Pierre, here in the inland Southern California areas, which are more savannah-like, Banksiae flowers for maybe a few weeks. Closer to the coast, where the “hot” weather holds off for many more months, they flower repeatedly. Apparently, it’s the heat which triggers the flower repressor genes in them.
The farther inland you get from the ocean, the more extreme the temperature changes, both from night to day as well as month of the year. Along the coast, in many places, the most extreme the temperature differences between night and day is usually within twenty-five degrees. Often, it’s quite a bit less than that. Those more “spring-like” temperatures and light levels can continue from “winter” all the way through late August to September, when it begins to really heat up for a month or two.
To contrast, one mountain range inland, as well as higher up the mountains from the coastal areas, there can often be up to a fifty degree increase in temperature, with much less fog to soften the light intensities. Currently, the temperature difference between the coastal areas and where I am is between ten and fifteen degrees for day-time highs. By June, this can easily stretch to twenty and more daily. Nights are usually ten degrees warmer here during summer, and up to twenty degrees colder in winter.
Along the coastal areas, Banksiae can begin flowering in January and February and I’ve seen it continue until well in to July. Mine here in Encino, just over the top of the mountains from the areas where they can flower for six months and longer, began nearly two months ago and are still loaded with buds. The double yellow out front caps a large stand of Golden Bamboo, growing up through it and using it for support. This one receives sun all day long, with much reflected heat and light off the white styro foam roof. The bamboo causes it water stress as well as transpiring tremendous levels of moisture underneath it and through its mass. This one can spasm flowers just about any time of the year and it is nearly constantly mildewed.
Beneath and below the deck on the south-western corner of the house in the rear is a huge double white. It flowers later than the double yellow which is just across the deck, garage and apartment from it. This one has no other plants close enough to it to produce the humidity to induce the mildew, and it is often as dry as the one in the bamboo as the only irrigation is rainfall and when I happen to feel I want to hand water it with the hose. This dry corner is significantly hotter than where the double yellow is, but receives only two-thirds the direct sun the double yellow receives. Both grow rampantly, but the white begins flowering weeks later, having been in bloom now for about a month. The lutescens is still potted in a twenty gallon squat and hasn’t begun setting buds yet. It also receives filtered sun through a California Black Walnut until mid afternoon, when it receives full, direct sun from the due west exposure.
Vina Banks is planted out to the west of the double white on the hill and has popped flowers much of the winter and still has some today. There is a Purezza in the front walled garden I’m hoping will spill over the front wall. It doesn’t have as much reflected heat as there is climbing fig on the wall which softens the reflected heat. This one flowers mainly when our temperatures are well into the eighties F for extended periods. The canned Purezza (still waiting to find a home in back), is shaded by the Walnut and has thrown a few flowers but nothing like what I expect when it gets hot. Right now, we’re in the mid seventies, but have had several spikes to the mid eighties in the past three weeks.
By September, there can easily be up to a fifty degree temperature difference between the coast and right here, with several degrees even hotter as you travel further inland than I am. I’ve left work right on the ocean on Labor Day (early September) where it was very foggy and sixty degrees F. Within five miles, it was already in the mid nineties F. By the time I had driven to the center of the valley I live in now, it was 115 F. Fifteen miles further, at home, it was 119 F. Even just five miles up the moutain in The Highlands, in the same postal zip code, it can be fifty degrees hotter with no fog, while the bottom of the mountain is cold, damp and extremely foggy. This is considered “normal” for the area.
In that fog belt is where the Banksiaes continue flowering well into the year, unless the weather turns hotter, earlier, when they cease flowering. Mine begin weeks later and are usually finished when the heat begins, months earlier than along the coast. In the Santa Clarita Valley, the next valley inland from here, they are finished months earlier than even here, because the heat has usually already started intensifying and remaining hot.
I’ve seen the same performance from the hybrid Hulthemias, Nigel Hawthorne and Euphrates; R. Arkansana “Peppermint” and O’Neal Blueberry to remember a few. On the edge of the fog belt, I had a client who planted many O’Neal Blueberry because her four year old daughter loved them. Those bushes began flowering in January (as mine are here, now) and continued to flower and fruit until mid September, when her garden got “hot”. The roses came from Ashdown and were budded on R. multiflora, canned and sold where I worked. The same varieties from the same source, performed here as expected, as does the O’Neal Blueberry. Though, one block from the ocean where it was colder, extremely damp and heavily foggy much of the day and where the temperatures remained in the low to mid sixty degree range, the three roses mentioned above and the Banksiaes, began flowering earlier and continued until at least late August when it heated up that year. Nigel Hawthorne continued one year until mid September, as did the Banksiaes, as it got “hot” there later.
That all leads me to feel it is temperature induced, whether it is just the heat level, or the extremes between high and low temperatures, I don’t know, but “hot” seems to turn off the flowering in the traditional Banksiae, the roses mentioned earlier and the blueberry. Eucalyptus begins flowering in the fog zone weeks earlier than here and continues a good month later, also depending upon how hot it gets, how early it happens. Vina Banks and Purezza require the heat to begin and continue flowering. In the chillier zones, they can begin flowering once there is sufficient heat, but stop until the much hotter weather begins. Once, I’ve been told the Purezza out grew that performance, beginning to flower when expected and continuing to repeat, even after traditional Banksiae have stopped. Inland, where it’s hotter, Purezza begins usually when the traditional Banksiaes stop and continue flowering heavily as long as the weather remains at least in the high eighties F. Kim