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Cloning Wars Part 2

(An abridged version is found in the March 2011 issue of Maximum Yield.)

Cloning Wars Part 2: Dense Matrix LED Technology Takes Root

Brian Chiang and Josh Puckett

There's no question what Dense Matrix LED technology is capable of. With its growing presence in the indoor gardening industry, LEDs boast energy efficiency, long lifetimes, and more importantly, they can produce specific spectrums optimized for plant growth. After years of research, scientists have discovered various wavelength combinations for vegetative growth in addition to ideal wavelength blends for fruiting and flowering. Indoor growers everywhere are benefiting from the ability of LEDs to emit specific spectrums.

The advent of dense matrix LED technology, which compacts many LED chips into a single point source, offers more than long lifetimes and energy-savings. This platform is able to unite multiple wavelengths to produce one uniform spectrum that not only eliminates sporadic hot spots, but also allows the entire spectrum to penetrate deeply into plants. This capacity gives assurance to both indoor growers and researchers alike, as dense matrix LED products are used in more applications than just during the vegetative or flowering phases of growth.

Rethinking Light Spectrum and Plants

A large portion of how plants perceive their environment and the passing of time is through the reception of light. Throughout evolution, plants have developed pigments and photo-sensory complexes, which allow them to detect the quality and quantity of light they are receiving. These biological mechanisms often trigger hormonal responses that communicate to parts of the plant whether they should grow longer, initiate flowering, generate roots, etc.

Most growers are familiar with plant groupings that include sun loving, shade loving, and more. These terms describe plants by their intensity requirements, or the quantity of light they need. With the advancement of LEDs, we're beginning to see a shift toward describing plants by their spectral requirements, which, like light intensity, vary amongst plant species and varieties. Spectral requirements not only include ideal wavelengths, but also the quality of light needed. Individual plants require different spectra and intensities throughout their lifecycle.

Although it is currently difficult to make broad assertions on spectral requirements, we are researching plant reactions to light spectra and intensity amongst different species. The versatility of LEDs to define light spectrums makes this technology the perfect medium to find optimal wavelength combinations for different plants throughout the growth cycle.

We've seen positive results from vegetative and reproductive tests using dense matrix LED grow lights, and our research has developed from this success to include experiments on plant steering, cloning, and more. Last month, we described the initial results of wavelength testing on root formation from propagated cuttings, or clones, and though dense matrix LEDs were successful in promoting roots, it was unclear which spectrum proved most effective. We continued our rigorous testing and experimentation with herbaceous and dormant hardwood cuttings of different plant species using various wavelengths of LED light.

Initial Experiments: Husky Red Cherry Tomatoes

As a recap of our initial experiments, we previously cloned Husky Red Cherry Tomatoes using green cuttings without using hormones. The results are based on observing the days until callus formation, root formation, and root branching that occurred amongst the cuttings. At the end of each experiment, percentages of these parameters were taken in addition to wet and dry weights of generated root mass.

To determine whether the presence of light played a role in hastening rooting or increasing the amount of produced root mass, tests were done comparing groups subjected to high intensity LED light and complete darkness. Tests were repeated numerous times to confirm results, each time confirming that green tomato cuttings root faster and produce more root mass when light is present.

Next we compared the role of light intensity upon rooting in herbaceous cuttings. We rooted fifteen terminal and axillary propagations in cloning units subjected to different intensities of light. The number of dense matrix LED grow light units that were suspended above the cuttings controlled the difference in intensity. From these tests we confirmed that green tomato cuttings do not require high intensities of light to generate sufficient root mass quickly. There was little difference in quickness of rooting and biomass production amongst the groups.

Having observed that light intensity, except in extreme excess and deficiency, does not critically affect the rate and amount of root production, we focused our efforts on identifying wavelengths and spectra that do. We rooted fifteen terminal propagations in cloning units under different wavelengths of light and observed the differences in rooting. Original trials tested green, blue, red, and purple dense matrix LED units (mixture of red and blue wavelengths) as root promoting light treatments.

To eliminate the possibility of data corruption due to differences in cloning units we repeated these tests multiple times over. Cloning units were thoroughly cleaned, and unit components were switched before each trial. We maintained uniformity by matching each cutting's stem length, stem width, leaf number and number of nodes to eliminate possible bias from cutting size and origin on the mother

The majority of our trials demonstrated red to be the best light treatment for producing the most root mass in the herbaceous tomato cuttings. We recorded the longest roots with the highest percentage of branching in cuttings under the red LED treatment. Both wet and dry weights of root mass were the highest in this group after two weeks. Outside comparative tests done by industry representatives confirmed these results.

Secondary Experiments: Marianna Plum Rootstock and Dr. Huey Rose Rootstock

To verify our initial observations, we ran secondary tests, analyzing how isolated wavelengths and wavelength mixtures affect root development in propagated cuttings. While herbaceous tomato cuttings produced the most root mass under the red LED light we wanted to analyze whether this was true for different plant species.

Our secondary tests also used dormant or hardwood cuttings instead of herbaceous cuttings. Since dormant cuttings take longer to root, performance differences under each wavelength will be accentuated. It is also easier to maintain uniformity amongst the rooting plant material with dormant cuttings.

Dr. Huey Rose Rootstock

Using the same cloning units, we rooted fifteen dormant 9" Dr. Huey Rose rootstock cuttings under red, purple, and blue LED light. As before, we recorded days until callus formation, root formation, and root branching amongst the cuttings. We additionally recorded the days until bud break and compared vegetative production with root production. At the end of the experiment, percentages of these parameters were also taken in addition to wet and dry weights of generated root mass.

As before we observed the most significant root production in those cuttings subjected to the red LED treatment. These cuttings produced the longest roots with the highest percentage of root branching.

What was interesting to note in this experiment was the difference between callus and root formation amongst the treatments. The cuttings under purple and blue LED light produced considerably more callus, while the cuttings under red LED light produced significantly more roots. In addition, the bud break and vegetative growth of the cuttings under the purple and blue treatments was significantly more than those under the red treatment. Further research is required to investigate any correlation amongst these observations.

Marianna Plum Rootstock

We approached the Marianna rootstock cuttings using a different cloning method. We filled a 2'x3' ebb-n-flow tray with perilite and 6"cuttings were placed into the tray. Suspended above the cuttings were red and blue LED units. The tray was on a timer set to flood twice daily for five minutes.

Through this experiment we confirmed that our observations in the previous trials were not the result of variation amongst the cloning units. As before we observed increased production of root mass in those cuttings rooted under the red LED. The percentage of root branching was also higher amongst those cuttings under the red LED treatment. While we did record higher rooting percentage in the cuttings under the blue LED treatment, the amount of roots produced was inferior to those rooted under red LED light. Trials of this experiment are currently being repeated.


Though we are continuing our research, our current results indicate a correlation between root mass production and red light amongst propagated herbaceous and dormant cuttings across a variety of plant species. Red light seems to promote root elongation as well as root branching in cuttings despite different methods of rooting.

The flexibility of LEDs to produce specific wavelengths, and the advancement of dense matrix LED technology that compacts these wavelengths to create spectrums is revolutionizing the indoor growing industry. By providing spectral variation, growers can choose the best spectrum for various species and different phases of growth. The capacity of dense matrix LEDs to emit these spectrums is increasing our knowledge of plant light requirements by giving researchers the tools to investigate wavelength driven plant responses. With this understanding, and as LEDs continue to expand lighting applications, we will be able to fully transform how we garden indoors.