When Plants Go to Seed
Observing plant adaptation in the garden
Longing is like the Seed
That wrestles in the Ground,
Believing if it intercede
It shall at length be found.
The hour, and the Clime—
Each Circumstance unknown,
What Constancy must be achieved
Before it see the Sun!
-Emily Dickinson (1873)
In midsummer, as many plants approach full stride and others cross their finish line, we may find ourselves gingerly pulling up declining specimens to make way for late season crops. But as we do so, let’s take a moment to appreciate the exponential growth of all these tiny seeds we tucked into the earth earlier this year, and how they allocated a great deal of their energy toward fruit production. As you work in your garden, pause to examine how your plants have evolved various strategies to best disperse their seed. You’ll find a delightful variety of fruit forms among different species, and it’s fun to guess why a plant may have evolved one type of fruit versus another for the purposes of seed dispersal.
Botanists use three basic criteria for classifying different types of fruit: simple fruit (such as tomatoes, grapes, and nectarines) form from a flower with a single ovary; aggregate fruit (such as raspberries and mulberries) form from a flower with multiple ovaries; and multiple fruits (such as pineapple) form a single, edible mass but are really several fruits formed by multiple flowers with single ovaries. All three fruit types protect seeds as they mature and then disperse them away from the parent plant once maturity is reached.
To be sure, this final stage of reproduction looks different depending on the species. Have you ever shaken a dried poppy capsule like a baby's rattle? Aside from the lovely cymbal-shiver sound it makes, you may have noticed some tiny, perfectly round, black seeds spill from the miniature “turret” on top. Poppies, it seems, best disperse their lightweight seeds when rattled by the wind.
Similarly, the tiny seeds of chamomile are easily carried off by a soft breeze. Examine a dandelion, salsify, or milkweed seed and you’ll see that they come with their very own “parachutes” to travel great distances on the wind.
Wind, water, ballistics, animals, and gravity are all means by which plants disperse their seeds. Bristly burr seeds are built for hitching rides on animal fur; other hard-coated seeds (such as melons) use a fleshy and delicious pericarp to entice animal digestion as a “pre-treatment” to germination. Seeds from plants like wood sorrel and touch-me-not use ballistic mechanisms to shoot seed several feet away; whereas arugula, peas, beans, and spider flower form carpels or siliques that dry and then shatter to sprinkle seeds nearby. Coconuts are large seeds with air-filled chambers and water-resistant husks that allow them to float great distances on ocean currents. Borage seeds, on the other hand are dense relative to their size, and need only gravity to tumble to the ground and roll away.
For millennia, plants have also used humans to disperse their seed: through agriculture as well as through trade and migration routes. And our long relationship with plants has taught us various techniques for saving, storing, and germinating seeds. Touring our garden can be a most humbling experience when we consider the resilience and inventiveness underlying plant adaptations: even as gardeners, we are merely supporting cast in the story of seed survival and dispersal.
Of course, many plant species introduced to the specific conditions of our garden and climate really do need our help to propagate. And by pausing to examine the morphological strategies employed by our plants, we can gain insight about the growing conditions which best suit them. Are the seeds so tiny and delicate that they would likely be carried by wind and easily germinate on the surface of soil? Or, are they covered in a hard seed coat built to withstand long periods of moisture underground? Are they the kind of seeds that do best after they've been partially digested by an animal? Many effective seed-saving and seed-sowing methods were derived from looking closely at plants to see what they do to survive.
If you would like to learn more about seed-saving techniques, we invite you to revisit this curated list of seed-saving guides--for both the beginner and intermediate seed-saver--or simply use the search bar on our blog page to discover more great gardening topics.