How to get Clerodendrum to bloom?
Q: My Clerodendrum thomsoniae is not blooming. Actually it is not doing much of anything except putting out weak growth and small leaves. I purchased this plant May 26. 2015. Over the winter it was in a heated sunroom, at night 60 degrees, where it received some direct sun from the skylights. I reduced the water to prevent excessive leggy growth. I don't see how this plant can take full sun or even part sun. Temps here in Raleigh NC are 80-85 degrees and 65-70 at night, at the moment. I figured I would gradually expose it to more direct sun after being in a sunroom but the leaves burn. I had this plant in San Jose many years ago where it did quite well, blooming with no special treatment. So thought I'd give it a try again. Any advice?
A: Clerodendrums are all time favorites, appreciated by both gardeners and house plant collectors, for their showy, fragrant flowers and very easy culture. When growing Bleeding Heart (Clerodendrum thomsoniae), a few things should be taken in consideration:
1) Temperature.Like most clerodendrums, this plant is semi-decidious outside of tropics and goes dormant in winter. It may lose some or all leaves if temperatures drop below 60-65F. It is not too cold sensitive, the plant can even take some light freeze. However when it is not hot and humid, it slows down metabolism. This means, water should be reduced during cooler months.
2) Light. This plant can grow in both sun and shade like most clerodendrums - this is the beauty of this genus. However like with all flowering plants, more sun promotes more bloom. In shade, it will grow beautiful dark green foliage (leaves will be bigger than in the sun) on the account of flowering; in full sun leaves turn lighter color and sometimes may even get unattractive "faded" look, but flowering will be profuse. Also remember that Arizona full sun is different than New York full sun. Here in Florida, Bleeding Heart can take some full sun, but if exposed to sun all day long, leaves often get sun burn.
3) Acclimation. Also called acclimatization - this is a process when a living organism adjusts to environment changes. Acclimation is always the case when growing plants indoors, even in a sun room. When Spring comes, and especially when we start taking outdoors those plants that have spent a few months indoors, light level increases dramatically, and this may cause leaf loss, and leaf burn. It is not necessarily a bad thing, it is just a mechanism of acclimation. Example: imagine yourself after living in a warm tropical climate, moving to a cold country. For a while your body will feel discomfort from "too much cold", while native residents may feel comfortable. We call it "My blood has thinned after living in Florida" - and this is a physiological fact. And vice versa, if you are a Northerner, moving to hot climate may be a challenge; it will take a while until you get used to hot and humid tropical summers. Same thing with plants: during cooler and darker period, their body (leaves and stems) becomes "winter type", with some serious chemical restructuring. Immediate environment change, like bright light and high temperature, causes a shock to those "winter cells", and as a defense mechanism, the plant gets rid of those useless "winter" leaves, replacing them with new "summer" leaves with completely new chemistry and metabolism.
From what you described, you know your plants, and you know what you are doing. You did everything right by reducing watering in winter and gradually moving the plant into brighter light. You still may see some stress, and this is normal. If you patiently keep changing environment slowly, eventually your plant will generate new healthy "summer" growth, it will also improve more vigorous root grown which will help the plant to establish better and to be stronger. You will see larger, thicker leaves, and definitely some flowers.
