Considered endangered or threatened in some US states, the branched, or branching, bur-reed grows in shallow portions of still waters or along the edges of slow-moving streams. The branched bur-reed is typically found in the middle to eastern portions of the North America. With a preference for full sun, the branched bur-reed can be found growing in rich soils which stay consistently wet along the roots.
Check the plastic tray to make sure there aren't any cracks or holes in it which would prevent it from holding water. Set up your tray on a flat, level area, floor or table, of your greenhouse.
Add potting soil to your pots and fill them up to 1/2 inch from the top rim of the pot. Arrange the pots within the plastic tray so they all rest flat, and are not crammed into the space. Use a second tray, if necessary.
Pour enough water into your tray to create an inch of standing water. Check the tray in about an hour to see what has been absorbed. As the soil continues to absorb, keep refilling the tray until you have one inch of standing water and the pots are saturated.
Place a few seeds 1/4 inch deep into the moist soil and cover over. Check the seeds every two to three days to look for germination and make sure there is still water in the tray, adding when needed.
Increase the depth of your standing water by 1/2 inch every couple of weeks to keep up with the increased amount of water the bur-reed plants need to grow. As the plants get taller, the water level should rise.
Set your tray with seedlings into a cold frame as spring arrives and let them harden off and become accustomed to outdoor conditions throughout the spring. Continue to monitor the water levels to keep up with steady growth.
Select a sunny location around a pond, marsh, or swampy area for the seedlings to go and plant them along the edges in the summer time. The plants can live in areas of similar to slightly deeper water depth, as compared to what you have been giving them.