Plant Lighting For Dahlia Seedlings And Cuttings
Plant Lighting for Dahlia Seedlings and Cuttings
About this time of each year many a dahlia gardener decides to give it a go at planting dahlia seedlings or multiplying their stock by doing cuttings. By May, most of them are rather disappointed with the results.
For a number of years I personally struggled to grow good dahlia transplants from seed. They would come up, get reachy and flop over. I would pinch them back severely, they would struggle on and in May I would plant things that most people might consider discarding.
Eventually, I promised myself that I would raise my own good seedlings and I began a study of the subject. The key to my eventual success was a lot more lighting and this also proved to be a key to my later success in propagating dahlias from cuttings.
I did most of my research on the web and this is what I learned about plant lighting in general and dahlia lighting in particular:
1) Plants need light from both ends of the spectrum and reflect the middle range (green).
2) The red and far-red end of the spectrum helps plants mature, flower, set seed and fruit .
3) The blue end of the spectrum helps suppress the reaching (elongation) tendency in seedlings for 8-10 weeks.
4) Cool White fluorescent lights emit more blue than red and should be the lighting of choice for seed starting.
5) Light intensity is very important and should be in the range of 1000-3000 lumens per square foot depending on plant.
6) Light intensity of 2000 lumens per square foot is probably the minimum for good dahlia growth.
Since my practices of using commercial seed starting mix, bottom heating for germination and clear plastic tray covers to retain moisture seemed appropriate, I concentrated on correcting my apparent lighting problem.
This is what I did for less than $100USD.
1) I purchased a 4-shelf, 4ftx1.5ft steel shelving unit at an auction.
2) I attached TWO, 2-tube fluorescent light fixtures to the bottoms of EACH of the three upper shelves.
3) I purchased and installed 12 GE Residential Fluorescent tubes, which have replaced the traditional low priced Cool White shop lights. Advertised light output is 3150 lumens per tube x 4=12,600 lumens over each 6 square foot shelf or 2100 lumens per square foot.
4) I started raising stout and sturdy seedlings.
NOTE: The GE Residential tubes no longer carry a Lumen rating on the package and I find this a bit suspicious. However, I recently noticed that Home Depot sells a Philips, ALTO series Utility tube that indicates a light output of 3200 lumens. (For the record, most fluorescent tubes emit light in the 1800-2200 lumen intensity range.)