Are they the vining type or the bush variety? The common name moonflower refers both to Datura inoxia and Ipomoea alba.

Datura is the shrub and can be sown in early spring. They benefit from some cold, but mine sown in the dead of winter never sprouted. The seeds are about 1/4" across and flat, shaped like a kidney. Other daturas are tiny black almost round seeds, in case it's not D. inoxia.

Moonvine is a tender annual and should be sown once all chances of frost have passed. These seeds are usually larger, pale tan or dark brown and very hard.

jlhart: I love moonflowers, and you will too if you plant them where you can see and enjoy them at night. The flowers look like big white moons. Because moonflowers are vines, they can grow 12-18 feet in a year. You will get more enjoyment if you provide something for them to climb.

You can sow moonflower seeds in your garden (called direct sow or DS) after all danger of frost is past. Cover seeds with 1/4" soil and water thoroughly.

You can also start seeds indoors 3-4 weeks before the last frost - this gives you a faster start. After planting, water thoroughly.

Either way, moonflower seeds germinate easily and grow quickly. Thin or space your plants to at least 6" apart.

The link below provides more info about how to grow moonflowers.

Here is a link that might be useful: How to Grow Moonflower Seeds