Due to the large number of maple tree species that grow in nature, there is no single germination method that works for all of them. Some maple species are easy to grow, especially those that sow seeds in the spring or early summer, but others are so difficult to grow that professional foresters can only get a germination percentage of 20-50%. If possible, find out what maple species you have before you start. If not, then try using the cold stratification method.
Step
Method 1 of 3: Cold Stratification
Step 1. This method can be tried for most maple seeds
Sugar maples, broadleaf maples, boxelder maples, Japanese maples, Norwegian maples, and some red maples will become dormant in winter and germinate as soon as temperatures warm. The cold stratification method can produce very high germination rates for these species.
- All of these maple species sow their seeds in the fall or early winter. If your maple tree drops seeds in spring or early summer, use the soil germination method.
- If you are planting the seeds outdoors, start this method about 90-120 days before the last winter frost.
Step 2. Fill a plastic bag with growing medium
Place a handful of peat, vermiculite, or germination paper in a small, resealable plastic bag. For best results, use sterile materials and insert with gloves on to avoid fungal infections.
- Use a plastic bag the size of a snack pack. If the plastic bag is too large, more air will be trapped along with the seeds, which can lead to mold growth.
- Red maple seeds are usually sensitive to acids. For this species, use neutral or alkaline vermiculite instead of acidic peat.
Step 3. Add a little water
Put a few drops of water on the growing medium to slightly moisten the material. If you can see water droplets in it, or if you can squeeze the material until the water comes out, it means your growing medium is too wet.
Step 4. Add a small amount of fungicide (optional)
Fungicides can prevent fungal attack on your seeds, but they are not always necessary, and too much can damage the plant. Give in small quantities, according to the manufacturer's instructions.
Instead of applying a fungicide, some people prefer to wash the seeds in a very dilute solution of bleach
Step 5. Put the seeds in the bag, then close it
Put about 20 to 30 seeds in each plastic bag. Roll up the bag from the bottom to remove most of the air inside. Then, close the bag.
Step 6. Store your seeds in the refrigerator
Now it's time to "stratify" your seeds, by exposing them to temperatures that will promote germination. For most species, the ideal temperature required is usually between 1–5ºC. Usually, this temperature can be reached on the 'crisper' rack in the refrigerator.
- We recommend using a thermometer to confirm the correct temperature. Some seeds will not be able to germinate if the temperature is not right even by a few degrees.
- Wherever possible, store boxelder and Norwegian maple seeds at a temperature of exactly 5ºC, and red maple seeds at exactly 3ºC. The other species are not as sensitive as the three species.
Step 7. Leave for 40–120 days, check once every one or two weeks
Most of these species take between 90 and 120 days to germinate. However, broadleaf maple and some other species can germinate in as little as 40 days. Every week or two, check your plastic bag and adjust its condition if needed:
- If you notice condensation, lift up your plastic bag and tap gently to drop the water droplets. Lay the bag on the reverse side so the wet seeds can dry.
- When the growth medium dries up, add a drop or two of water.
- If you notice mold or black spots on a seed, remove the seed and throw it away. (If all the seeds in the bag are infected with fungus, add a little fungicide.)
- When your seeds start to germinate, remove them from the refrigerator.
Step 8. Plant your seeds
Once the seeds begin to germinate, plant them in moist soil to a depth of 0.6–1.2 cm. Most maple trees do well in shaded areas, but it's a good idea to find out your exact type of maple for more information on how to grow it.
To increase the survival rate, sow your seeds in trays in the room. Fill your tray with 7–6–10 cm deep seed growing medium with good drainage, or try using a mixture of peat, compost, vermiculite, and grits. Water your nursery medium when it is completely dry. Transfer the seeds to the pot as soon as the second wave of leaves begins to appear
Method 2 of 3: Warm and Cold Stratification
Step 1. Use this method for mountain and Asian maple species
Species such as grape maple, striped maple, Amur maple, and paperbark maple are difficult to germinate and require more attention. The same is true for most other maple species native to Asia, as well as for mountain and rocky mountain maples.
All seeds that fall under this category are sown in the fall or winter. If left alone in the soil, the seeds will take years to germinate
Step 2. Scrape off the seed shell
There are many species of maple that have a very hard shell (pericarp). Growers often “scrape” the shells to increase the germination percentage. You can do this by one of the following methods:
- Scrape the base of the seed (opposite side of the seed wing) against the nail head or sandpaper. Stop once you've cracked a bit of the shell so you can see the surface of the seed inside.
- Soak your seeds in homemade hydrogen peroxide for a few hours, then rinse well.
- Soak your seeds in warm water for 24 hours.
Step 3. Store your seeds in a warm room
The United States Forest Service recommends storing your seeds at 20–30ºC for 30–60 days. Unfortunately, these seeds have not been studied as thoroughly as the seeds of other species, so species-specific guidelines are not yet available.
Step 4. Cold stratification for 90–180 days
Transfer your seeds to a resealable plastic bag filled with peat or other planting medium, then place them in the refrigerator. Check every two weeks, watching for signs of mildew, drying, or germination. Rocky mountain maple (Acer glabrum) seeds will usually take a full 180 days to germinate. Other species can take as little as 90 days, although in reality it is difficult to predict.
- For more information, see the cold stratification method above.
- Do not expect germination of all existing seeds. A low germination percentage-only 20%-is common in the above species.
Step 5. Plant the seeds
You can start germinating your seeds in nursery trays indoors or outdoors when the last frost has passed. Plant at a depth of 0.6 to 2.5 cm below the soil surface. Water occasionally well, don't let the soil sit too dry for too long.
For more specific information, look up the specific name of your maple species
Method 3 of 3: Germination in Soil
Step 1. Collect your seeds in late spring or early summer
Silver maple and some species of red maple (with the exception of the Japanese red maple) will sow seeds early in the growing season. These species do not have a dormant period, and do not require special treatment.
Some red maple trees will not sow seeds until fall or winter arrives; therefore, the species will require cold stratification. Not only that, trees that sow their seeds early in the season can experience both good and bad years of seed production
Step 2. Plant the seeds immediately
Seeds of this type will die when dry in storage. Plant as soon as you collect them. The seeds will germinate quickly.
Step 3. Plant in moist soil
Place the seeds in moist soil with a variety of organic matter and other debris on the surface. As long as the soil doesn't dry out, the seeds won't need additional care.
Step 4. Plant in a sunny or slightly shaded area
Silver maple is difficult to grow in fully shaded areas. Red maples can grow in the shadows for 3–5 years, but if they are kept under the canopy throughout this period, this type of maple will also have difficulty growing.
Step 5. Do not disturb your nursery (optional)
If some seeds fail to germinate, often new sprouts will appear the following year. These seeds are usually in the minority, but if your germination percentage is low, you should not disturb the planting area during the second season.
If the percentage of seed germination is very low and the climate is not problematic, the seeds are likely to have died during storage. Plant the next seeds next year, don't wait
Tips
- If your Japanese maple seeds dry out in storage, soak them in 40–50ºC water, then allow the water to cool slowly for 1–2 days. Remove from water and apply cold stratification as described above.
- Maple boxelder (Acer negundo) is a more difficult species to germinate than other cold stratified species. If the seeds are dry and very hard, break the outer shell first before you start.
- If the stratification process is deemed too draining of your resources, you can sow the seeds directly in the ground in late fall. The species mentioned in the cold stratification method may germinate in the spring, but many of the seeds will remain dormant. The species mentioned in the warm and cold stratification method usually take years to germinate. If you don't want to wait, scrape the underside of the fruit wall (the opposite side of the seed wing) and the underside of the seed coat as well. Don't expect a success rate of more than 20–30% if you start to notice seeds that germinate.
