Spring has finally sprung. It’s the day of the vernal equinox, 20th March here in the UK. It is such a crucial date in the gardening calendar, this is the time that night and day become equal. There is a slight discrepancy which is due to various astronomical reasons which I will not bore you with right now as the most important thing to remember is short winter days are disappearing and the long days of summer are on their way. You will begin to see a surge of growth and activity from plants in the garden and seedlings sown earlier in the year as many plants respond to the lengthening of days of spring and the shortening cooler nights very well. It is such an important response that it has its own name, photoperiodism.
Each plant has its own inbuilt regulated response to the length of day and night. Some plants like more daylight hours, some less and others like equal length so these form 3 distinctive groups. Short Day plants, Long Day plants and Day neutral plants. Short day plants will flower best when day lengths are below a certain number of and vice versa for long day plants. Day neutral plants will flower when they are ready and are not really affected by light so much.
Short day plants : Chrysanthemum & Dahlias tend to flower later in the season, during late summer and autumn as they do not like long sunny days and prefer longer nights.
Long day plants : Foxgloves, Hibiscus & Gypsophilla like to wait for longer daylight hours.
Day neutral plants: Viburnum, radishes, tomatoes & strawberries will flower when they ready.
Horticulturists and home gardeners can of course use artificial lights and controlled environments to manipulate the day and night length and increase the growing season. Daylight lamps will force rapid growth in seedlings but the cost of this to the home gardener usually outweighs any benefit on such a small scale.
However in late spring and early summer it is much easier to shorten daylight hours on flowers for instance Chrysanthemums naturally bloom with the long nights of spring or autumn. By making the days shorter by covering them for at least 12 hours a day over the course of several weeks in late spring/early summer you can stimulating blooming.
Taking photographs and record notes for where sun lies in your garden at the equinox and which flowers are in bloom is a great to refer back to year after year when planning your garden.