Now is time to purchase those bulbs that will produce spring flowers.
Mid- to late November is the best time for buying daffodil, snowdrop, tulip, narcissus, hyacinth and crocus bulbs so they will have enough time for chilling to bloom in the spring.
While not all bulbs need to be chilled, it is necessary for bulbs that are native to colder climates. Bulbs native to tropical and subtropical climates do not require chilling because they do not regularly experience cold temperatures.
The chilling period is the specific number of days certain bulbs require.
Plants are smart and not easily fooled because they have evolved a system to keep from being tricked into thinking it is spring before it really is.
So the bulbs rely on chilling hours — the time spent at temperatures typically between 35 and 45 degrees for a specific period. If you’re wondering how plants tell time, the answer is sugar.
Research shows that plants have a 24-hour clock known as circadian rhythm, just as we do. Our circadian clock is controlled by our brain and our genes in response to light. Ultimately, light or the sun is what drives plants as well.
Scientist Alex Webb found that sugar levels in a plant play a vital role in synchronizing circadian rhythms with its environment. Inhibiting photosynthesis (the process where plants harvest energy from the sun to make sugars for energy) slowed the plant’s internal clock between two and three hours.
Another scientist, Mike Haydon, explained: “The accumulation of sugar within the plant provides a kind of feedback for the circadian cycle in plants — a bit like resetting a stopwatch. We think this might be a way of telling the plant that energy in the form of sugars is available to perform important metabolic tasks. This mirrors research that has previously shown that feeding times can influence the phase of peripheral clocks in animals.”
Chilling hours signal to the bulbs that it is time to break dormancy and begin growing. This keeps the embryo from emerging during cold weather, which could lead to death of the new, tender growth.
The chilling hours for common bulbs grown in Louisiana are 12 to 16 weeks of temperatures around 35 to 45 degrees for tulips, snowdrops, hyacinths and narcissuses. Crocuses and daffodils require 15 to 16 weeks.
You can provide these chilling hours by storing bulbs in the refrigerator. Bulbs need darkness, consistent low temperatures of 35 to 45 degrees and moist soil or humid air, and your refrigerator is a perfect spot.
When chilling, keep bulbs away from fruits and vegetables that release ethylene gas (plant hormone) as part of their natural ripening process because it damages the embryonic flowers inside the bulbs.
If you chill them later, it means they will bloom later in spring. But, remember, bulbs native to colder climates do not tolerate our high temperatures, so starting late means you only have a small window before the heat is on in Louisiana.
If you have a specific question about something in the garden, reach out to your local AgCenter agents. You can locate information on each parish office at lsuagcenter.com.