Autumn is upon us with the equinox tomorrow – 23rd Sep.
It is such a crucial date in the gardening calendar as this is the time that night and day become equal and when the sun crosses the equator from north to south. There is a slight discrepancy which is due to various astronomical reasons which I will not bore you with right now.
The most important thing to remember is that the longer summer days are ending and the short days of winter are on their way. You will begin to see a slow down in growth and activity from plants in the garden and seedlings sown earlier in the year as many plants respond to the shortening days of autumn and the long dark nights. It is such an important response that it has its own name - photoperiodism.
It is important for plants to know the difference in seasons as it just would not be productive to flower when there are no pollinating insects around. This also ensures that they do not allow their seeds to germinate during the winter time as this would surely kill small seedlings off. Some plants and their seeds lie dormant over the winter time but need period of cold & frost to encourage germination and growth. Plants & seeds can be artificially chilled to stimulate flowering in Spring.
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.