Happy Valentine! 14th February is traditionally the day that lovers exchange gifts, that the birds start making their nests and, as I’ve only recently found out, a really important day for the rooftopvegplot.
Most books will tell you that plants need ten hours of daylight in order to start into growth. Coincidentally that critical event will occur over the next few days. The ten hour day will reach Plymouth on Valentine’s Day, with 10 hours and 2 minutes of daylight. On 15th February London will click into the ten hour zone and by February 19th the shadow of the sun will be cast for ten hours over Newcastle.
So perhaps it isn’t a coincidence that springtime’s love-in is set at this time of year. Animals as well as plants are sensitive to light levels. Butterflies and squirrels come out of hibernation when the day length increases. Birds will start to make their nests; why not humans too? My Valentines gift to the birds will be a wool-stack, a collection of off-cuts that they can use to make their nests cosy.
I always feel that mid-February is the very pit of the winter season. At the moment spring seems a long way off. But on February 14th we gardeners have a lot to celebrate, because it is not only day-length that will be changing fast over the next few weeks. The sun will rise higher day by day, leaping a massive ten degrees higher in the sky by the end of the month. And in addition, the sun’s rays will start to get warmer as they have to travel through less atmosphere in order to reach us.
This time of year everything gets a fillip from the double bonus of longer days and the higher altitude of the sun. Every gardener knows that plants get their energy from the sun. It is photosynthesis that allows plants to break down carbon dioxide into sugars that form the cellulose of plant matter and to exude oxygen that is the stuff of animal and human life. No amount of fertiliser will change that fact. But the measure of a plant’s ultimate success is neither the hours of sunlight, nor the altitude of the sun. Those two factors both play their part, but it is the amount of energy that the sun provides on a daily basis that is the most important factor in plant growth.
The sun’s energy can be measured as it shines onto a plant, in a very similar way to gauging the energy that falls onto a solar panel. In January that sunlight energy is tiny. Clouds, low sun and the long dark nights all play their part. But as February turns to March, and March turns to April, there is a steep rise in what is called insolation, the amount of energy that the sun provides.
To give you an idea, a three foot square bed of lettuces will receive less than half a kWh of heat energy on a typical January day, but by the end of April that figure will have risen beyond four kWh. i.e. the energy those lettuces will have to convert into nice fresh leaves will have risen eight-fold. By the end of May we will still be a few weeks away from mid-summer. It may get hotter beyond that time, but for most of the country the end of May represents the highest insolation levels. Once those energy levels start to die down, plants like lettuces, that are light sensitive, start to prepare for winter by going to seed. Most books will tell you that this is triggered by the passing of mid-summer. I don’t believe that. I think the plant is more sensitive to the total sunlight energy that it gets, rather than to the height of the sun. So I always start to watch out for plants running to seed a full month before mid-summer’s day. Here is the graph that illustrates the whole thing.
There has been a lot of discussion on Twitter over the last week about what should be an appropriate present for Valentine’s Day. I’m now much more aware that British flowers grown in our most favoured counties can be wonderful now. So if you are going to give flowers please give British flowers. Take a look at Sara Venn’s (@saralimback) blog http://www.thephysicblog.blogspot.co.uk/2014/02/britishflowers.html
And there is still time to order, or to find a local florist that stocks these flowers. Here are some links to British growers that I've got to know via Twitter.
@BritishFlowers greatbritishflorist.co.uk Heather Gorringe Duchy Estate in Herefordshire.
@wildflowersuk http://www.wildflowers.co.uk/
@theflowerfarmer http://www.commonfarmflowers.com/ Georgie Newbery
@myflowerpatch Sara Willman
@thepatientmole Gill Hodgson fieldhouseflowers.co.uk
@bareblooms bareblooms.co.uk
(Happy to add others here if they leave a comment at the end of this blog.)
Like spring flowers, many of my most favourite vegetables are light sensitive. i.e. they won’t start into growing until they get enough light. That’s why the advice is always to select the sunniest spot in the garden for your veg plot.
This week I shall be starting on the spring bed. That is my sunniest bed. It lies directly adjacent to the sitting area, so it’s the one that I always want to look nice as early as possible in the year. The hyssop edging is already in place. This is a very low clipped hedge 150mm high that keeps a bit of wind off the bed. My colour scheme for this bed is pale as can be, just white and lime green with the odd splash of lavender and burgundy. I already have a miniature rose and a clump of dark perennial poppies. Species tulips are allso showing through. My planting scheme for the spring will include lime green lettuces, pale chicory, chervil (which will produce delicate bracts of white flowers by summer) and a clump or two of red basil.
I shall work with the seasons to draw a good leafy crop from this bed through March, April and May. By June, just when the British flower season will be at its height, the lettuces might have started to go to seed. I shall leave some of them, just for the beauty of their flowers (and to collect some seed). By then I shall have planted legumes and sweet peas on the trellis at one end of this bed. The full trellis provides more shade over the hot months of July and August. This should allow me to grow different lettuces once I’ve harvested the spring varieties.
For me Valentine’s Day is an affirmation of summer yet to come. It should be an optimistic time, looking forward to the life that is not yet known. Whatever you do on the 14th February, please take a moment to look towards the future. This ghastly winter will be over very soon. By the time spring finally comes, winter's passions will be spent.
