Marsh mallow plants grow four to five feet tall and can put on quite a dramatic show in the garden while in bloom. Their tall elegant spikes are covered with almost white to blush or light pink flowers from July to September. They’re also loved by pollinators. Brown seed pods begin to form in late September, releasing tiny black seeds when mature. Depending on your climate, they can be planted from seed in the fall or spring. Because marsh mallows like full sun, be careful not to plant them somewhere in which taller plants will crowd them out. And, while they need moisture (that’s where the marsh part of the name comes from), it’s important that the soil in which they are planted has good drainage. You can either plant marsh mallow seeds directly in the ground in the late fall if your area has mild winters, or in the early spring if your winters tend to be frosty. In either case, you’ll want to plant the seeds about 18 to 24 inches inches apart and mulch the plants heavily to keep weeds at bay. Keep the area free of weeds until the plants are tall and established and then they’ll be able to fend for themselves.
Light
Marsh mallow plants need full sun, they do not do well in the shade.
Soil
True to its name, the marsh mallow plant likes marshy, wet areas. If your property has an area with consistently damp soil and with full sun, this plant will be happy if you plant it there. Marshes also have slightly acidic conditions. To create a slightly acidic, moisture-retaining sandy loam environment, you can add sand and compost to the soil, including used coffee grounds. But don’t worry too much about achieving acidic soil conditions, though, as these flowers are not fussy about pH levels.
Water
Moisture is essential for marsh mallow plants. If you’re trying to grow them in an area that tends to stay dry, they very likely won’t flourish. However, standing water areas might be too wet for them. The plants do need a fairly consistent state of moisture. Using moisture-retaining soil amendments such as organic matter can be advantageous. If your plants return the year after planting, you’ll know the moisture levels are hospitable.
Temperature and Humidity
Marsh mallows tend to be tough plants and can thrive in a variety of different climates and humidity levels. They are extremely cold tolerant although, during sub-freezing temperatures, they will die back. They will, however, emerge again in the spring.
Fertilizer
Marsh mallow plants grow in such a wide range of soils (they can even tolerate salty soil), that applying a special kind of fertilizer isn’t really necessary, especially if you have already added organic matter to the soil.
Pruning
It’s not strictly necessary to prune marsh mallow plants, but it is a good idea to deadhead spent flowers and remove any dead leaves to prevent them from attracting unwanted pests.
Propagating Marsh Mallow
Marsh mallows are easy to propagate by root division: Propagation by division can also be carried out in the early spring before greenery has begun to sprout although, because the plants die back in the winter, it could be difficult to find them before they start growing.
How to Grow Marsh Mallow Plants From Seeds
Marsh mallow plants can be easily planted from seed. It’s not very common to see them for sale in a garden shop, but you can order the seeds online. The seeds need cold stratification before planting, mimicking their cycle in nature. You can place your seeds in the refrigerator for a few weeks, whether in their package or in a plastic bag with some lightly-moistened peat moss. This will mimic the winter dormancy period needed for the seeds to germinate. After the cold stratification period, start the seeds indoors three to four weeks before the last frost date, or sow them outdoors once the danger of frost has passed. Sow them in groups of five or six seeds spacing 18 to 24 inches apart. Lightly cover the seeds with soil, and keep moist until they germinate. This usually takes about three to four weeks. Once established, these hardy plants will return every year.
Potting and Repotting
Growing marsh mallows in containers is not recommended as the plant needs consistently wet soil, which is difficult to maintain because container plants dry out much faster than garden soil.
Overwintering
As marsh mallow is extremely cold tolerant and dies back in the winter months, there is no need to take any special precautions for overwintering. It is, however, always a good idea to cut away any dead branches or leaves to keep your garden tidy and increase airflow around the plants when they re-emerge in the spring.
Common Pests and Plant Diseases
Even though nearly all parts of the marsh mallow plant are edible, it is mostly left alone by pests. One invader that might decide to feast on your marsh mallows, however, are flea beetles. Flea beetles are small brown, black, or grey insects that could lay their eggs near the plant’s roots, which provide nourishment for the larva. The larva then can feed on the leaves, leaving pinprick-sized holes. If the problem arises, apply neem oil, which is organic. In terms of diseases, marsh mallows are similarly disease-resistant, except for rust, a fungal condition that sometimes plagues the plant. It presents itself as raised white dots on the underside of leaves which eventually turn orange, then yellowish-green, and finally black. If you see this condition, remove any affected leaves, avoid overhead watering and apply a copper-based fungicide.
Common Problems With Marsh Mallow
The only problem you might have with this hearty plant is a lack of water, which will cause them to die. So you’ll either want to plant them in an area that is naturally moist or keep them on a steady watering schedule to prevent the soil from drying out.
How to Get Marsh Mallow to Bloom
If your marsh mallow plant fails to bloom, the reason is most likely lack of sun. Move it to a location where it gets full sun, or, if possible, prune surrounding plants that cast shade on it, to let in more sunlight.
