Mimulus will grow best in full sun. The soil should be moist as the plants like to grow in wet ground. Avoid high temperatures and drying out in drought periods. Plant out any time after May; or plant out in late September for over-wintering plants to flower early in the succeeding spring.
Mimulus are ideal for planting in containers and in fact they thrive in a pot.
Starting from seed:
Sow mimulus indoors in late winter or early spring. Choose a container, such as a one-cell planting pack, that has drainage holes. Fill it to within a half inch of the top with a slightly moist, sterile seed-sowing mix. Press the fine seeds into the mix, but do not cover them.
Soak the mix from the bottom up, by setting your container in a flat that contains an inch or so of lukewarm water. Wait a couple of minutes until the surface of the mix has absorbed enough water to be damp, but not soggy.
Remove the container from the flat and cover it loosely with plastic wrap. Set it in a warm, bright spot, such as under grow lights. Expect the seeds to germinate in one to three weeks. Remove the plastic wrap when they begin to sprout, but continue to water as necessary from the bottom if the soil begins to dry out.
Separate the seedlings, once they are large enough to handle, and transplant them into cell packs filled with a mixture of half seed-starting mix and half potting soil. Pick up the seedlings by their leaves to avoid breaking their stems.
Allow seedlings to harden off for a couple of weeks before planting by exposing them gradually to a little more sun outside every day.
Select a location, in either your garden or window box, that gets sun to partial or bright shade. Pick a shady spot if your summers are hot. Look for an area where the soil stays continuously damp. After all danger of frost has passed, plant the seedlings about six inches apart.
Pinch out the tips of the plants to encourage them to branch. Snip off the flowers when they fade, to keep your mimulus blooming. Never allow the soil to dry out completely.