Cleomes, also known as spider flowers, are tall flowering annuals that are often grown in large batches in one area. For this reason, and because it is a more economical option, cleome is often grown from seed. The best time to grow cleome is the in the spring. They need an area in full sun, as well as rich, well-draining soil to thrive. To improve germination, refrigerate cleome seed packets for five days before sowing them.
Wait until a month before the last anticipated frost of the spring. In most zones, this occurs sometimes in mid-spring.
Test the soil pH level with a soil testing kit and add sulfur or limestome to lower or raise the acidity. Use the recommended dosing to achieve a soil pH between 5.5 and 5.8, which cleomes prefer. Dosing is based on how much you need to change the pH and what type of soil conditions you have (e.g., sandy, clay).
Incorporate about 2 inches of peat moss, compost or another similar organic matter to the top 6 inches of soil to help improve water drainage and add valuable nutrients to the soil.
Scatter the seeds on the ground by broadcasting them with your hands. A 1 oz. seed package will cover about 125 square feet.
Rake the seeds in lightly or spread a little bit of vermiculite on top to help the seeds retain moisture--but the seeds must also still be exposed to light in order to germinate.
Water the area with about a 1/2 inch of water and keep the area slightly moist. The seeds usually germinate in about two weeks, but may take longer.