Last fall I wrote in this blog about one of my favorite houseplants, Streptocarpus, which I recommended as “an easy, colorful, houseplant to grow.” Immediately after writing that column, I somehow killed almost every one of them in my house. Plus a few African violets.

What happened?! At this point, I'm not really sure, but I have a few theories. It all started after that fateful column, when – in writing that column – I learned that I had planted my Streptocarpus in heavier soil than they ought to be in. Streptocarpus belong to the Gesneriad family, which also includes African violets and Gloxinias, and they prefer rich, well-drained soil. So I decided to replant my Streptocarpus, plus a few African violets that had outgrown their pots, in soil that approximated the conditions of their native home. That was my first mistake – DON'T MESS WITH A HAPPY PLANT.

I attempted to provide what I thought would be better soil conditions by buying African violet soil and throwing in a few amendments. But all that was available in the local store was Miracle-Gro African violet potting mix, which describes itself as “feeding” plants for up to six months. I was concerned about the effects of additional, and perhaps unnecessary, nutrients on a transplanted plant, but went ahead and bought it. (Perhaps I should have been more cautious in light of potting mix's advertising – to the contrary, as we learned in our Master Gardener classes, we do not “feed” plants with plant food, but instead we fertilize them.) That was my second mistake – DON'T SETTLE WHEN IT COMES TO SOIL.

On the positive side, I used fresh, presumably sterilized, soil, and new, well-scrubbed, pots. Even so, after a few weeks, I noticed that my plants were drooping. The leaves were dull and limp, and some of the plants' stems were mushy. Over the next few months, the plants declined until I finally resigned myself to the fact that they would not recover and threw them out. This was especially disappointing because I generally have found African violets and Streptocarpus easy to grow and willing to take a measure of neglect.

I then tried to figure out what went wrong. One of the most common causes of houseplant death is overwatering. I have never before had this problem with my plants because I usually forget to water them until they are gasping for water and trying to drag themselves out of their pots looking for water. In retrospect, it is possible that, because I wasn't used to the new soil mixture, I thought that it was drier than it was (sometimes fresh potting soil isn't as permeable to water) and overwatered the plants. Or maybe I underwatered them. In my research after the mass demise, the symptoms of under- and over-watering can be similar (brown and wilting leaves), which isn't terribly helpful. That was my third mistake – DETERMINE IF YOU ARE OVER- OR UNDER-WATERING YOUR PLANTS BEFORE IT'S TOO LATE.

Too much fertilizer also can result in wilting, drooping, foliage. Perhaps the potting mix with its plant “food” was too strong for my transplants.

If I overwatered my plants, then they would have been more susceptible to pests and fungal pathogens, such as Pythium and other species. I never saw any pests, but I did notice that the stems turned mushy on some of the plants. This suggests that the plants suffered from a common fungal disease, crown and root rot, which causes the crown, stem, and roots of the plant to turn soft and mushy. This problem can arise when plants are watered excessively, have poor drainage, or are planted too deeply. It can be prevented by using sterilized potting soil mixes and clean containers, which I did.

I will never be entirely sure about what killed my plants. I had had them for several years, and they thrived and survived transplanting until this one last time. I am inclined to think that the problem was either overwatering or the potting soil, or some combination, that led to crown and root rot. Maybe. To be on the safe side and avoid further problems, I threw out the potting soil (luckily, it was a small bag) and the pots.

While it has been disappointing lose a number of my favorite houseplants, the silver lining is that I will get to shop for new ones!