Seasonal changes are often so subtle that plants are more conscious of them than man.
In June the daylight hours are long. The sun with its warmth and the clouds with their moisture encourage plants to grow to their maximum heights.
There is seemingly no hurry about producing buds. Unwanted lambs-quarters (Chenopodium album) and pigweed (Amaranthus retroflexus) grow as high as the taller garden plants.
But when they come up late in the summer, they remain dwarf and commence to bud when a few inches high. Zinnia flowers planted in late June make buds quicker and on shorter plants than seeds sown in May.
Seasonal Changes Affect Plants Differently
These seasonal changes do not affect all plants in the same way. If they did, all our bulb flowers might bloom in early spring with the daffodils or all our perennials be covered with blossoms in iris time – the weeds might all be flowering in late summer with the goldenrod.
Plants from tomato seeds planted in May have ripe tomatoes in July and August. If only the number of days counted we should be able to plant tomato seeds in January and have ripe fruit in a sunny window in March or April.
The winter-planted seeds, although they may germinate satisfactorily are slow to make growth and seem to stand for days without any noticeable change in size.
They often wait to develop blossoms until the longer days of summer.
Short Day Plants
On the other hand the short day plants such as poinsettia may refuse to bloom if they are kept in a room where lights are on each night. They require a long night in order to make buds.
We are advised to set the plants in a dark closet at night or to cover with a black cloth if kept in a room where lights are on even for a little while. There are exceptions to every rule.
Let me add that if your poinsettia blooms well each winter in the family living room uncovered with lights on at night – then continue the same way. But if your plant refuses to bloom under these conditions, then provide it with a short day and a long night to see if results are better. The same system will work with Christmas cactus.
Mums are short day plants. They wait until the shorter days of late summer and early fall to set buds. There are varieties that bud in July but many wait until the days are much shorter and then frequently the frost gets them before they open.
For these slow ones, a wooden frame can be built and covered with a black cloth to make it as lightproof as possible.
Starting about mid-July, set the frames over the mums at five in the afternoon and remove at seven the next morning.
This will artificially shorten the daylight hours and lengthen the night hours, thus causing the plant to hurry along with its buds. Discard the frame when the buds show color.
Growing Under Lights
When growing plants under lights, the hours of light and darkness can be regulated.
Such things as African violets and dwarf geraniums requiring long days are left under the lights for 14 hours. Christmas cactus, freesias and poinsettias requiring 14 hours of darkness can be removed to a dark closet at five or six o’clock at night and put under the lights again around seven the next morning.
It is tantalizing to have plants behave in such different ways – some require short days and others long days in order to bloom.
Some go dormant early in the season, and others are so slow their buds are frozen – but we know it to be true even if we cannot explain why.
Note the blue baptisia (Baptisia australis) that comes up early in the spring and blooms in May. Then observe the white one (Baptisia leucantha) which doesn’t so much as yawn until the blue one is blooming.
We must mark its place well in order not to hoe off its nose while still asleep.
Best Times For Propagation
There’s the matter of trying to root leaves or cuttings at any time of year.
They may root readily and grow beautifully in the spring and simply rot or take forever to root during the short, dark days of winter.
Whether it is day length or something else that causes these things, it is well to be aware of the fact that the length of light and darkness may be causes for failure or reasons for success instead of the color of our thumbs!
Temperatures and Plant Growth
Temperature, too, affects plant growth and flowering. Some plants want it cool, some want it hot.
In the Midwest where corn is an important crop, it is necessary to have hot nights.
The nights almost unbearable for sleeping are the nights when you can “hear the corn growing!”
Have you observed Hemerocallis (Daylilies) on mornings after cool nights – how slow they are to open? They like good corn-growing weather, too.
Strawberries like it cool. The season is much shorter and the berries smaller during an abnormally hot spring than during a cool spring.
Don’t Forget Moisture
Moisture is another factor you cannot overlook.
The rain-lily (zephyranthes) is a startling example. The flowers appear almost overnight as soon as a rainy season starts.
Hardy amaryllis (Lycoris squamigera) can be hurried into bloom by soaking the row several weeks before their normal blooming period.
Some cut flowers can be regulated. Should you need peonies several weeks later than their normal blooming period, cut the buds when they show good color, place them in plastic bags in the refrigerator.
Get them out the night before you want to use them. Cut off a bit from the end of each stem and put them in water. Narcissus and roses cut in the bud stage can be kept the same way. Use hot water to freshen the roses. Cut lilies-of-the-valley when three-fourths or more of the blossoms have opened.