Kousa Dogwood is a tree in the Dogwood family, Cornaceae. It's native to Japan, but has been naturalized around the world due to its edible and ornamental value. They are quite hardy, and can be survive down to zone 5. The trees produce an abundance of fruits that taste sweet, juicy, and somewhat tropical. Their culinary use is largely unknown outside of Asia, and it's quite a shame as the fruits make delicious jams, sauces, and deserts. The Kousa fruits are larger than any other variety, so it takes little time and effort to gather a large supply. The trees are self fertile, so don't require another for pollination; however, they'll produce heavier yields if another dogwood tree is nearby.
The trees will naturally grow quite tall, but they respond very well to pruning, so can (and should) be cut to the desired shape and size. This variety typically starts to produce in its 3rd or 4th year. The soil should be made moist, but not damp. Sow the seeds 1/8 inch below the soil surface. Sprouts will emerge from the soil come next spring. Once germinated, and the first true leaf has formed, it's time to pot up to a larger container that contains a good quality potting soil if planted in a pot. If sown indoors, it is important to cold stratify the seeds for 12 weeks before sowing for best germination results.
Growing Dogwood seeds is actually quite simple. White Dogwood trees are actually native understory trees. After their showcase of large white flowers in the early Spring, the trees become somewhat normal looking. Along comes fall weather and the leaves start taking on a purplish tint. In nature, these seeds may take a few years to germinate, if at all. They are a favorite food for many birds and small wildlife. Here at the nursery, we try to grow these trees with as high a percentage as possible.
The seed pods are gathered as they start falling from the trees. The seeds are soaked in water. The fruit coating is removed by repeatedly rubbing until it is removed. The seeds are dried on a sheet of newspaper. Then they are kept in a plastic container with holes for ventilation. I have done Dogwood seeds 2 different ways and both have good success. One way involves looking at your last frost date in Spring and counting backward. The seeds need a cold period of about 120 days or so before they will grow. Counting back about that many days, start the cold treatment. The best way to do this is in the refrigerator. Seal them in a plastic bag of damp sand or potting soil. I prefer potting soil over sand. Take a fork, or something similar, and poke some breathing holes in the bag. After about 100 days, start checking the bags for rooting seeds. Once there are seeds with roots sprouting, they can be taken from the bag and sown in potting soil to grow on. Use your favorite method for this. The second way is almost like nature does it. We just up the percentages for success. The seeds have a very hard coating that prevents germination. The surface has to be compromised. The long cold period is one way. A long hot soak in water overnight is another. Some people nick the seeds with a small file to allow water inside. I like to take a small amount of my coarse sand, which is abrasive, and add it with my seeds. I then shake the seeds with this sand for several minutes. This causes lots of small abrasions or nicks. I then take this sandy mix of seeds and spread them out over the top of a large container of damp potting soil. Don’t worry about perfect spacing, remember nature? Once the seeds are spread out on the surface, I lightly cover them with a thin layer of additional soil. Roughly about a seed thickness on top. Last but not least by any means, cover the top with a piece of hardware cloth. Make sure the edges and corners are closed up well. Little critters just love that you have set out their favorite seeds for them. I like to use a small forked stick poked in the center to help support the hardware cloth. It keeps wet snow from flattening down on the top. Now just place on the ground in a protected area out of harm’s way. Once you see sprouting in the spring, remove the top. They can be grown in this container for a year or so. I remove any that are too crowded or growing deformed.
Seeds of the Chinese Dogwood have a deep dormancy within them, this requires a degree of patience to overcome and it is usually quite easy to get good levels of germination if the correct methods are followed. First pour warm water on to the seeds and leave to cool for around 24 hours. The water must not be too hot or boiling or the seeds will be killed. Next prepare a free draining substrate into which the seeds are to be mixed, this can be a 50/50 mixture of compost and sharp sand, or perlite, vermiculite. The chosen substrate needs to be moist (but not wet), if you can squeeze water out of it with your hand it is too wet and your seeds may drown and die. Mix the seeds into the substrate, making sure that their is enough volume of material to keep the seeds separated. Place the seed mixture into a clear plastic bag (freezer bags, especially zip-lock bags are very useful for this -provided a little gap is left in the seal for air exchange) If it is not a zip-lock type bag it needs to be loosely tied. Then write the date on the bag so that you know when the pretreatment was started. The seeds of this species require a cold period to break the dormancy that is within the seeds. This dormancy is their to prevent the seed from germinating during the autumn and winter when conditions outside would be unsuitable for growth. The breaking of this is easily achieved by placing the prepared bag of seeds in the fridge at 4 Celsius for a period of between 12 and 16 weeks. During this time make sure that the pretreatment medium does not dry out at any stage or it will be ineffective! It is quite possible for the seeds to germinate in the bag at these temperatures when they are ready to do so, if they do, just remove them from the bag and carefully plant them up. When the period of pre treatment has finished the seed should be ready to be planted. Small quantities can be sown in pots or seed trays filled with a good quality compost and cover them with a thin layer of compost no more than 1 cm deep. For larger quantities it is easiest to sow the seeds in a well prepared seedbed outdoors once the pretreatment has finished and wait for the seedlings to appear. It has also been found that fluctuating pretreatment temperatures that mimic the natural cycle can give the best germination results and I have myself had excellent results by keeping the mixed seeds in a cold shed through the winter for the cold stage of their pretreatment and allowing the temperature to fluctuate naturally. Ungerminated seeds can have the cold pretreatment process repeated again to enable more seeds to germinate. Do not expose newly sown seeds to high temperatures (above 25 Celsius). Keep the seedlings well watered and weed free. Growth in the first year is usually between 15 and 30 cm depending on the time of germination and cultural techniques and developing seedlings are usually trouble free.
Additional context and propagation notes
Flowering dogwoods (Cornus florida) are easy-going ornamentals if sited and planted properly. With their showy spring blossoms, these native plants are such a spring delight that nobody will blame you if you want a few more shrubs. Growing a dogwood tree from seed means propagation like Mother Nature does it. Read on for dogwood seed propagation information and tips for how to plant dogwood seeds. Dogwood Seed Propagation propagating dogwoods from seed couldn’t be easier. That’s why dogwoods grow so readily in the wild. The seeds fall to the ground and go about dogwood seed germination on their own. Your first step toward dogwood seed propagation is to collect seeds from native trees. To start growing a dogwood tree from seed, you’ll need to locate the seeds. Look for one seed inside each fleshy drupe. The seed is ready when the outer flesh of the drupe turns red. Don’t wait too long because the birds are after those drupes too.
When you are starting dogwood seed propagation, you’ll need to soak the seeds in water for a couple of days. All non-viable seeds will float to the top of the water and should be removed. Soaking makes it a snap to remove the external pulp, expediting dogwood seed germination. You can rub the pulp off by hand or, if necessary, by using a fine wire screen. As soon as the soaking and pulp removal is done, it is time to plant. Prepare a seedbed with well-draining soil, or a flat with well-draining medium. For best dogwood seed germination, plant each seed about one-half inch deep and 1 inch apart in rows 6 inches apart. Cover up the planted soil with light compost like pine straw to hold in moisture.
Starting Cornus kousa Dogwood from Seeds: Dogwood seeds can be started in the fall by soaking and removing the fleshy outer coating and sowing directly in pots to overwinter outdoors. This allows them time for the natural changing seasons and cold fluctuations - stratification. Cornus kousa is a dogwood that is native to Asia. due to its resistance to diseases like anthracnose which is brutal to our native dogwoods. In fact a number of cultivars are now on the market which are a cross between the native dogwood and the Kousa dogwood including one called Appalachian Spring which was introduced by the University of Tennessee. If you compare the drupes of the two types of dogwood you will notice some big differences. Size is the most obvious with the Cornus kousa dogwood reaching about 3/4 of an inch in diameter where the C. florida dogwood drupes are about 1/4 to 1/2 inch. Our native dogwood has drupes that are elongated where the Kousa is spherical. The native dogwoods bloom earlier than the Kousa dogwoods by several weeks. This gives the landscaper or gardener a nice option when planning spring flowering trees to ensure a succession of dogwood blooms.
Planting the Dogwood Seeds: When we got the drupes home I dropped them into a cup of water and let them soak. I didn’t keep track of how long I left them in the water but it wasn’t more than a week. Then I separated the seeds from the flesh of the fruit. Here is where I was very disappointed. Out of ten drupes only two had seeds. That’s the way it goes sometimes! The two seeds were already beginning to put out roots so rather than stratifying them in a moist bag of sand in the fridge I planted them directly into a pot. Dogwood seeds normally need a cold period to trigger germination so putting them in a cold refrigerator over the winter months is often a good idea. Dogwood seeds are great candidates to try winter sowing too. Assuming my two little dogwood seedlings spring up from the soil before cold weather hits I may have to bring them indoors to overwinter.
These notes illustrate that both Kousa and native dogwoods offer resilient options for gardeners, with multiple pathways to germination and cultivation depending on climate, available space, and desired scale of propagation.
