I have a Magnolia wilsonii in my garden, and this year there
is a definite profusion of seed that followed a long flowering season (I’m collecting more every day). What is the best way to sow and grow these?
According to the American Horticultural Society’s Plant Propagation,
edited by Alan Toogood (DK Publishing, 1999) you can collect fresh seeds
in the fall, and thoroughly clean them (the book recommends using a
fungicide to prevent rot or damping off). To extract the seeds, gather the
ripe cones and dry them until the fleshy fruits come away. Soak them in
warm water with liquid detergent for a couple of days to remove the outer
coating. Once softened, drain the water. Remove any flesh still attached,
and dry the seeds with tissue. Sow fresh and overwinter in a cold frame,
or mix with moist vermiculite, sand, or peat, and store in a plastic bag
in the refrigerator for 2 months before sowing. Seedlings may be
transplanted the following summer, and put back in the cold frame for a
second winter.
Another method is to stratify the seeds for 3-6 months at 41 degrees
Fahrenheit, sow under cover in spring with bottom heat (68 degrees) for
germination to take place in about a month. It will take plants grown
from seed from 3 to 10 years to flower, but some species take much
longer.
Texas A & M University’s horticulture department has an article on starting Magnolia from seed. The article focuses on Southern magnolia, but should still be relevant. Here is an excerpt:
“The seeds should be collected as soon as possible after the fruit is mature which is usually mid-September or early October. The cone-like fruit should be spread out to dry for several days until they open. The seeds can then be shaken from the dried cone or fruit.
“If the seed is to be kept for any length of time, the red pulp should be allowed to dry enough to lose its fleshy character, placed in sealed containers and stored at 32 to 41 degrees F. If stored over winter at room temperature seed will lose its viability. The seed should be cleaned before planting or stratifying. To remove the fleshy seed coat, soak the seed overnight in warm water. Remove the seed coat by rubbing against hardware cloth or window screening. After cleaning, the seeds should be sown immediately or stored for 3 to 6 months at about 40 degrees F and planted in the spring. An excellent way to stratify seeds is to use a polyethylene bag and place alternating layers of a moist medium such as a sand and peat mixture and seeds in the bag. Tie the top of the bag and place in a refrigerator at about 40 degrees. The medium should be just moist enough to stick together but not so wet that it will drip if squeezed by hand.
“Whether sown in the fall or stratified in the refrigerator and sown in the spring, the seeds should be covered with about l/4″ of soil and mulched to prevent drying. Seedbeds should be kept moist until germination is complete. Partial shade should be provided the first summer for seedlings.”