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November 28, 2010

The Importance of Daylength and Light

EVERY FALL, I BLEACH THE TEAK POTTING BENCH IN THE BACK OF THE GREENHOUSE, TO KILL ANY BACTERIA AND FUNGUS, IN PREP FOR THE COLD, DAMP CONDITIONS OF WINTER. DAMP POTTING SOIL AND WET CLAY POTS CAN EVEN ROT THE MOST TROPICAL OF HARDWOODS.

As winter approaches, the low angle of the sun and the short days and long nights, make every minute of sunshine, precious. Grumble, as we may about these long nights, without them, many plants will not form buds on schedule. I get asked so often about how I get certain plants to bloom which are notoriously shy about blooming as houseplants, and all I can say is that now that I have a greenhouse, I really don't think about this challenge anymore. There was a time when every October, we would moves the large pots of Christmas Cactus, Poinsettia and Clivia into the dark, cool cellar for a month, to 'trigger' bud formation. A move that rarely seemed to work well. But once we built the greenhouse, every plant blooms on schedule, give or take a few weeks.

 I can look back every December on this blog, and see that my Haemanthus should be in bloom this week, (and it is). Clearly, day length is critical, and I would venture to say that it, along with temperature shifts, are the key triggers for bud formation with many plants. It does make one wonder, do humans respond to seasonal shifts in temperature and light? I mean, beyond the known benefits of light exposure ( which, I must admit, a sunny day in a winter greenhouse does wonders for those suffering from seasonal disorders, which Joe has, and I think that I do not). But I wonder if there are any other benefits from humans being exposed to natured elements that we not miss in our climate controlled homes?

AS YOU CAN SEE, THE FALL CAMELLIAS ARE STILL BLOOMING, AS IS EVERYTHING ELSE THAT SHOULD BE BLOOMING RIGHT NOW. THE ZYGOCACTUS ( CHRISTMAS CACTUS). WHEN GROWN UNDER GLASS, THIS PLANT RESPONDS NATURALLY TO THE SHORTER DAY LENGTH AND IT FORMS FLOWER BUDS WITHOUT ANY 'CELLAR TRICKS'. EARLY NARCISSUS ARE BEGINNING TO BLOOM, TOO.

EVERYTHING HAS A SEASON, AND POINSETTIA BLOOM NATURALLY IN MEXICO FROM AROUND CHRISTMAS THROUGH  JANUARY.  THIS WILD SPECIES FORM IS JUST STARTING TO FORM THE PLANTS ICONIC RED BRACTS.

The Poinsettia we see at the supermarkets are artificially subjected to short daylength periods earlier in the season ( draped with black plastic).  At home, it is almost impossible to get a plant to rebloom unless you are prudent about daylength ( even a streetlight or a lamp can throw off the photo period). The above plant I have is actually the wild form of Poinsettia, or EUPHORBIA PULCHERRIMA. As you can see, it is just starting to form colorful bracts, which is normal for late November. In the wilds of Mexico, where this plant is native, the same thing is happening. When I lived in Hawaii, I remembered old Hawaiian cottages that looked very much like New England cottages, but instead of blue Hydrangeas, red Poinsettias were in bloom in January. 

The plants we see now everywhere are not only hybrids, but drenched in growth retardant, which keeps them short enough for retail ( even shelves on shipping trucks are kept at  certain height to maximize profits). So good luck finding a tall, old-fashioned poinsettia unless you know of a good florist who grows their own ( rare these days). The wild form is weedier, but I am fine with that. My only concern is as the weather cools down, the greenhouse will start to stay at around 40 degree's which is too cold for this genus, which prefers to stay above 50 deg. F. So I may move this, and a tree aloe which is forming a bud, into the studio for the winter, to see if that helps.


Speaking of light quality, I try to keep single pane glass as clean as possible, since I believe that light quality in winter, is one reason why I have good results with some of my winter growing bulbs. Since I must use bubble wrap insulation on the roof, my greenhouse is constructed with single pane glass, which may see very impractical given that I live in Massachusetts and winter temperatures can reach well below zero degrees F. for a couple of months in the winter. You may notice that many nurserymen and wholesale growers use poly hoop houses, those greenhouses that look as if plastic bags are stretched over hoops. These are usually inflated, with fans blowing air between the layers of plastic, which forms an insulating layer between the freezing temperatures outside, and the warm air inside. With glass, heat passes through quickly, and with single pane glass, even more so.
BUBBLE WRAP IS USED TO INSULATE THE ROOF. IT TAKES ME ABOUT 3 WEEKS TO GET IT UP SINCE IT TAKE AN ENTIRE DAY TO CREEP ALONG THE TOP BENCH WITH DOUBLE STICK TAPE IN HAND, SINCE IT IT 16 FEET HIGH OFF OF THE GROUND. BUT ON A SUNNY, COLD DAY, IT CAN BE 80 DEG. F UP IN THE PEAK, SO TANK TOPS AND BATHING SUITS ARE USED, WHICH IS RATHER NICE ON THE LAST WEEKEND BEFORE DECEMBER.

Still, I prefer the single pane glass for both aesthetic reasons and for the light quality, since South African bulbs require almost desert-like sunshine in the winter. So although I may tape bubblewrap insulation on the roof, I leave the front of the greenhouse un-insulated. I sited the house by looking where in our yard, the sunshine still hit on the shortest day of the year, so even though we have very tall trees, I can still get 7 hours of direct sunshine in the winter.
LIGHT QUALITY IS IMPROVED BY WASHING THE PANES OF GLASS ON THE SUNNY SIDE OF THE GREENHOUSE. IT'S AMAZING HOW DIRTY THE GLASS CAN GET. THE LOW ANGLE OF THE WINTER SUN AS WE APPROACH THE WINTER SOLSTICE MAKES EVERY STREAK NOTICEABLE, AND EVERY STREAK WE REMOVE, INCREASES THE QUALITY OF LIGHT.

Light quality is affected with poly film plastic, so even the bubble wrap is not ideal, but it helps me feel better about my propane bill! Since I keep many of the bulbs near the front of the greenhouse, I feel that if I keep the glass clean, the light quality is even better. Today, it was warm enough to wash the glass again ( I had done it in late August, but you can see how dirty it gets in just a few months!). It takes about three washings on either side to clean most of the streaks off, since  the low angle of the winter sun seems to pick up every streak.

WITH DECEMBER APPROACHING, THE BAY LAUREL STANDARDS HAD TO BE MOVED INTO THE GREENHOUSE. THESE ARE ALWAYS THE LAST PLANTS TO BE MOVED IN, AND AT 8 FEET TALL, THEY ARE THE HEAVIEST. THE BIG STRAWBERRY POT ALSO WAS MOVED INTO THE GREENHOUSE TO PROTECT IT FROM FROST HEAVES.

ONCE IN POSITION, THE DOORS CAN BE CLOSED FOR THE WINTER. ANNUAL TRIMMING KEEPS THE BAY LAURELS AT THE RIGHT SIZE, SO THAT THEY JUST FIT IN UNDER THE FURNACE WHICH IS MOUNTED NEAR THE CEILING.

OUTSIDE, THE BOXWOOD HEDGES ARE WRAPPED IN BURLAP, TO HELP REDUCE WINTER BURN.

THIS WAS INTERESTING. A POT WITH A PERUVIAN DAFFODIL, A SUMMER BLOOMING BULB THAT HAS GONE DORMANT WHILE SITTING IN ONE OF THE BAY LAURELS, SHOWS US HOW SOME BULBS ARE ANYTHING BUT DORMANT IN THE OFF SEASON. THE ROOTS OF THIS BULBS WERE RUNNING DOWN DEEP, AND IN FACT HAVE FILLED THE 8 INCH POT. 

I REPOTTED IT IN A 14 INCH DEEP POT, AND PLACED IT UNDER A BENCH FOR THE WINTER. THESE BULBS MAY BE SHIPPED WITHOUT ROOTS, BUT LIKE NERINE, THEY CLEARLY LIKE ROOT GROWTH WHEN THE TOP IS DORMANT.

1 comment :

  1. I love seeing the greenhouse full of bloom at this time during the year. So it helps Joe with seasonal light disorder?

    Hmm, maybe that is the way to sell it to my other half Jerry... I could tell him he could sit in there and get a tan while dreaming he is in some warm tropical island.

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