In the Garden:
Here's a garden just waiting for the right conditions for it to explode with lush growth.
Good Things Come in Small Packages
It's a new year, the days are getting longer, and seed catalogs have arrived, brimming with tantalizing photos of new varieties to try. Life is good. Over the years I've started thousands of seeds indoors, yet I'm always awed by the process. How can a tiny, inert, rock-hard nugget be so quickly transformed into a lush green plant, exploding with life? The biology of seeds isn't just fascinating, however, it is also important for gardeners who start their own seeds.
Are Seeds Alive?
Teachers may sometimes spark classroom debate by asking students, "Are seeds alive?" Even adults, however, have trouble answering this question. Scientists avoid having to give a yes-or-no answer by providing a third alternative: Seeds are neither alive nor dead; they're dormant. Although they show no signs of metabolic activity -- a commonly used indicator of the presence of "life" -- viable seeds contain everything they need to burst forth and grow. But until they are exposed to the proper environmental conditions, they remain in a state of rest.
If you think about the role of seeds in nature, that packet of seeds holds even more wonderment. Seeds not only carry the genetic information for a plant species, they enable the species to endure harsh conditions that render growth impossible. Depending upon the plant's native habitat (the environment in which it evolved), these unfavorable conditions might be extreme cold or heat or drought.
Here in the Northeast, plants face long, cold winters. Some, like deciduous trees and shrubs, enter a phase of dormancy. Evergreens don't go dormant, but they slow their metabolism dramatically. Herbaceous perennials die back to the ground, letting just their roots overwinter. And most of these plants also set seeds -- seeds that generally sit dormant over the winter, but will sprout to life in the spring. How do seeds in temperate regions like ours "know" not to germinate during a warm spell in autumn?
Giving Seeds the Deep Chill
Seeds from many temperate plants evolved the survival mechanism of requiring an extended period of chilling before they will germinate. This ensures that they won't germinate and begin growth, only to be killed by the cold. If you have ever tried to start seeds of lavender, primula, or delphinium, you probably know about prechilling, or "stratifying," seeds. To get these seeds to germinate, you must mimic the conditions they would face outdoors; that is, you must expose them to moist, cool conditions for an extended period. A good way to accomplish this is to sow the seeds in moist seed-starting mix, place the flat in a plastic bag, and then store the bag in the refrigerator for the specified length of time.
Overcoming Tough Seed Coats
Some seeds have especially tough seed coats, making them impervious to water and therefore slow to germinate. Why might seeds have evolved this feature?
Consider that most seeds grow best when buried in soil, as opposed to simply lying on top of the soil. The delicate roots and emerging shoots are much less likely to dry out if they are covered with soil rather than baking in the sun on the soil surface. These plants have the best chance of surviving and reproducing if they have hard seed coats that require either the grinding action of soil particles to pierce the seed coats and allow water uptake, or exposure to soil fungi and bacteria that decompose the seed coats. Thus, nature has devised ways to keep certain types of seeds from germinating until they are "planted."
Some plants have seed coats containing germination-inhibiting chemicals that must be washed off with copious amounts of water before the seeds will germinate. Other seeds have evolved to germinate most readily after exposure to the acidic environment of a bird's gut, thus insuring the species will be spread far and wide. These seeds are often surrounded by tasty, fleshy fruits; birds eat the fruits and pass the seeds, along with a dose of fertilizer!
Gardeners deal with the tough seed coats of morning glory and sweet pea seeds by soaking or scarifying. Soaking means placing seeds in warm water for a prescribed length of time. Scarifying means making a hole in the seed coat by nicking each seed with a file or nail clippers so it can absorb water. To scarify larger quantities of seeds, line a can with a coarse grade of sandpaper, then place the seeds in it and shake until the seeds are scratched.
Let There Be Light
Why do some seeds need light to germinate? Once again, nature gives us clues. Consider a seed that's fallen in a dense grove of trees. Would it have much chance to grow and compete in that environment, with little light and competition for water from all those tree roots? Now, consider the same seed, planted in an open field where it receives plenty of light and water. Maybe the seed was carried there by a bird or animal. Or perhaps a windstorm knocked down a tree in the grove, opening up a patch of ground to the sunlight. That little seed has a fighting chance to grow. If you are sowing seeds that require light to germinate, simply press them into the soil surface, and leave the seed tray exposed to light.
Trial by Fire
Finally, some seeds, such as those of chaparral-type plants growing in regions exposed to frequent lightning storms, require exposure to fire in order to germinate. When the competition from other vegetation is reduced by fire, these seeds have a fighting chance. Fortunately, I don't know of any common garden plant that requires gardeners to go to this extreme!
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