Are your fingers itching to do a bit of gardening? This is the slow time of year when we find ourselves thumbing through gardening books and catalogs with our warm beverage of choice. But winter’s freezing temperatures, when so much of our garden sleeps, provides the cold required by many woody seeds to germinate.
Winter is a good time to work with woody seeds. While it remains too early for most of us to start herbaceous seeds for flowers or spring vegetables, we can sow many interesting seeds for trees and shrubs.
Some seeds, like most oaks, require several months of cold before their seed coats will break open and allow the embryo plant to emerge. There is a good reason for this insurance against early germination. The plant’s rhythms allow for the maximum number of newly germinated seeds to begin growth when conditions are favorable. The baby plants must be able to survive their first winter.
Other seeds, from trees native to warmer climates, don’t require this period of cold. In fact, they require consistent warmth to trigger growth. Date palms, citrus trees, avocado trees and even most apples and pears will germinate after a few weeks of moist warmth. You may have found a germinating seed in a grapefruit or orange from time to time as you were eating the fruit. If you are careful with the embryo, you can plant that little seed and watch it grow.
Seeds wanting warmth may be started indoors, maybe even in a kitchen cabinet or on the counter. Seeds requiring cold stratification should be left outdoors in a location protected from hungry squirrels, or kept in a refrigerator.
There are several ways to coax a seed to germination. But my favorite way involves nothing more technical than damp paper towels and a zip lock baggie. The towel should be moist, but not drippy wet. One or more seeds, depending on their size, may be rolled up in the towel, the towel folded and sealed in the bag, and the bag put in a safe place to wait for the seeds to awaken.
I saved some citrus seeds while making cranberry relish in the days before Christmas. They are just beginning to germinate, after only a few weeks in a kitchen cupboard.
As soon as the embryo plant emerges, the seed may be planted into a pot of loose soil mix. Add pine bark, sand, perlite, poultry grit or aquarium gravel to standard potting soil. You might also mix in some finished compost to feed the young tree. Tree roots need some air pockets to breathe, and may rot in compacted, saturated potting soil. Plant the seed near the surface, green stem emerging from the soil if it is more than an inch or so long.
Finish the pot with a light mulch of aquarium gravel or vermiculite to discourage damping off disease. Vermiculite is sterile, and can help prevent this common fungal problem. Some growers might sprinkle cinnamon powder on the soil too, as cinnamon is an anti-fungal and can help prevent ‘damping off disease.’
Hardwood tree seeds that I wrapped in paper towels in the fall can germinate at any time. Keep watch over those seeds by checking every few weeks for growth. If there is any sign of mold or sliminess on the towel or seeds, carefully wash the seed and wrap it in a clean towel. You may need to do this a time or two before the seed germinates, depending on the seeds and the temperature where it is stored. Once the embryo appears, move them out of the towels and into a pot of soil.
I found some Camellia sasanqua seeds, harvested in November, germinating a few weeks ago and moved them to pots of soil. As their stems and first leaves emerge, I’m moving those pots into brighter light to encourage growth. Other seeds from that batch are just cracking open now with the first hint of new growth.
Starting hardwood seeds requires patience and commitment. If you try to collect seeds from your favorite holly shrub, after cleaning them and stratifying them, you might wait for as long as two years for the woody covering over their embryo to crack and allow new growth.
Some seeds found in drupes, like holly seeds, germinate better after an acid bath. That might happen in the digestive system of a bird or in a solution made by a dedicated gardener.
Seeds must be kept moist and protected until they begin to grow. Some seeds want a period of warmth, then a period of cold, and then require warmth (spring) again before the embryo emerges from the seed. These seeds might be kept at room temperature for a while, then kept in a refrigerator drawer, or outdoors for 60—90 days, and then returned to room temperature to germinate. It is smart to learn about the particular needs of each type of seed you plan to grow.
Seeds from trees native to our climate might or might not require a period of cold stratification. Oak seeds that I collected in September had begun to germinate by late October. I planted those with emerging embryos into pots of soil, and those pots are outside, waiting for further growth in the spring.
Even after sowing a germinated seed in a pot, it still must be kept moist but not too wet, and at its preferred temperature for some period of time before it begins to grow into a new plant. I’m keeping my potted oak and red buckeye seeds in shallow plastic storage boxes, loosely covered with their lids, and checking on them every few weeks. I have several dozen oak seedlings potted, and another dozen or so oak seeds still in cold stratification.
These seedling trees will be offered up through local plant sales in late spring. With that in mind, I’ve recently been digging and potting seedling trees that germinated in areas where they can’t be allowed to grow to maturity. If you have a mulched area in your yard, you might notice all sorts of little seedlings emerge. Some grow from seeds that fell years ago, waiting for the ‘right’ conditions to grow. I especially appreciate finding holly seedlings germinated in the wild.
I have nearly 20 Virginia pine seedlings and another 20 holly seedlings potted and growing on. It is sometimes difficult to identify seedlings found in the wild because their early leaves may differ from the mature leaves of their species. I won’t be sure of these holly trees until they mature a bit, though at least some may have a Foster holly growing nearby as their female parent. When several different species and hybrids of the same genus grow near one another, the seedlings may well be a new, unnamed hybrid.
The same will probably be true of seeds saved from citrus, apples, pears, avocados, or other fruits. The seedling may grow into a tree unlike the parent. Once mature, its fruit may be different than the fruit the seed was harvested from originally. So many crop-producing trees grown commercially are already hybrids or sports, the seeds they produce may be something different and new.
But if you are a gardener with fingers itching to garden in January, working with woody seeds proves a happy diversion. So, look around and see what you can collect, what you have on hand or can buy at your local grocery store. Grab a damp paper towel, a zip-lock, and ‘plant’ something fun.