The croton reacts badly to changes in its environment, often losing most of its leaves. Photo: Rez, garden.org
Question: I received a 39-year-old croton this fall. It keeps losing leaves even though I placed it right in front of a big window. Should I give it fertilizer and, if so, what kind?
Answer: Your plant is not suffering from a lack of fertilizer, so no, don’t “feed” it (more on that later). It’s suffering from acclimatization shock, a very different problem.
The croton (Codiaeum variegatum) simply doesn’t appreciate changes in its growing conditions, especially when it’s a mature specimen. (Young crotons are easier to acclimatize.) This is doubly true when the move occurs in fall or winter, as in your case, because with reduced light due to short days and the dramatic drop in atmospheric humidity that occurs at that time of year, already just about all indoor plants are a bit stressed out and plants that are naturally poor at tolerating change, like a croton, find adapting even harder.
The leaves it bore when you brought the plant home had acclimatized to conditions that were certainly somewhat different. Your plant has therefore reacted by dropping them in order to grow new ones. However, under such circumstances, a mature croton tends to go overboard and lose so many of its leaves that it can longer long adequately carry on photosynthesis, in which case it may take years to entirely recover, if indeed it survives.
To help yours adapt, I suggest massively increasing the atmospheric humidity. At 90% humidity, it will be able to carry out photosynthesis much more efficiently than at 30%, even if lighting isn’t the best. You’ll find it will stop losing leaves very quickly once the humidity increases substantially
It’s pretty much impossible to increase the air humidity in your home to 90%… and you wouldn’t like it anyway; that’s too high for humans to feel comfortable. However, you can easily give your croton that kind of humidity by enclosing it inside a large transparent plastic bag (a bag recuperated from the cleaners or a transparent trash bag would be perfect). Or build a frame around it and cover the frame with sheets of transparent plastic. This will create an individual greenhouse where the humidity automatically will be very high.
Temporarily move the plant away from direct sun: the defect of an individual greenhouse is that temperatures inside rise terribly when the sun shines directly on it. You’ll be able to move the plant nearer to the window at the end of the treatment.
In other seasons, I would have suggested keeping your croton “under glass” for 3 to 4 weeks, until the leaf drop stopped, but since it’s winter, the plant will still undergo a shock when you remove the bag. So, just leave it its greenhouse all winter. In spring (mid-March, late March), when the sun becomes stronger and humidity in your home returns to a more normal level, gradually remove the greenhouse over a week or two so it can complete its acclimatization.
Note that you won’t have to water your plant much while it bathes in its extra humid environment. Indeed, possibly not at all. Yes, in a closed environment, plants can often go for months without watering. Only water if the soil becomes dry to the touch.
But will it be able to breathe sealed under plastic like that? Of course! Plants are the ultimate air recyclers, producing then using their own carbon dioxide and oxygen.
What About Fertilizer?
In your question, you asked about fertilizer, as if you thought that would help, but, in fact, applying fertilizer to a plant suffering severe stress will actually harm it. Fertilizer is not a panacea and should never be supplied to a plant that is struggling to adapt. Fertilizer is something you give healthy plants in order to improve their performance, not weakened plants that will have trouble absorbing it.
In addition, winter is generally not the right season to fertilize houseplants, even healthy ones. Instead, you would normally apply fertilizer to a plant when it’s actively growing, that is, in spring or summer. So, yes, you can fertilize, but not right away. Wait until you remove the plant from its greenhouse shelter in the spring.
Which fertilizer should you use? It really doesn’t matter! Plants are essentially indifferent to the multiple fertilizers on the market. They’re not really designed for plants, but rather to appeal to the gardener’s belief that plants have very specific fertilizer needs. (Read Plants Can’t Read Fertilizer Labels.) Just use whatever fertilizer you have on hand and your croton will be perfectly happy.
And also, it’s rarely necessary to fertilize a houseplant at more than a quarter of the recommended rate.
Once your croton has acclimatized to your conditions (and it’s surprising how well an acclimatized croton will do in almost all indoor conditions, even under poor light and relatively low humidity), don’t move it around. You can give it a regular quarter turn to stimulate equal growth from all sides, of course, but don’t move it another room or other location; otherwise you’ll have to acclimatize it all over again.
If you treat your croton correctly, it ought to thrive in your home for another 39 years!