Growing a Sweet Gum Tree

Question:

Today I took some sweet gum balls from a tree that my late father had planted some 40-50 years ago. I thought it would be neat to have a tree that was a direct descendant of a tree planted by him. The gum balls are green. Can you tell me what I need to do to produce a sweet gum tree including getting the seeds from the gum ball to when and where to plant? Thanks so much!

Hardiness Zone: 6a

G. Brent from St. Louis, MO

Answer:

Brent,

In my opinion, planting trees is one of the few ways to create lasting positive change in the world. When you pause to consider how significant a tree is, you realize that just one tree offers food and refuge to hundreds of insects, animals and birds; offers beauty, shade and clean air to human beings; and gives the entire planet another carbon sink. It does all this for 100's of years, and that doesn't even include the tree's potential offspring! I think this is a great idea-and a wonderful way to honor your father.

Sweet Gum Trees make beautiful shade trees. You can propagate them from seeds or cuttings. Starting seeds will take a lot longer, but since you've already collected the gumballs, let's start there. Later, if you can't get the gumballs to germinate, try starting a new tree using a cutting and a little rooting hormone. It will take 60-100 days to root, but once it gets going, these trees grow fairly fast.

Gumballs turn brown with age. As they turn color on the tree, the heads pop open to disperse the seed. The gumballs can be taken from the tree safely for a few weeks before they turn color without hurting the seed. If the gumballs you collected are green, you can continue to let them dry and pop open, or try to gently pry them open yourself to access the seeds. Inside each prickly point are 1 or 2 winged seeds (usually dispersed by the wind). The entire gumball can contain as many as 50 seeds in a good year, and as few as 5 in a bad year (it runs in 3-year cycles). The amount of seeds found in the gumballs tends to correlate with how viable they are. The more seeds the ball has, the more likely it is that those seeds are of good quality.

I'm no authority on Sweet Gum Trees, but my understanding is that the seeds need to be cold treated in order to get them to germinate (approximately 12 weeks at 40F).

Steps in cold stratification are:

1. Soak the seeds overnight or from 12 to 24 hours in water.
2. Place the seeds in a plastic bag, tray or pot filled with a moistened soil-less mix of some kind. This can include sand, peat moss, etc. Whatever medium you choose, it will need to stay moist.
3. Place the seeds in your refrigerator (37-40°F) for 3 months and check on them occasionally to make sure the medium is still moist.
4. After 3 months, plant the seeds immediately before they return to a dormant state. You may want to start them in pots indoors to avoid losing them to animals and birds.
5. Move the seeds to a pot for germination. Generally, seeds should not be planted deeper than 1 to 2 times their diameter. Moisten the medium before sowing seeds. After sowing the seeds, water with a fine mist to avoid disturbing the soil and covering the seeds. Try to keep both the soil and the air humid throughout the germination process. If you prefer, cover the pot with plastic or the top half of a 2-liter bottle (cap on) to keep it moist.
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6. Place the seeds in a location that receives bright light. Direct sunlight should be avoided.
7. Be patient, the seeds of trees and shrubs sometimes take FOREVER to germinate.
8. Transplant seedlings into larger containers as soon as the first 2 to 4 true leaves appear (not the cotyledonary leaves). Retain as much of the medium around the roots as possible while transplanting to minimize shock. Before transplanting outdoors (full sun), take time to harden off seedlings and gradually adjust them to outdoor conditions.

Good Luck!
Ellen