Collecting, Preparing, and Planting Sycamore Seeds

The American sycamore tree flowers in spring and completes seed maturity in fall. Ending the maturation process as early as the first of September and continuing through November, sycamore seeds then ripen and are ready for collection and preparation for planting. The head is persistent and will delay seed drop out of the fruiting "ball" until January through April.

The best time to collect the fruiting balls or heads, usually directly off the tree, is just before they begin to break up and the hairy-tufted seeds start falling. It's easier to pick the fruiting heads after they turn brown but also after leaf fall. Because these seed heads are persistent on limbs, collections can be made into the next spring and usually make sycamore the last fall-maturing species collected in the Eastern forest. The California sycamore matures much earlier, so you should collect its seeds during fall.

Collecting Sycamore Seed for Planting

Picking fruit heads by hand is the most common collection method. At the northern and western limits of the sycamore range, intact heads can sometimes be found and collected off the ground late in the season.

After collecting these fruiting bodies, spread the heads in single layers and dry them in well-ventilated trays until they can be broken apart. These heads can look dry on collection but layering and venting are essential, especially with fruit heads collected early in the season. Early ripening seeds can have a moisture content as high as 70%.

You should extract the seeds from each head by crushing the dried fruit balls and removing the dust and fine hairs attached to the individual achenes. It's easy to do small batches by hand-rubbing the balls through hardware cloth (2 to 4 wires/cm). When doing larger batches, wear dust masks because the fine hairs dislodged during extraction and cleaning are a respiratory danger.

Preparing and Storing Sycamore Seed for Planting

Seeds of all sycamore species do fine stored for long periods under cold, dry conditions. Tests with sycamore seeds have shown that they're suitable to store for up to five years at moisture contents of 5 to 10% and stored at temperatures of 32 to 45 °F.

American sycamore and naturalized London plane trees have no dormancy requirements and pre-germination treatments usually aren't required for adequate germination. Germination rates of California sycamores increase from moist stratification storage for 60 to 90 days at 40 F in sand, peat, or sandy loam.

To maintain low seed moisture under moist storage conditions, you must store the dried seeds in moisture-proof containers, such as polyethylene bags. You can easily test the germination rate on wet paper or sand, or in shallow dishes of water at a temperature of around 80 F over 14 days.

Planting Sycamore Seed

Sycamores are naturally sown in the spring and you should mimic those conditions. Place seeds in soil no deeper than 1/8 inch with each seed about six to eight inches apart for proper spacing. You can use small, shallow starter trays with potting soil to start the new trees, and you must maintain adequate soil moisture and place trays under indirect light.

Germination will take place over approximately 15 days and a four-inch seedling will develop in less than two months under optimal conditions. You must carefully remove these seedlings and transplant them from trays to small pots.

Tree nurseries in the United States typically outplant these seedlings one year from germination as bare-root seedlings. Potted trees can go several years before re-potting or planting in the landscape.