It began with cuttings in a jam jar of water on the kitchen bench. Since then, I have grown plants on bedroom windowsills, in bathrooms and living rooms, outside and, eventually, in a greenhouse. I have cared for them through humid summers and dry indoor winters. Every move changed something about the light, warmth, airflow or humidity. But I kept coming back to the same question: what is happening around the roots?

I have lost plants while thinking I was doing the right thing. I watered carefully, waited for a pot to dry, or perhaps let it dry too far. Sometimes the problem was not simply when I watered. The mix held water for too long, dried unevenly or left too little air around the roots. I have bought nursery mixes expecting them to suit the plant named on the bag, then found I needed to change their texture for my plants and conditions. It is a painful lesson when you have saved up for that plant.

That does not mean every bagged mix is poor. An Australian Standards-marked mix is a useful quality starting point, and some plants do well in it as sold. A label such as “premium” or “aroid” still cannot account for your pot size, your room in winter or the particular roots in your hands. When someone new visits my greenhouse, I tell them to look at the finished mix and be prepared to adjust it if it is too dense or holds too much water for their plant. I also make my own everyday potting mix from a bagged base, adding ingredients chosen for my plants. I do not use ordinary nursery mix straight from the bag for my collection.

One warning sign for me has been fungus gnats around a persistently damp pot. Their larvae favour moist organic media, though the gnats can arrive with a new plant or a bag of mix. Seeing them prompts me to inspect the pot; it does not mean every organic ingredient is a problem. Gardening Australia’s fungus-gnat guide explains why persistent moisture matters. Mealybugs and other pests can arrive by different routes, so I would not blame the mix for those.

This is the guide I wish I had when I started. I will take you through the mixes I prepare and use for plants I grow and sell: first for a fresh cutting, then for an established plant and, finally, for a climbing pole. I want to show why I use each ingredient and what I watch for, so you can make a better choice for the plant in front of you—whether it is a prized collector plant or the everyday one by your sofa.

In this article

What the mix is doing below the surface

Imagine slicing a pot down the middle. You would see pieces of bark, coir and mineral material, with roots winding between them. You would also see something less obvious: tiny spaces. Those spaces are the whole story. Some are large enough for water to drain away and fresh air to move back in. Smaller ones hold water close to the roots. The roots need both. They use oxygen to release the energy that helps them grow and take up water and nutrients.

Picture a watering can passing over that cut-open pot. Water enters the spaces and pushes some air out. After the excess drains, a good portion of the larger spaces opens again. If too many spaces are filled with fine, compacted material, the pot can stay wet and poorly aerated. If there are only large gaps and little that holds water, the roots may dry before the next watering. That balance is the reason I use both chunky and finer ingredients. Gardening Australia also stresses that roots need air as well as water.

There is another layer to the picture. Some ingredients, including bark and porous pumice, hold water inside their pieces as well as in the gaps around them. Nutrients dissolved in that water must reach living roots; some nutrients can also cling temporarily to ingredient surfaces. Water pouring from the bottom of a pot does not tell me whether the middle is evenly moist or whether the roots still have oxygen. A shallow pot and a tall pot can behave differently with the same mix, and pressing the mix down closes some of the larger air spaces. Texas A&M’s greenhouse guide explains the pore-size and container effects in more detail.

This is what I want a grower to remember: the pot is not a bucket of “soil” that simply goes from wet to dry. It is a changing neighbourhood for the roots. Watering, ingredient size, pot shape and compaction alter that neighbourhood every day. Fertiliser matters, but even a well-fed root cannot do its job if it spends too long without enough air.

Propagation: choosing the right start

A fresh cutting is in a delicate position. Its leaves can lose water, but it may have few roots—or none—to replace it. I want a viable node in contact with moisture without burying it in an airless, soggy mass. Light, warmth, the condition of the cutting and the humidity around its leaves still matter. A mix does not make a poor cutting healthy by itself.

Starting in water

I understand why people start a cutting in water. I did. A jar on the kitchen bench lets you see the first white roots appear, which is half the fun. Gardening Australia’s water-propagation guide shows it as a valid method for many indoor plants, including Syngonium. Keep the water clean, with the node submerged and the leaves above it; not every species or cutting will respond the same way.

The change from jar to pot is where I like to slow down. Roots formed in water can struggle when moved into a propagation mix, especially if they have grown long and tangled or the new pot is allowed to dry too quickly. The new environment asks the roots to adjust. I handle them gently and keep the fresh mix steadily moist while the plant settles in. Illinois Extension describes that transition; the Australian guide also advises keeping the newly potted mix moist.

I prefer to see more than one new root before moving a water-grown cutting. When the first roots start to branch, and those branches sometimes branch again, I feel more confident that the cutting has a developing root system rather than one fragile thread. That is my sign to watch for, not a rule every cutting has to follow. I may transfer it to a small pot of moist propagation mix before moving it into a chunkier, longer-term potting mix. I settle the medium gently around the roots and keep an eye on it during the transition.

Starting a cutting directly in a propagation mix​ avoids that water-to-medium change. Some growers use rooting hormone; it can help certain cuttings, but it is not essential for every easy-rooting aroid. A clear plastic pot with drainage holes is a simple beginner’s tool: you can watch roots reach the sides without pulling the cutting out to check. A black nursery pot works too once you know the signs, but there is no prize for making the roots harder to see.

I prepare two propagation mixes at roughly three parts prepared coir or moss to one part perlite by volume: one with coco coir and perlite, the other with long-fibre sphagnum and perlite. That is a working ratio, not a laboratory specification. I supply both moist. I judge that moisture by how the prepared material feels and holds together, rather than by a measured percentage.

Coco coir and perlite: fine and even

Coir is processed coconut husk. Its finer texture makes even contact around a node or a small new root. It holds water through the spaces within and between its fibres and particles. The lightweight white perlite interrupts that finer texture and helps preserve larger spaces for air. The two are doing different jobs; adding perlite does not turn coir into a dry medium.

One reason I like coir for some finer-rooted cuttings becomes clear later, when it is time to move them. In my experience, loose coir falls away more readily than sphagnum, which can cling to new roots. I do not have to tease long moss strands out of a delicate root system. That is a practical preference, not a rule that every fine-rooted plant must be propagated in coir.

I can get quick rooting in this mix when the conditions are right, but it asks for attention. I keep it evenly moist, not saturated. In an oversized or tightly packed pot, the coir can stay wetter than a small cutting needs. Let it go very dry and young roots may suffer as well. This is why I favour a small pot with drainage holes and check the medium rather than watering by the calendar. Gardening Australia’s perlite guide explains why perlite can help keep a mix open as the organic part ages.

Coir is not one completely uniform ingredient. Fine coir, longer fibre and coarse coco chips behave differently. A study of coir added to pine-bark substrates found that adding fine, fibrous coir changed both water retention and the spaces between bark particles. That helps explain the mechanism, but it was not a trial of my propagation mix and does not tell us which cutting will root fastest in it.

Sphagnum and perlite: loose and adaptable

Long-fibre sphagnum feels and handles differently. I can lay a node against damp strands or tuck them loosely around an awkward stem instead of filling the space with a finer medium. The fibres can hold a great deal of water while still leaving air between them if they remain loose. Perlite helps keep the moss from becoming one compressed mass. This is one reason I often reach for moss when a thicker-rooted Monstera or Epipremnum cutting needs a place to start. Those plants can also root in coir; I choose based on how the medium handles the cutting, not on a strict genus chart.

I find the loose moss mix easier to keep damp without feeling as though the node is sitting in a fine, wet paste. That is how it behaves in my hands; I have not measured whether it holds more air than my coir mix. Moss can still become compacted, and a propagation box can still be too wet.

My Monstera obliqua ‘Peru’ cuttings show why I sometimes wait before disturbing a propagation box. Several have put out new growth while roots develop through the sphagnum beneath them. I can see healthy roots at the base of the box, but I want the cuttings to establish properly before I separate them. A new leaf is exciting; it is not my cue to pull everything apart the next morning.

There is a catch with moss. It can cling tightly to new roots. When I move a rooted cutting, I leave any strands that are firmly attached in place rather than pulling them off and risking a broken root. Iowa State’s propagation guidance also notes that coarse sphagnum can be difficult to re-wet after it has dried completely. A humid-looking box is no substitute for checking whether the fibres touching the node are actually damp.

Neither mix is reserved for a particular genus. The choice is about the roots I expect, the cutting’s shape, how easily I can see and handle it, and how the container holds moisture. Once roots are established and the plant is making healthy new growth, I can think about a longer-term potting mix rather than moving it according to a fixed number of weeks.

Aroid Mix: Why Every Ingredient Earns Its Place

Once a plant is established, I need a mix that can support a larger root system through many watering cycles. My Aroid Mix​ is built from pumice, coco chips, perlite, orchid bark, horticultural charcoal and a moisture-retaining organic part. Each brings something different to the pot.

Why I use pumice

Why put pumice into an aroid mix? If all I needed was a gap between pieces, why not add ordinary stones? Part of the answer lies inside the pumice. This volcanic material is full of small pores that can hold some water, while the spaces between suitably sized pieces help water drain and air return. In a study comparing porous volcanic materials with non-porous silica sand of the same particle size, internal porosity made a significant difference to water retention.

Pumice is not magic, and every bag behaves differently depending on particle size and how many fine particles it contains. Other porous mineral materials can do some of the same work. A smooth, dense stone may add weight and create gaps, but it lacks pumice’s internal water-holding pores. A layer of stones at the bottom of a pot is different from mixing particles throughout the root zone; it will not fix poor drainage in the mix above.

I choose pumice for that combination: a durable coarse particle with some water held inside it. Coir and bark play different roles and change as they age. The pumice still has to be the right size and work with the rest of the mix.

Why I use orchid bark

“Orchid bark” describes a grade of bark commonly used for orchids; it can be useful for other plants too. Its chunky pieces give roots surfaces to grow around and create larger spaces between the pieces. Bark is not waterproof, though. Its structure can hold water, and some nutrients can cling to its surfaces rather than washing straight through. University of Georgia Extension describes these internal pores and nutrient-holding sites in pine bark. Its measurements come from blueberry production, so I use them to explain the physical idea, not to prescribe a watering or feeding rate for aroids.

Bark also changes with time. Finer or more decomposed bark generally holds more water and can leave less air between pieces than a coarser orchid grade. If a once-chunky pot becomes fine and slow to dry, that may reflect the ageing medium as well as the plant’s needs. Iowa State Extension’s component guide makes the particle-size distinction explicit.

Coco chips, perlite and charcoal

Coco chips are coarser pieces of coconut husk, different from the finer coir used in my propagation mix. They take up some water, but their larger shape also leaves spaces between pieces. Roots can grow against and around them. To me, that is more useful than simply making a pot “drain fast”: I want a root to find moisture at a surface while still having air nearby. Perlite adds lightweight mineral particles that help keep spaces open. Australian aroid growers featured by Gardening Australia also build chunky mixes around that balance, although their ingredients and proportions differ from mine.

I also add horticultural charcoal. Its pieces contribute to the mix’s structure, and charcoal can hold some substances on its surface. I have found it a useful addition and suspect it may help with some fungal problems, but I cannot say it prevents them. I have not compared otherwise identical plants with and without it. Charred materials vary enormously, and studies of specific biochars have found different effects on disease at different rates. One controlled study even found a worse outcome at a particular rate. That study did not test my horticultural charcoal; it reminds me to be careful with the claim. Good watering and an open root zone still do the everyday work.

Together, these ingredients aim to hold some moisture around the roots without leaving the whole pot packed and wet. Whether that works depends on the plant, the pot and how I water it. I pay attention to how the whole pot behaves after a thorough watering, not just to the ingredient list.

Anthurium Mix: smaller pieces, the same balance

Anthuriums are aroids, so the two mix names do not mark a botanical dividing line. Anthuriums also grow in different ways: some attach to trees, some climb, and others grow in the ground. In a pot, I want to match an open, moisture-holding root zone to the plant and its conditions. The Royal Horticultural Society’s Anthurium guide describes a mix that stays moist but open and drains well.

My current Anthurium Mix​ shares many ingredients with the Aroid Mix: bark, coco chips, perlite and horticultural charcoal, with some finer coco coir. I use pine bark as well as orchid bark in this blend, and prepare its ingredients in smaller pieces. I do not put pumice in this recipe. That sizing matters when I am working with an Anthurium whose roots are finer than the large, chunky roots I might see on a Monstera: smaller pieces make contact around those roots without my having to force a coarse chunk into every gap. I still need enough open space for air. It is a balance, not a rule that all Anthuriums have the same roots or prefer the same particle size.

I cannot say that my Anthurium Mix is always wetter or drier than my Aroid Mix; I have not measured the finished recipes side by side. A broad-leaved Anthurium in a warm greenhouse, a strap-leaved one in a cooler room and a newly rooted division can all use water at different rates. The useful question is whether the roots have both moisture and air in that pot, and whether the mix is still behaving well several months after repotting.

Moss Pole Mix​: a second root zone

A climbing plant can make roots from its stem as well as from the base of the plant. A fillable pole gives those aerial roots something to enter while the stem climbs; the pole becomes a second root zone above the pot. It does not replace the mix below. Australian growers Jazmin and Jacob, featured by Gardening Australia use a different kind of filled pole for a similar reason: to give climbing roots a moist medium they can reach.

I did not arrive at my present mix in one go. Years ago I filled poles with straight sphagnum and wrapped them with Glad Wrap to try to keep the moisture in. In the house, particularly in winter, I found I could not keep up with how quickly the pole dried. One Philodendron verrucosum also suffered a spider-mite infestation during a spell when I was struggling with the drier conditions. That experience pushed me to rethink the setup. I cannot pin the mites on the pole alone; spider mites favour warm, dry conditions, and the whole environment around the leaves matters.

I now use plastic-backed poles when I want a climber to grow upwards. The backing slows moisture loss from one side, but the filling still matters. Straight sphagnum is lovely when it is damp and loose. After repeated watering, I have watched it settle and pack more tightly. If it then dries hard, getting water evenly back into it can be difficult. An aerial root growing in that pole may lose reliable contact with moisture just when it needs it.

I tried sphagnum with orchid bark and then with very fine coco chips. Neither gave me the feel or moisture pattern I wanted in my poles. The blend I now make uses roughly equal amounts of long-fibre sphagnum and larger coco chips. Moss fibres keep contact around aerial roots. The larger chips take up some water and hold open spaces through the moss, so the filling does not settle into one dense wad as readily in my setup. The moist chip surfaces may give roots another place to find water if nearby moss has begun to dry. That is the practical “extra margin” I am aiming for, rather than a guarantee that a dry pole cannot harm a plant.

I still check and water the pole. Chips cannot make up for leaving it dry indefinitely, and I do not want the pot below sitting waterlogged just to keep the pole damp. The filling needs a support that can hold loose chips and moss. If your room, pole shape or watering routine differs from mine, watch what stays damp inside the pole and adjust from there.

Starting with a bagged mix

You do not have to buy ten ingredients on day one. I began with what I could get, made mistakes, and learnt to look inside the bag. If I am using a general potting mix as a base, I first ask what the finished pot needs: is the material mostly fine and likely to stay wet around these roots, or is it so coarse that it will be hard to keep evenly moist? Is the plant going into a small pot or a big one? Where will it live? Those questions tell me more than the picture on the packet.

For a plant that needs a more open root zone, I may work suitable coarse particles through a fine base rather than leave the base as it came. Perlite, bark and coco chips do different things, as we have seen, so I choose additions for a reason. I do not put a layer of stones at the bottom and assume the problem is solved. Nor do I follow one universal ratio for every plant. Gardening Australia’s guide to picking a mix makes the same practical point about matching and modifying a base for the job.

After potting, I watch how water moves through, what remains moist after it drains, and how quickly that pot loses water in its actual spot. A clear pot can help a beginner see new roots. Later, the pot’s weight, the drying pattern and the plant’s growth offer clues too. A yellow leaf or stalled bud does not diagnose the mix by itself—light, temperature, pests and root health can all be involved—but it is a reason to look more closely.

Growing plants in jars, rooms and now a greenhouse has taught me to pay attention to what is happening beneath the leaves. A recipe sets up the conditions around the roots, but I still have to watch the plant and adjust my care. I make several mixes because a fresh cutting, an established Anthurium, a larger aroid and a climbing stem need different things from the material around their roots. Buying a prepared amount can spare someone sourcing several full bags. More than that, I want you to understand why each ingredient goes into a pot, so you can make better choices for your own plants.