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Winter Sowing Tree and Shrub Seeds

High Caliper Growing, January 22, 2016

Winter sowing is a technique used to propagate certain trees and shrubs, as well as some annuals, perennials, and vegetables. It involves sowing seeds of these plants outdoors in the autumn or winter, instead of in the spring – much like Mother Nature would if the seeds were left to drop naturally.

Many shrub and tree seeds require a period of cold to break dormancy and germinate. Known as stratification, this period of cold is often artificially induced by placing the seeds in a freezer or refrigerator before planting them, but when seeds are winter sown in colder climates, the appropriate stratification period happens naturally.

The benefits of winter sowing are many.

  • First, growers can save money on expensive seed-starting equipment when they winter sow seeds. There’s no need for grow lights, germination chambers, or other special gear when starting seeds. All that’s needed are a few containers filled with a well-draining, peat- or coir-based potting soil blended 50/50 with compost. Fabric Root Control Bags make great winter sowing containers.
  • Winter sowing doesn’t take up much space. Several seeds can be planted in each pot, and the pots can be tucked into a shady corner of the yard or garden. Containers are best left on the ground, so there’s not even a need for tables or cold frames to store them.
  • The best time to winter sow seeds is when the growing season is over; there’s no need to fit seed starting into your already-busy spring schedule.
  • There’s also no need to harden-off seedlings grown via winter sowing. They’ll already be growing outside, so no special accommodations will have to be made before moving the plants outdoors.
  • Winter sown seeds will germinate and grow at the appropriate time for their species. There’s no need to guess or count calendar days to encourage the proper germination of plants – in most cases, they’ll do it just fine on their own.

What trees and shrubs respond best to winter sowing?

The seeds of tropical plants, tender annuals, and frost-sensitive species are not good candidates for winter sowing, but many cold-hardy trees and shrubs are. Look first to native species that grow well from seed; these are almost always good candidates for winter sowing. Seeds collected from a hybrid trees or shrubs may not result in a plant that’s identical to the parent. For the best results, winter sow seeds of straight species, instead of hybrids.

A few trees and shrubs that perform well when winter sown include:

  • Oaks
  • Maples
  • Crepe myrtle
  • Nut trees, such as hazelnuts, hickories, walnuts, etc.
  • Holly
  • Beech
  • Ash
  • Horse chestnut
  • Red bud
  • Tulip poplars
  • Viburnum
  • Elderberry
  • Euonymus
  • Serviceberry
  • Elm
  • Birch
  • Chokecherry
  • Honey locust
  • Lilac

Learn how to winter sow.

To winter sow, simply bury several tree seeds or shrub seeds of the same variety in a Root Control Bag filled with the potting soil/compost blend. Typically, a depth of one-and-a-half-times the height of the seed itself is best. Space the seeds a few inches apart, and label the container so you know what’s planted in it. Water the seeds in, and put the pot in a sheltered site, if possible.

If you start seeds of perennials, annuals, or other non-woody plants via winter sowing, you’ll also need to cover the tops of the container with a cloche of some type for added protection. A layer of clear plastic will suffice. Shrub and tree seeds do not typically need this extra insulation, though tossing a handful of straw or shredded leaves on top of the pot helps insulate the seeds.

Come spring, the germination of plants will take place when the seeds are ready. The seedlings can then be separated and re-potted, or planted in the ground as soon as they reach a few inches in height.

 

Potential problems with winter sowing.

Occasionally rodents or birds may dig up your seeds during the winter. To keep this from happening, pots can be topped with a layer of protective hardware cloth. Just be sure to remove it in the spring, before the seeds germinate and grow up through it.

If natural precipitation doesn’t occur, you’ll have to irrigate your pots occasionally throughout the winter, but don’t keep them overly wet or the seeds may rot.

Winter sowing is a great way to propagate trees and shrubs. It’s smart, simple, and fun!