The cottonwood tree is indigenous to North America, where it is commonly seen growing along riverbanks and streams. It is easy to recognize in the summer when the female cottonwood tree dispenses seeds attached to white fiber type fluffs that resembles cotton. Planting cottowood tree seeds is an easy process, but you must plant the seeds within two to three days after you collect them. Otherwise the viability of the seeds can plummet.
Gather the seed capsules of a cottonwood tree before they dry and crack open. This is usually in June or early July.
Place the cottonwood capsules into a fine-mesh wire colander or sieve. Put the sieve or colander in a warm location in your home where it will remain undisturbed. Let the capsules dry in the colander or sieve until the capsules start to crack open. This can take as little as three or four days or as long as a few weeks, depending on the temperature.
Rub the capsules across the surface of the colander or sieve to separate the cottonwood tree seeds from the capsules. Do this once the capsules have dried and are cracked open.
Fill up a seed flat or similar type of container with a good quality seed-starting planting mix. Or if you want to make your own, measure out equal amounts of vermiculite, perlite and peat moss. Mix the three ingredients together until they are well blended. You can purchase a seed flat at your local plant nursery or garden center.
Tamp down the seed raising mix in the tray using the base of a 4-inch pot. Then, use the long side of 12-inch ruler to level off the contents in the seed flat.
Create shallow rows, no more than 1/8 inch deep, in the seed flat. Each row should be about 1 1/2 inches apart. Place one cottonwood tree seed every 1 inch in each of the shallow rows. Then, press the cottonwood tree seeds into the soil ensuring good seed-to-soil contact.
Transfer the seed tray into a light-filled temperate area in your home. Placing the tray near a window that faces south, or southwest is ideal. But do not place the tray where there will be any sunlight directly upon it. The temperature range should be between 60 and 70 degrees F.
Mist the entire contents of the seed tray until it is thoroughly saturated with water. Cottonwood tree seeds will typically being germinating within a few hours, so it's essential the germinating media remains moist but never sodden wet. You can transplant the cottonwood saplings into 4-inch pots, or larger pots, when they are approximately 1 to 1 1/2 inches tall.