March 25, 2013

Root Zone Heating? in Florida ?

Electric propagation heating mat
courtesy of Thompson and Morgan
 Root zone heat can dramatically improve rooting and seed germination, yet few people use the technique very much these days. It is a tried-and-true technique, but I believe most growers in Florida feel it is unnecessary, given our abundant heat most of the year. It is the temperature difference from day to night which makes such a difference in rooting plants or germinating seeds. Even though we might have a 90 F day, sometimes the temperatures go down to 75F at night, even cooler in the Spring and Fall weather changeover. If we can stabilize the temperature difference from day to night to just a few degrees, seeds sprout faster and cuttings root stronger.

sealed polymer heating and propagation mat
courtesy of Growers Supply

Victorian-era greenhouse gardeners often used paraffin oil burners underneath metal clad seed beds to boost root zone temperatures, and many temperate-zone gardeners have long used root heating mats to keep plants healthy. There are many ways to stabilize and boost root zone heating, many of which are easily available from garden supply firms. Styles range from slender heating cables to be buried in soil or sand, to wafer-thin sealed polymer mats to hefty swine heating mats capable of handling foot traffic. Most of the higher-cost heating mats require the use of a thermostat to regulate the temperature, some of the basic ones are pre-set to 74F. In areas where the growing area temperature is very cool, 74F would be suitable; for our needs with tropical plants, 78-80F is preferred. 

a basic, single-zone controller
courtesy of

It is surprising how well plants will respond when their roots are kept warm, especially in the shorter days of the year. Tropical plant seeds and seedlings especially like to have warm root zones; their genetic world is made up of stable temperatures with little difference from day to night. Many palm and cycad species will grow far better and will have fewer diseases with root heat in the cooler months.

Kane brand pig warming mat
courtesy of QC Supply

One of the simplest techniques seen on the Internet is to use an old water-bed heater, placed under a large mortar-mixing tub of coarse sand. Seeds, cuttings and pots can be stuck into the warm sand, the improved growth results are worth the effort. This technique is the modern version of the Victorian-era tactic of placing paraffin burners under a metal box full of compost. Try heating up the roots of your sensitive plant species a few degrees, and watch the results. The difference is remarkable. 


multiple-zone propagation mat controller
courtesy of 4 Hydro

 Craig Morell
Pinecrest Gardens


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