How to Grow and Care for Marshmallow Plant

Marshmallow plant with small white flowers and spiky leaves on stems

The Spruce / Autumn Wood

The marshmallow candy we all know and love is based on a confection made by the ancient Egyptians from the root of Althaea officinalis. Today's marshmallows, however, no longer contain any trace of the plant, they are grown as ornamentals.

Marshmallow plants grow 4 to 5 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.

Common Name Marshmallow, marsh mallow
Scientific Name Althaea officinalis
Family Malvaceae
Plant Type Perennial, herb
Mature Size 4-5 ft. tall, 2 ft. wide
Sun Exposure Full
Soil Type Moist
Soil pH Acidic, neutral, alkaline
Bloom Time Summer
Flower Color White, pink
Hardiness Zones 3-7 (USDA)
Native Areas Europe, Asia, Africa

Marshmallow Plant Care

The plant is generally easy to care for and an excellent option for wet gardens.

Because marshmallows like full sun, be careful not to plant them somewhere in which taller plants will crowd them out. And, while they like moisture a great deal (that's where the "marsh" part comes from), it's important that the soil in which they are planted has good drainage.

You can either plant marshmallow 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 12 inches apart and mulch heavily to keep weeds at bay. Keep the area free of weeds until the plants are tall and established and then they'll mostly be able to fend for themselves.

Marshmallow plant with small white flowers and spiky leaves on tall stems

The Spruce / Autumn Wood

Marshmallow plant with small white flowers on stems with spiky leaves closeup

The Spruce / Autumn Wood

Marshmallow flower with small white petals and purple stamen closeup

The Spruce / Autumn Wood

Light

Marshmallow plants need full sun, they do not do well in the shade.

Soil

True to its name, the marshmallow likes marshy, wet areas. If there's a spot in your yard where the soil stays damp this may be a good place to grow these plants.

Marshes also have slightly acidic conditions. To create a slightly acidic, moisture-retaining sandy loam mixture, you can add sand and compost, including used coffee grounds. But don't worry too much about getting acidic conditions, though, as these flowers are not really fussy about pH levels.

Water

Moisture is essential for marshmallow 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 may 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 for your marshmallows.

Temperature and Humidity

Marshmallows 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, rise again in the spring.

Fertilizer

Marshmallow 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 marshmallow plants, but it is a good idea to deadhead spent flowers and remove any dead leaves to keep them from attracting unwanted pests.

Propagating Marshmallow

Marshmallows are easy to propagate by root division:

  1. Simply wait for the plant to go dormant in the late fall or early winter before the ground freezes. Dig up the plant with its entire root system.
  2. Divide the root mass using a sharp spade. Replant the sections in a new location and mark it well.

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 Marshmallow Plants From Seeds

Marshmallow 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, start the seeds indoors three to four weeks before the last frost date, or sow outdoors once the danger of frost has passed.

Sow them in groups of five or six seeds, in groupings 18 to 24 inches apart. Lightly cover them 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 marshmallows 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 marshmallow 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 reemerge in the spring.

Common Pests and Plant Diseases

Even though nearly all parts of the marshmallow plant are edible, it is mostly left alone by pests. One invader that might decide to feast on your marshmallows, however, are flea beetles, small brown, black, or grey bugs that could lay their eggs near the plant's roots, which provide nourishment for the larva. The larvae then can feed on the leaves, leaving pinprick-sized holes. If the problem arises, you can deal with it using any pesticide labeled for flea beetles.

In terms of diseases, marshmallows are similarly resistant, except for rust, a fungal condition that sometimes plagues the plant. It presents 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 watering the plant from the top down and apply a copper-based fungicide.

Common Problems With Marshmallow

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 keep the soil from drying out.

How to Get Marshmallow to Bloom

If your marshmallow 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.

FAQ
  • Is marshmallow and mallow the same?

    The plant is sometimes confused with two other plants, the common mallow (Malva sylvestris) and tree mallow (Lavatera). Unlike common mallow, marshmallow has multiple stems, fuzzy down on its stems and foliage, and blush-colored flowers. Marshmallow flowers are smaller, paler, and more numerous than the common mallow. Lavatera's flowers are a bright shade of cotton candy pink and the leaves are spiky.

  • How do I harvest marshmallow roots?

    They can be harvested in the late fall after the plant has gone dormant. Remove the roots you'll need for your purposes, then replant the crown because the plant can continue to grow. Clean and dry the roots and then use them as you like (boiling creates the gelatinous substance and texture marshmallows are famous for). Be sure not to harvest roots from plants that are younger than two years old.

  • Is marshmallow plant invasive?

    Marshmallow plants reseed themselves, yet are not considered invasive. You may see them growing along a marshy roadside or in a meadow, and sometimes a volunteer will pop up in a home garden.

Article Sources
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  1. Althaea officinalis. Missouri Botanical Garden.