Collecting and Preparing a Sycamore Seed for Planting

American Sycamore seed ball hanging from a tree in the fall.

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The American sycamore tree flowers in spring and completes seed maturity in the fall. Ending the maturation process as early as the first of September and continuing through November, the sycamore seeds ripen and are ready for collection and preparation for planting. The fruiting 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. Easier picking is after the fruiting head turns brown but waiting to just 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 to be collected in the Eastern forest. The California sycamore matures much earlier and should be collected during the fall season.

Collecting Sycamore Seed for Planting

Seed ball of an American Sycamore tree on the ground.

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

After collecting these fruiting bodies, the heads should be spread in single layers and dried 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 that are collected early in the season. Early ripening seed can have moisture contents as high as 70%.

Seeds from each head should be extracted by crushing the dried fruit heads and removing the dust and fine hairs that are attached to the individual achenes. You can easily do small batches by hand-rubbing through hardware cloth (2 to 4 wires/cm). When doing larger batches, it is advised to wear dust masks as the fine hairs that are dislodged during extraction and cleaning are a danger to respiratory systems.

Preparing and Storing Sycamore Seed for Planting

American Sycamore balls on a wood table against leaves.

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Seeds of all sycamore species do just fine in similar storage conditions and can be easily stored for long periods under cold, dry conditions. Tests with sycamore seed have shown that at moisture contents of from 5 to 10% and stored at temperatures of 32 to 45 °F, they are suitable for storage for up to 5 years.

American sycamore and naturalized London plane-trees have no dormancy requirements and pre-germination treatments are usually not required for adequate germination. Germination rates of California sycamore do 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, the dried seeds must be stored in moisture-proof containers, such as polyethylene bags. The rate of germination can be easily tested on wet paper or sand or even in shallow dishes of water at a temperature of around 80 F over 14 days.

Planting Sycamore Seed

Green Sycamore seedlings in the ground.

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Sycamores are naturally sown in the spring and you should mimic those conditions. Seeds should be placed in soil no deeper than 1/8 inch with each seed about 6 to 8 inches apart for proper spacing. Small, shallow starter trays with potting soil can be used to start the new trees and adequate soil moisture must be maintained and trays placed under indirect light.

Germination will take place over approximately 15 days and a 4" seedling will develop in less than 2 months under optimal conditions. These new seedlings then need to be carefully removed and transplanted from trays to small pots.

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