Marshmallow has many uses! Use the leaves and flowers as poultices to soothe skin irritations, bruising, and irritation. Make a tea of the leaves and flowers for bronchitis and cough. The roots contain more than 30% mucilage that is soothing to mucus membranes and the digestive tract. The leaves, when harvested in early spring, make a mild tasting and healthy salad. Plus the mucilage is what gives marshmallow (the confection) its light and airy texture.
Start seeds in fall or in very early spring if you have harsher winters. If no cold weather is coming, seeds need to go through "stratification" - put moist soil or sand and seeds into a ziplock plastic bag and let it sit out on the counter for 24 hours. Then move to the refrigerator for 4-6 weeks - you can remove them when you see germination.
Plant seedlings in a seed tray with a domed cover to retain moisture - once your seedlings are 3-4" tall and have at least 2 true leaves, they can be planted in their permanent location.
Choose a final location that is sunny and damp - marshmallow can survive conditions that many other flowers cannot! Plant seedlings 1' apart and mulch well to retain moisture and prevent weeds - since it is a perennial plant, chose a good long term location.
Marshmallow can get 3-4' tall so plant where it will not shade other plants.
Avoid harvesting roots for use until the plant is well established - at least fall of the second year. Harvest leaves anytime for salads or poultices.
If preserving roots/leaves for the winter: Harvest the leaves after flowering. Dry them well. Harvest the root in late fall, before the ground freezes. Clean the roots of fibers and cork. Chop roots into 1⁄2" pieces and dry immediately.