Both woodland and Chinese forget-me-not plants are best sown in sunny or lightly shaded locations with moist, humus-rich soil. Soil should be neutral or slightly acidic. Prepare the soil by mixing it with compost or other rich organic matter. Soil temperature should be around 68 degrees Fahrenheit for germination. Place the woodland species 8 to 10 inches apart, and the Chinese species 10 to 12 inches apart when sowing directly in soil. Thinning is not absolutely necessary; forget-me-not flowers will thrive even in crowded conditions.
You can plant forget-me-not seeds throughout the seasons, but a springtime planting is best. If frost is a risk, sow seeds indoors or wait until the risk is past, then transplant outdoors later in spring. If they are planted in late summer in a cold climate, protect them in a greenhouse through winter so they can be placed outdoors in spring. For continuous blooms, plant seeds along with transplants in spring. These flowers will readily reseed themselves and spread through your garden. To avoid this and control their spread, remove dead blooms.
When starting indoors, plant seeds in seed flats and move to individual pots once they have germinated and are established. Transplant to the garden once they reach 3 or more inches in height. Forget-me-nots thrive near spring beds, water gardens, bulb gardens, flower garden edges and any area where they can receive plenty of moisture. If planting near water, protect the roots with rocks so they do not wash away.
Forget-me-nots are sprawling plants with a range of heights. Some reach 6 to 8 inches high, while Chinese variety can grow up to 2 feet tall. The moisture-loving plants may not produce blooms during hot periods such as August. They often form dense patches and, because of their self-sowing ability, will continue to bloom in wildflower gardens every spring. Naturally you may find forget-me-nots growing along roadsides and open woods, or under dense forest canopies, wherever there is sufficient moisture.