Bottom Heat?

Wednesday, January 16, 2013
Bottom Heat and Breaking Rules Chinese fringe plants are hugely popular in many places because they are almost bulletproof. Heavy soil or sand, pretty wet or fairly dry, full sun or part shade, they grow and bloom. The biggest issue with this gorgeous group is their way of growing beyond all proportions. The tag may say, “easily maintained at 4 feet tall” but I hope you are going for 6 feet and almost as wide or you’ll be pruning constantly. I knew the shocking pink flowered lorrie shown here would be a big sucker and enjoyed turning it into a treeform. But now the canopy keeps getting taller on me and it is, yes, out of proportion. In bloom at Thanksgiving, it reminded me of a turkey: massive on top with skinny legs. When I visited a home in Holland with a quarter mile of perfect myrtle hedge, I had to ask how often the avid gardeners pruned it. The answer didn’t surprise me – it takes a full day every other week for six months a year to keep it all in sync. I am not a constant pruner but something needs a clip most every month in my Zone 8 garden. I cannot help the sense of waste if I burn or compost healthy plant material and must try at least a couple of cuttings. Since not all of these pruning jags goes by the calendar, my habit leads to rule breaking as I try to root “wrong” woods at the “wrong” time. I have stuck cuttings indoors and outdoors, in garden soil and in rooting media, with powder and liquid rooting hormones of different strengths. Nothing has made as much difference in my efforts as bottom heat. I first encountered a heating cable when my job was to monitor its temperature. It was a snake winding its way through rooting media in a huge wooden box under a greenhouse bench where I worked. With a soil thermometer and a clipboard, I recorded daily and it never missed despite being 10 years old. I don’t know, but there’s probably an app for that now. I liked the idea of the heating cable and it worked well, but didn’t enjoy cleaning it when refilling the rooting box. Soon enough I found heating mats and have used them ever since. When shopping for either kind of soil warmer, look at its measurements. Cables will be calculated in square inches with layout diagrams in most packages while mats come in several standard sizes. I like to fill pots or flats with damp rooting media and put them on the mat for 24 hours before sticking the cuttings. It probably doesn’t matter but I keep my plant room air temperature cool and want to avoid soil conditions that might be cool and thus promote fungus development. No matter what time of year it is, I find wood in these prunings that is bendable and some that is hard and I try both. I have stuck cuttings of fringe flower from every kind of wood except very soft new growth and, not surprisingly, this vigorous shrub roots anytime. I take tip cuttings 6 inches long, roll the base in Hormex #3, and stick one cutting in a 3 inch pot so 2 inches of stem is below the soil. Camellia sasanquas can be problematic since they bloom in autumn and pruning more than a month later can cut off next year’s buds. The rules also say that a flowering branch will not root but I have clipped off six inches of stem, removed only the tip and old flower and had success. I was pressed into this way the year I pruned sasanquas for a client with 3 varieties that I wanted to clone. Bottom heat and Hormex #3 made it happen in a flat filled with ground bark and sand. I worked at an office that was expanding that summer and had two problems. There were 10 huge yaupon hollies that would badly overpower the new entrance but removing them was not an option. At the same time, the new parking lot would need a windbreak soon. I cut back the yaupons by half their size even though it was midsummer. That meant a loss of berries and very mature wood in the cuttings. Undaunted and no doubt full of myself, I decided to root foot long cuttings. Thankfully for my reputation, the combination of bottom heat, Hormex, and several applications of dilute soluble 20-20-20 fertilizer resulted in a 50 per cent success rate. Of course a mist system would increase my successes considerably but my little rig broke and I’m rethinking its design and location. Hmmm…send me your suggestions!
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