Monstera deliciosa: why its roots rotted and what a moss pole changed

TL;DR

• The root rot did not have a single cause. I suspect a combination: hard, mineral-rich tap water (EC about 700 µS/cm, pH about 8), watering too rarely, which led to secondary rot of dried-out root hairs, and EC that was too high for roots not prepared for it. I don’t know which was the main cause, or what would have happened if the plants had grown by a huge south-facing window. Maybe then they would have coped with all of it.
• At first I was naively afraid of overwatering and waited for the moisture meter to read 1. Today I suspect that this is exactly how I dried out the root hairs.
• I’m sticking with a loose aroid mix. Neither peat soil nor semi-hydro suits the way I grow plants.
• The biggest jump in leaf size on my green monstera (from 22 to 32 cm) coincided with spring and summer, the switch to RO water, silica and more frequent watering. I don’t know which of these did it.
• The moss pole triggered massive root growth, but the leaves show nothing yet: the first leaf after the pole has the same number of fenestrations (7) as the previous one.

Introduction

Monstera deliciosa is still one of my favorite plants, and I can’t imagine my collection without one or two of them. But at my place it has never been as easy as people often claim. I have seen huge monsteras growing in plain supermarket soil and badly sized pots, usually in homes with huge windows. Mine were much less forgiving, and for a long time root rot kept coming back, even though I tried very hard to be careful.

First failures

My first serious mistake was repotting too quickly into a mix that stayed wet for too long. The plant looked healthy at first, but the roots soon turned brown and mushy. I tried to save it: I trimmed the rot, moved it into a smaller pot and switched to a chunkier aroid mix. New leaves eventually appeared, but they were small, damaged and clearly unhealthy. When I checked the roots again, the substrate at the bottom of the pot was still wet a week after watering. That was when I gave up on saving that plant and started over.

Later I lost a large form as well. It struggled from the start and never seemed truly established. I moved it into a clear pot and added about 20% peat-free soil because the roots looked a little dry. Two weeks after watering the roots were black and mushy, and even the top could not be saved, because the rot had reached the inside of the stem.

The pattern came back this year. In March I logged rot of the fine roots on my current big large form after moving it out of the nursery mix.

The first, naive lead: overwatering

At first I naively decided the problem was simply overwatering. I used a moisture meter, not accurate, but with repeatable readings. After watering it usually read about 10, and I waited until it dropped to 1. I was surprised how long that took. I expected signs of underwatering, but the plant stayed firm and started putting out healthier leaves, so I considered the problem solved.

Today I see it differently. With wet nursery soil the waiting made sense, but by making sure the substrate dried out completely deep in the pot, I probably dried out the fine root hairs, which then rotted after the next watering. More on that below.

There were several causes

For a long time I looked for a single culprit. Only later did I understand that there were probably several causes, and it’s hard for me to say now which was the main one.

Nursery soil. The mixes monsteras come in from the shop stay wet for a long time after watering. My first lost plant and this year’s fine-root rot on the large form both started in such a mix or right after it was removed. I’m not claiming the substrate itself was to blame: after all, the plant grew in it in a greenhouse, with huge amounts of light, good ventilation and optimal feeding. That substrate simply doesn’t work in my suboptimal conditions.

Watering too rarely, paradoxically. I suspect I kept the substrate dry for too long and the dried-out root hairs then rotted secondarily. What speaks for it is that the roots, both soil roots and aerial roots, grew poorly. Surprisingly, once I watered more often, root growth exploded on all my monsteras. Plants that had barely made any aerial roots started producing them en masse. I watered the green one every 6–12 days in February and March, and every 3–7 days from mid-May to the end of June. That is an observation, not an experiment: at the same time I changed the water and spring arrived.

Since adding the pole I water the green one’s substrate less often again, every 7–14 days, but that isn’t a return to the old mistake. I water the pole every few days, so the aroid mix is inevitably moist more often. I water this plant somewhat by eye, because the pole adds to the weight of the whole thing. Eventually I want to water only the pole, but first I need to make sure the roots have colonized it enough.

Hard tap water. After moving to a new flat, I noticed heavy limescale everywhere and much drier skin on my hands. The water had a general hardness above 20 dH, EC around 700 µS/cm and a pH hovering around 8. I had never checked these values before, but subjectively there was less limescale in the kettle and I didn’t have these problems with my skin. I suspect that with water like that, plus feeding at the label dose, the roots struggle to take up water and nutrients.

Light. My window faces south, but it is barely 170 × 120 cm. The plants stand to its sides, so none of them gets sun all day, and none is closer than a meter from the glass, where there are already a lot fewer lux. The green one and both Thai Constellations stand on the right, deeper in the room, under Sansi grow bulbs, 45 W in total for 12 hours a day. Both large forms stand on the left and get plenty of scorching afternoon sun, with no grow lights. In my opinion the DLI is moderate and actually sufficient, but far from nature, a greenhouse or a big patio window. I suspect that gives my monsteras a smaller margin of error: with less light they use less water, so the substrate stays wet longer. My location is part of it as well: Northern Europe is not ideal for fast monstera growth, even with extra light. I wrote more about light in The Bitter Truth of Growing Tropical Plants.

Semi-hydro and EC that was too high. I finished off one monstera after moving it into 4–8 mm LECA. Judging by the symptoms, a nutrient solution of around 1000–1100 µS/cm killed its roots, especially since they were not yet fully adapted to semi-hydro. I lost another one when moving it from LECA to Lechuza PON: classic root rot, probably from overwatering the PON. Both hypotheses rest only on symptoms, because I have no logs from those plants. For comparison, the green one in aroid mix got a solution of about 800–1100 µS/cm until July and showed nothing similar. So what probably matters is not the value alone but whether the roots are adapted to the type of substrate.

That doesn’t mean monsteras never grew for me in semi-hydro. I kept one in PON and one in LECA side by side. The one in PON grew well for a long time, until thrips I didn’t notice in time tore both of them up so badly that I gave up (more in the post about pests). I no longer have any monstera in semi-hydro, because I find that kind of substrate harder to get a feel for.

Why I’m staying with aroid mix

I know many people keep their monsteras in good shape in regular peat soil. Despite more experience, I don’t intend to try it. Even if it could work with good light and perfect nutrient chemistry, judging when the substrate has dried out “by weight” would definitely be my problem. Second, because such soil holds so much water, I think it can work for plants with a very extensive root system, adapted from the start to limited oxygen (root remodeling). That’s why I still consider a loose aroid mix the best substrate. My current one is ultra chunky, designed for regular drenching with lots of water, so unlike the “chunkier” mix from my first failure, it’s almost impossible to overwater.

I also know from experience that semi-hydro, both Lechuza PON and plain LECA, can give great results. But that style of growing feels a bit unnatural to me and causes problems in the long run: salt build-up, keeping a long enough dry phase for PON, and the right reservoir level for LECA. Still doable, but awkward when most of my plants grow in a chunky “stew” of aroid mix.

Water and nutrients

It took me a long way to get to watering that works. At first I mixed tap water with RO water, with slightly more RO. My log shows GH 10 dH in February and March. Since mid-May I have used pure RO, checking the pH and correcting it when needed.

Around the same time I was feeding with Hesi Hydro Growth alone, and faster-growing plants with thin leaves, such as Homalomena rubescens ‘Maggie’, started showing symptoms typical of calcium deficiency. The monsteras didn’t show them, but that may have been a matter of time. RO water brings no calcium or magnesium, and one-part fertilizers usually contain little of them, because in a concentrated solution calcium precipitates with sulfates and phosphates. So first I started adding Biobizz CalMag (1 ml/l) to the RO water, and for the last 2–3 weeks I have used the two-part Plagron Hydro A+B, which seems to solve the problem. I don’t add anything else to it.

From February to July the monsteras got a solution of about 800–1100 µS/cm, and 500–800 µS/cm since August, at pH 5.5–6. From April to August I also added silica (SiO₂) every now and then. I decided that a lower EC gives me a bigger safety margin, because salts build up over time (runoff EC higher than the EC of the solution).

The green deliciosa on a moss pole

I tried growing an ordinary green monstera (often called ‘Borsigiana’) on a moist sphagnum moss pole. About 8 weeks ago, in early September, I moved it from a 13 cm pot into a clear 17 cm one with a chunky soilless aroid mix and added the pole. So I changed three things at once and can’t separate their effects.

Since February 2026 I have kept a diary of measurements. The green one has produced five leaves since:

Leaf	Appeared	Length × width	Fenestrations
1 (at purchase)	–	22 × 19 cm	5
2	18 Mar	22 × 19.5 cm	5
3	around 2 Jun	29 × 25.5 cm	5
4	around 31 Jul	32 × 26 cm	7
5 (after the pole)	22 Oct	25 × 21 cm, still growing	7

The biggest jump in leaf size, from 22 to 32 cm, fell between March and August, when I switched to pure RO, added silica and watered more often. But that is also spring and summer, and in the same period both Thai Constellations started making bigger leaves too (table below). On top of that, leaf 3 appeared just 2 weeks after the switch to RO, so most of its growth happened before it. Once again I don’t know which factor mattered most.

Roots

The effect of the pole on the roots is obvious. It caused massive root growth in every possible direction: even up the pole and eventually outward.

The soil roots also became very active, and some came out through the drainage holes.

I can’t say how much of that is the pole and how much the new substrate and the earlier change in watering rhythm.

Leaves

The leaves show nothing spectacular so far. I waited about 8 weeks for the next leaf after the last measurement of the previous one, but across the whole log new leaves appeared every 11, 8.5 and 12 weeks or so, so this is no unusual pause. The first leaf after adding the pole looks pretty, but it probably won’t be as big as I expected: its number of fenestrations is exactly the same as on the previous one, 7, and its current size (25 × 21 cm on 1 November) doesn’t suggest it will be bigger. It is still growing, so maybe the effects need more time.

The pole doesn’t work here as obviously as with Epipremnum aureum, where every new leaf is bigger and the growth rate makes the effects easy to see and spectacular. Still, I’ll keep this plant on the pole, because it tends to stretch its internodes, and the pole will let me reset it safely with minimal risk of reversion. I describe a similar pole on Monstera adansonii.

Large form or small form?

The debate about large-form versus small-form Monstera deliciosa keeps coming back online. Some growers say the difference boils down to maturity and conditions, and I think that is partly true. Poor light definitely stretches internodes and petioles. You can find old monsteras with small leaves, as well as plants in brighter rooms putting out impressive ones.

Still, I don’t believe conditions explain everything. My young Thai Constellations had large leaves from the start and each new one was bigger, even though my light is far from ideal. The geniculum of a young Thai already shows the characteristic ruffles, while a green one of similar size has none.

I also have two large forms. Both are rooted tops, so they didn’t start from scratch. The big one makes the largest leaves I have, while the smaller one, the second plant from the same pot, makes leaves roughly half the size, yet despite that it already has the ruffles and extremely short internodes.

For comparison I pulled the logs of five monsteras. Lengths are per leaf, in the order the leaves appeared:

Plant	Length of successive leaves (cm)	Fenestrations	Internal holes	Gap between leaves (weeks)
green	22 → 22 → 29 → 32 → 25*	5 → 5 → 5 → 7 → 7	0 (leaves 1 and 3)	11 → 8.5 → 12
Thai 1	27.5 → 29 → 33 → 34.5	6 → 7 → 9 → 11	3 → 2 (leaves 3 and 4)	9 → 6.5 → 10
Thai 2	32 → 32.5 → 32 → 37 → 38	7 → ? → 10 → 11 → 11	0 → 1 → 1 (leaves 3–5)	6 → 8.5 → 8.5
large form, smaller	26 → 23 → 27*	8 → 4 → 6	0 → 0	18
large form, big	53 → 49 → 52	17 → 18 → 17	15 → 10 → 17	13

* leaf still growing. I have kept the diary since February–March 2026, so this is a short series.

The Thai have bigger leaves, more fenestrations and their first internal holes, while the green one, after all the changes, only reached the size the Thai had in March. The big large form has leaves 40–50% longer than the Thai. That matches my hunch, but the comparison isn’t clean: the large forms stand on the left, sunnier side of the window.

If one of my young green specimens ever starts producing massive leaves with plenty of internal fenestrations, a ruffled geniculum and a thick, rough petiole, that will be the ultimate proof for me. Until then these are just hypotheses.

Lessons learned

I approach plant problems the way I approach bugs in software: I want to know what failed and why.

• My root rot had several intertwined causes, not one: nursery soil in my conditions, water quality, watering frequency, nutrient EC, and light that doesn’t leave much margin for error.
• Watering too rarely can be as harmful as watering too often. I suspect dried-out root hairs then rot secondarily.
• What matters is not only how often I water, but also with what.
• Once rot reaches the stem, saving the plant is hard and sometimes impossible. Then it’s better to cut back hard and root the healthy part in water. It worked for me once, but it’s a rescue plan, not the goal.
• I’m not swapping aroid mix for peat or semi-hydro.
• A moss pole does to the roots what I expected. Whether it will do anything to the leaves of the green monstera, I don’t know, but I’ll update the post as soon as I measure the next ones.