Summarize:

Rhubarb doesn't do well in intense heat, so once you've soaked the seeds and planted them in a soil-filled pot, you'll need to find a shady area for them. Either put the pot in a shaded spot outdoors or keep the pot indoors. This way, the seeds will stay healthy during hotter months as they're growing into plants. Transplant the plants to the garden after about 30 days in the pot. At this point, they should be about 4 inches tall. Carefully tip the pots upside down until the plant and root ball slide out. Dig a hole that's twice as wide as the plant. Plant the root balls as deep as they were in their pots. To get the plants out of the pot, it helps if you water them an hour or so beforehand. If the root ball doesn't come out with a little squeeze to the sides of the pot, you can use a butter knife to cut around the soil. If you used a peat pot or a cow pot you can simply place the pot with the plant into the soil. To avoid overcrowding the plants, clear out enough space in the ground so that you can plant the seeds 36-48 inches (90-120 cm) apart. Consider planting the rhubarb on a raised bed or in a hillside to avoid drainage issues.
Start your seeds in August in a shady location. Transplant the plants to the garden once they're 4 inches (10.2 cm) tall.