I have a Dracaena Marginata that I bought 2 1/2 years ago, that grew tremendously after I got it, but now hasn’t grown for a long time, at least a year. That is not a problem, just background information. It looks completely healthy, apart from some brown tips on the leaves, and has a big strong looking foliage. When the plant started shedding leaves after I got it (it only sheds very few now and then), I got the “clever” idea that I’d just put them on top of the pot, then they would become soil later, right? I have done so for the 2 1/2 years I’ve had it. But a few days ago I discovered something mildly troubling. The leaves covering the soil hinders some moisture from getting away, and there are actual mushrooms growing underneath them! In addition, there are white cotton-like patches of mold on the surface. I got worried about whether there might be some root rot, and lifted the plant out of the container to see how it was doing. I saw that the entire outer edge of the soil was covered with white mold patches, and that all the roots were clustered tightly together in the bottom, and growing in circles. My first hunch was that I needed a bigger pot, because the roots were tightly clustered, and to prune the roots so that new roots could grow more freely. Also, I figured I’d need to wash away as much as possible of the not-so-healthy looking soil. The current pot is 20 cm diameter, so I bought one that is 24 cm. The height of the plant, from the top of the soil, is 120 cm.
But before I was about to start repotting, I came across your posts about the dangers of potting up, and the problems of removing existing soil around roots. Also, it worried me that the soil is still moist, more than one week after last time i watered it. I water it once every week, with about 1/2 litre of water, but now it has gone 10 days, and the soil is still moist! Is it possible that potting up to 24 cm might be too much, and cause root rot, then? Or maybe I’m already having root rot?
As I told you, the plant looks completely healthy above the soil. But what I saw when I lifted the plant made me think that there are problems that might be more visible later if I don’t do something.
I am so glad your contacted me BEFORE you went ahead with your plan to replace the soil and use a larger pot. Both would be terribly costly mistakes and yet that is what most people do and then later ask me why their plant is deteriorating.
Outside in nature, dead plant tissue is exposed to changes in temperature, wind, insects and a variety of fungi and bacteria, all of which are essential for decomposition. However, those conditions do not exist indoors, so it is best to discard any dead plant tissue.
The dead leaves may have contributed to the soil staying moist, but I am quite sure you have been watering too often, in any case. D. Marginatas use less water as they age. That is why you are seeing mold in the soil. The presence of the mold also suggests that the potting mix your D. Marginata is in was not sterile. Nothing you can do about that, however.
The plant is still healthy, so there is a good chance that you have identified the problem early enough to keep your plant healthy. First, remove all debris and any loose soil from the surface that is not in immediate contact with the roots This will help air penetrate into the root zone more readily.
If you allow the soil to dry out properly between waterings, you will deprive any mold in the soil of the moisture that is essential to its growth. If you try to remove some of the soil, you will damage many of the tiny root-hairs that do most of the work. So leave the roots and surrounding soil alone. Needless to say, a larger pot with more soil will just keep the soil around the roots damp for even longer.
It is quite common for Marginata roots to coil in the bottom of the pot. It may look uncomfortable to human eyes, but the plant is quite content to have its roots in that condition.
Provide lots of bright, but mostly indirect sunlight and warm temps to assist in the drying out of the soil. Allow the top quarter of the soil to dry out before adding just enough water so that it reaches that level of dryness again in about one week. You will have to experiment a bit to determine just what the right amount of water that is. Be patient regardless of how long it takes for the soil to dry out.