Houseplants forum: Sick Dragon Tree...

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Aug 8, 2017 5:13 PM CST
About a month and a half ago, I got a dragon tree (dracaena marginata) with two trunks, the taller one about eight inches tall, with lots of leaves extending it up to maybe two feet high, and the smaller about two inches tall, with leaves that are smaller and still competing with the taller trunk's leaves (unless they're actually two plants, in which case... should I split them up?)

Anyway, for a month or so, it was fine, in the pot it came in. Then I repotted it into a larger, more decorative one. I had soil at home, so didn't buy any new soil, but it was very old, several years, and totally dried out. It was also covered in cobwebs, which at the time (I'm very new to this!) I thought were just spider webs.

Now I'm guessing they were spider -mite- webs, as the poor tree has a stubborn infestation. It lives right behind my computer monitor, and I see little bugs that look like individual pixels crawling across my screen, way, way too small to make out legs or features, just little moving pixels. I thought because they're back-lit, that I'd caught it early, so I gave it a couple of good sprayings with mild soapy water, left it on for half an hour, then rinsed it off, twice.

But they just keep coming, and now I think it's because the soil was probably also full of eggs. Leaves are dying rapidly, all chewed up, brown and curling on the ends, with yellowing tattered edges in places on the bad ones. There are also little white spots underneath the leaves, though I'm not 100% sure if those aren't just soap stains where they didn't quite get rinsed enough.

The first time I watered it after the initial replanting, the water trickled down the leaves and trunks (which I now know isn't a great way to water them, but it was fun--again, I'm new!). When it had dried on top, the soil was white everywhere the water had pooled, which I'm thinking was maybe washed-off webbing?

I'm kind of at a loss. Do these sound like spider mites? Is this a plausible scenario, for them to be dormant in dry potting soil for years, then come to life when it's moist, and start eating my tree?

Would just repotting with fresh soil, and washing it down to bare roots and rinsing it well, be enough? Or do I need to do more, like buy predatory mites, or horticultural oil?

I also have a sanseveria that lives a few feet away, that seems fine so far... but I'm worried about it. How far do spider mites migrate, if that is what I have? Should I do anything preventative to protect it, or watch for anything in particular? It's still growing fine, though it does have a few edges that look a little "chewed on", but only on the original leaves, some of which are scarred and torn, and one of which has a big crooked bend in it. New leaves seem pretty okay.
Name: Will Creed
Professional indoor plant consultan
Aug 9, 2017 6:44 PM CST
So many plant problems begin with unnecessary repotting or repotting that is done incorrectly.

Never use old soil for your indoor plants. It is often contaminated, as yours obviously was. It is unlikely that there were any spider mites living in the soil as they need live plant tissue to suck on to survive. Not knowing the origin of that old soil, it is not possible to say what kind of critters you have introduced to your home. The webbing in the soil may have been a type of soil fungus.

I suggest that you try to undo the damage by undoing the repotting that you did. I hope that you left the original soil and rootball intact and simply added the contaminated soil around it. If so, you should be able to easily, but gently, remove that contaminated soil. Then, put the original rootball back into its original pot or one that is the same size so you don't have to add any new soil. If some of the original soil has fallen away, then get a small amount of freshly packaged peat moss to fill in the spaces.

If you don't like the look of the original pot, then simply place that pot inside a more attractive planter that you like. But leave the roots alone. Washing the old soil away may seem satisfying, but it also washes away many of the tiny roothairs that do most of the work.

If there are or were spider mites on the leaves, then a thorough spraying with a soap solution usually does the trick if you were thorough. You don't need predatory mites or oil.

Snake plants are mostly resistant to plant pests unless you decide to repot yours and use contaminated soil.

Your Marginata does best in front of a sunny window. Allow the top quarter of the soil to get dry before adding any water. Separating the plants is not recommended.
Will Creed
Horticultural Help, NYC
Contact me directly at [email protected]
I now have a book available on indoor plant care

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