How to Start Tree and Shrub Seeds in the Fall (Seed Prep)

Fall is the perfect time to start preparing tree and shrub seeds that need a period of cold weather before they’ll sprout. When seed starting tree and shrub seeds I use two techniques that help to trigger better germination rates. The first technique is simply soaking the seeds. The second process is called stratification and mimics the natural cycle seeds experience outdoors. The pre-soak helps to remove pulp and growth inhibitors to get things started. I’ll walk through a few examples from the garden that I just got started including: Japanese maple, dogwood, sweet gum, and American beautyberry. Each one has its own quirks, but they all share the same basic principle: patience pays off.

I’ve included a video below with a demonstration of everything in this post.

Japanese Maple Seeds (Acer palmatum)

Japanese maple seeds, or samaras, come with natural growth inhibitors (mainly tannins) that slow down germination. The first step is a simple soak. Place the seeds in water for 24 to 48 hours. You’ll notice the water darkening as those inhibitors leach out, which shows the process is working. You can remove the samaras as they aren’t necessary but it takes extra time to do so. It’s an optional thing but can make sowing a little easier.

Once soaked, the seeds are ready for outdoor overwintering. Surface-sow them in a pot, cover them with soil (enough to cover the entire seed), and protect the pot with a breathable row cover cloth. The cover keeps birds accessing the seeds while still allowing air and moisture to pass through. If you have rodents in the area you may want to add a cover of hardward cloth to help prevent them from partaking of your seeds for dinner! Over winter, nature handles the cold stratification for you, and by spring, you’ll have a shot at those tiny maple seedlings breaking through.

Dogwood Seeds (Cornus florida)

Dogwood seeds are tucked inside a pulpy red berry that you’ll need to clean first. The pulp contains compounds that prevent germination (inhibitors), so removing it is important. A brief soak in a glass of water for about a day helps soften the berry flesh up, but often you can just squeeze the seeds out by hand. More on Dogwood Seeds

This step also gives you a chance to check for pests since maggots sometimes make themselves at home inside the fruit. Unfortunatelt that was a find in my latest batch of dogwood seeds. If that happens, a mild dish soap soak helps clean the seeds. You don’t want to do this for very long, maybe an hour or so, then soak again in clean water. Once the seeds are free of pulp and debris, plant them in a container, cover lightly with soil, and set them outside for their natural cold stratification cycle.

Magnolia Seeds can be treated the same way as dogwood seeds. Here’s more info on Starting Magnolias from Seed.

Sweet Gum (Liquidambar styraciflua)

Sweet gum seeds come from those unmistakable spiky “gumballs.” I know a lot of people don’t like these trees becauase of “nature’s caltrops” but they have a ton of wildlife value! Sweetgum tree seed are very straightforward to collect and don’t need soaking. For collecting gather the spiked seed balls when fully formed and still green. Put them in a paper back and let them dry out. In a few days the seeds will be expelled from the seed ball and are very easy to collect. You will also get a large about of chaff from the seed ball which you can discard. The seed itself resembles a tiny maple tree samara.

Sprinkle the seeds onto the soil surface, cover with a thin layer of soil, and water them in. It may help to water the pot prior to planting to make sure you the soil is completely watered. While sweet gums can be messy trees, the narrow ‘Slender Silhouette’ variety offers a tidier, space-saving option for landscapes. That’s where my recent batch of seeds came from. ‘Slender Silhoutte’ is a variety that grows very tall but stays narrow. It’s great for adding a dramatic verticle element to your garden design!

Liquidambar styraciflua ‘Slender Silhouette’

American Beautyberry Seeds (Callicarpa americana)

American beautyberry seeds, on the other hand, are tucked inside bright purple berries. Those berries need a soak to loosen and remove the pulp before planting. Once cleaned, plant the seeds in pots, cover them lightly, and protect them with a row cover just like the others. Both species benefit from a natural winter outdoors, letting the cold temperatures and moisture do their work. In the spring if all goes well the beautyberry seeds will germinate. They can be transplanted into a larger pots once they have a few true leaves.

Understanding Cold Stratification

Cold stratification is nature’s timing mechanism. In the wild, it prevents seeds from sprouting too early, ensuring they wait until spring warmth returns. By exposing seeds to a period of cold and moisture, we can help break that dormancy and trigger germination.

There are two main ways to stratify seeds.

Natural Stratification:

Sow seeds outdoors in fall and let winter handle the rest. This is what I’ve described above. In my opionion it is the easiest method as you are allow the seasonal weather patterns to influence the seed’s germination. We speed it along a little bit with the pre-treatment of the seeds but otherwise is left to naturally function.

Simulated Stratification:

For more control, you can place seeds in a damp medium such as peat moss inside a sealed container and refrigerate for several weeks or months, depending on the species. I’ve actually used a paper towel with Japanese maple seeds before and achieved a good germination. The opening and closing of the fridge actually allowed the seed to germinate while still in the bag! (Japanese maple seed germination)

An Extra Thought

There are a number of seeds that can be stored and stratified while dry. I’ve had good success simply storing the dry seeds in the refrigerator. It seems to satisfy their cold needs and improve germination later.

Patience is very important. Some tree seeds need more than one chilling period, or even two full winters, before they wake up. But once they do, that first bit of green feels very well-earned. Don’t forget to check out the video above for more details on these processes!