Plants that grow from rhizomes, underground stems also known as rootstocks, can be either a blessing or a curse in the garden. They are a blessing when desirable plants such as groundcovers spread into a thick mat that crowds out weeds. They are a curse when weeds and invasive species use the same underground growth to take over a yard. Gardeners encounter rhizomes in vegetable beds, flower borders, lawns, and even the cracks of a driveway. Knowing how rhizomes work helps gardeners care for the plants they want and control the ones they do not. The distinction matters because rhizomes are stems, not roots, and they behave like neither.
What Are Rhizomes?
A rhizome is a horizontal stem that grows underground, sending roots downward and shoots upward from its nodes. Ginger, turmeric, iris, and bamboo all grow this way. Unlike upright above-ground stems, rhizomes store energy, produce new plants, and spread the parent plant horizontally. Botanists describe them as modified stems because they carry out more functions than a typical stem. The term rootstock should not be confused with the rootstock used in grafting, which refers to the lower part of a trunk or stem that a scion is attached to.
How Rhizomes Differ From Roots and Stolons
True roots absorb water and nutrients and do not produce shoots along their length. Rhizomes are thicker, jointed, and capable of sprouting new plants at every node. Stolons are similar runners that grow above ground, as seen in strawberry plants, while rhizomes stay below the surface. The difference is visible when a plant is dug up: rhizomes show distinct nodes, buds, and often small scale leaves. The jointed structure even shows up in the name, since the word rhizome comes from a Greek term meaning rootlike.
Why the Distinction Matters
Gardeners who mistake rhizomes for roots make two common errors. They cut the rhizome into pieces while weeding and leave fragments behind that each sprout into a new plant, or they plant a rhizomatous species in open soil and then fight it for years. Identification drives both care and control.
Rhizomes grow horizontally just beneath the soil surface, and the depth varies by species. Some stay within the top few inches, while others, such as Japanese knotweed, can push several feet down. The carbohydrates stored in a rhizome let the plant survive drought, freezing, and repeated cutting of its above-ground growth. That reserve is exactly what makes rhizomatous weeds so hard to kill.
How to Identify Rhizomatous Plants
Look for the signature signs. Rhizomatous plants spread outward from the original clump, so a single planting becomes a widening patch over time. The stems that emerge from the ground may appear unrelated, but digging down shows they are connected by a horizontal stem with nodes and buds. Species with thick, fleshy underground stems such as iris and ginger are easy to recognize, while grasses and bamboos hide the same structure in thin, wiry rhizomes.
Quick Identification Checks
- Dig around the edge of the clump and look for horizontal stems with nodes.
- Check whether new shoots appear at a distance from the mother plant.
- Feel the underground stem: rhizomes are firm and jointed, not hair-like.
- Look for scale leaves or small buds along the buried stem.
- Note how fast the patch grows from one season to the next.
Clumping vs. Running Growth
Not all rhizomatous plants behave the same. Clumping types, such as bearded iris, keep their rhizomes short and stay where they are planted. Running types, such as bamboo and quackgrass, push rhizomes far from the parent plant and colonize new ground quickly. That single trait decides whether a species is a reliable garden plant or a management problem.
Timing helps with identification. In spring, new shoots from a rhizome system emerge in a ring or a widening front around the original planting. In fall, the underground stems are easiest to see because the soil is still workable and the foliage has died back. A garden journal that notes where and when shoots appear makes the pattern obvious over two or three seasons.
Plants That Grow From Rhizomes
Rhizomatous species span the useful, the ornamental, and the invasive. Plants grown for their edible rhizomes include ginger and turmeric; potatoes, often grouped with them in kitchen gardens, are technically tubers formed from swollen underground stems. The table below sorts common examples by how gardeners actually use them.
| Category | Examples | Growth Habit | Garden Value or Risk |
|---|---|---|---|
| Edible | Ginger, turmeric, potatoes (tubers) | Fleshy underground stems | Culinary crops with long harvest windows |
| Ornamental | Bearded iris, canna, lily of the valley, pachysandra | Clumping to spreading | Flowers, foliage, and weed-suppressing groundcover |
| Invasive | Japanese knotweed, quackgrass, Bermuda grass, running bamboo | Fast-running rhizomes | Difficult to remove once established |
Groundcovers such as pachysandra and lilyturf form the dense mat that gardeners rely on to suppress weeds, exactly the behavior that makes rhizomes valuable. The same behavior makes Japanese knotweed one of the most expensive invasive plants to remove, because its rhizomes reach several feet deep and resprout from any fragment left in the soil.
Lily of the valley and pachysandra are planted precisely because their rhizomes knit the soil together on slopes and under trees where grass struggles. The trade-off shows up later: the same knitting makes them hard to remove when a bed is redesigned, since every rhizome piece left behind starts a new colony.
Rhizomes in the Kitchen Garden
Ginger and turmeric grow from plump rhizomes planted just below the soil surface, and they reward warm, moist conditions with long growing seasons. Potatoes are planted as seed pieces, each containing at least one eye, and the underground stems swell into the tubers that are harvested months later.
Rhizomes in the Ornamental Border
Bearded iris rhizomes sit partly exposed at the soil surface and flower best when divided every few years. Canna and calla lilies are tender rhizomatous plants in cold climates, dug up in fall and stored indoors until spring.
Caring for Plants With Rhizomes
Care for rhizomatous plants comes down to planting depth, division, and seasonal timing. Most rhizomes want shallow planting, 1 to 2 inches deep, with the top of the rhizome near the surface. Deeper planting encourages rot and delays flowering in many species. Woody rhizomes from trees and shrubs need different treatment, and ornamental grasses respond best to a spring cutback before new growth emerges.
Division Keeps Clumps Healthy
- Dig up the clump in early spring or fall when the plant is dormant.
- Shake off the soil and cut the rhizomes into sections, each with roots and at least one shoot or eye.
- Discard old, woody centers that have stopped producing growth.
- Replant the divisions at the correct depth and water them in well.
- Divide every two to three years to keep the planting vigorous.
Division does double duty: it renews the plant and produces free transplants for other parts of the garden.
Division timing follows the bloom. Spring-flowering plants such as iris are divided in summer after flowering, while fall bloomers such as canna are divided in early spring. Cutting the rhizome with a clean knife reduces the chance of rot, and dusting the cut ends with sulfur helps them heal in humid weather.
Watering and Feeding
Rhizomatous plants establish best with consistent moisture in the first season. A balanced fertilizer applied in spring supports the growth spurt, but heavy summer feeding can push soft growth that invites pests. Tender rhizomes such as canna and ginger are lifted in fall in cold zones, dried briefly, and stored in a cool, dry place until replanting.
Managing Invasive Rhizome Spread
Controlling a running rhizome system takes persistence, because every piece left behind can resprout. The method that works depends on the species and the size of the infestation. Small patches can be dug out in an afternoon; established stands can take years to clear.
Physical Control Methods
- Dig out the entire root system, screening the soil for fragments.
- Install a root barrier 24 to 30 inches deep around garden beds.
- Grow running bamboo in containers or behind a barrier to contain the rhizomes.
- Cut or mow shoots repeatedly to starve the rhizomes of energy.
When Herbicides Are Justified
For established stands of knotweed or quackgrass, repeated herbicide applications timed to the plant’s growth cycle are often the only practical option. Late summer applications, when the plant is moving energy back into the rhizomes, deliver the chemical where it does the most damage. Follow-up treatments are usually needed for a second season.
Combining methods improves the odds. Digging in spring, when the rhizomes are full of stored energy, weakens the plant; repeated cutting through the summer starves the regrowth; and a late-season herbicide application finishes the job. Skip any one step and the system rebounds the next year.
Prevention Beats Removal
The cheapest control is choosing clumping species in the first place. Gardeners who know a plant’s growth habit before buying avoid the years of labor that come with an aggressive runner. The same vigilance applies to shared property lines, since a neighbor’s running bamboo does not stop at the fence.