How to Plant Oxalis Bulbs and Rhizomes
Knowing how to plant oxalis bulbs as well as how and when to lift and overwinter them indoors is an important part of growing these lush foliage plants at home.
Sometimes called shamrocks or false shamrocks, oxalis species, such the iron cross shamrock (Oxalis deppei) and purple shamrock (Oxalis triangularis), are widely grown as houseplants and as outdoor ornamental plants within USDA plant hardiness zones 8 to 11.
Although they grow best under cool conditions, oxalis plants will not tolerate cold. They must be planted in spring, and the bulbs must be lifted and overwintered indoors in colder climates outside their preferred hardiness zone range.
All parts of oxalis plants are mildly poisonous, especially to horses.
Common Varieties of Oxalis
Most common oxalis species resemble each other, but there are notable differences among them. Some species have bulbous roots called "pips," while others have carrot-like rhizomes.
All oxalis species share a similar sensitivity to cold conditions, and the plants need to be lifted from the ground regardless of whether they have bulbs or rhizomes.
Planting Oxalis Bulbs or Rhizomes
The process of planting oxalis bulbs or rhizomes should be done in spring after all frost danger has passed, regardless of whether you are planting them in the garden or in pots to be grown indoors.
Oxalis can be invasive, so consider installing a root barrier around the bed where the plant is growing.
Planting Oxalis in the Garden
Oxalis plants are sensitive to strong sunlight and dry conditions, so choose a planting site in a lightly shaded area of the garden with moist, fast-draining soil.
- Amend the bed with a 3- to 4-inch-thick layer of compost worked into the top 6 to 8 inches of soil.
- Incorporate slow-release, high-nitrogen fertilizer, such as 12-6-6, into the bed at a rate of 2 pounds per 100 square feet of area.
- Dig a planting hole that is just deep enough to hold the bulbs. Set the bulbs in the hole horizontally.
- Plant the bulbs or rhizomes so that they are just below the soil surface; the root structure should neither be exposed nor deeply covered with soil. Space them 8 to 12 inches apart.
- Water the oxalis deeply after planting. Spread a 1- to 2-inch-thick layer of mulch over the planting site.
Planting Oxalis in Pots
Potted oxalis plants need plenty of moisture but also good drainage, so choose high-quality potting soil with perlite and a pot with at least one drainage hole at the base.
- Fill the bottom half or two-thirds of the pot with potting soil. Nestle the rhizomes or bulbs into the soil horizontally.
- Add soil to the pot until the bulbs or rhizomes are completely covered but resting just below the surface of the soil.
- Water well after planting the oxalis bulbs or rhizomes. Add water until it runs freely from the base of the pot.
- Set the pot in a bright, sunny location with some midday shade. Dappled light all day works well too.
Clay pots are a good choice for growing oxalis, because the material absorbs water and can help regulate soil moisture levels.
Overwintering Oxalis Bulbs
In colder climates, oxalis bulbs need to be overwintered indoors. Potted oxalis plants can simply be brought indoors and kept in a cool, bright room, while oxalis plants grown in the ground must be dug up and the bulbs or rhizomes stored indoors.
- Prepare the bulbs for overwintering in late summer or early autumn after the foliage has dried up and died back.
- Cut back the foliage to ground level using pruning shears. Dig up the bulbs or rhizomes using a garden fork or a short shovel.
- Remove the caked-on dirt from around the bulbs, but do not break apart the bulb cluster.
- Store the bulbs in a paper bag or box filled with dry material, such as vermiculite, sawdust, coir or sphagnum moss.
- Place the storage container in a cool, dry and dark location where temperatures stay between 40 and 50°F.
- Replant the bulbs in spring after all frost danger has passed.
- Many oxalis varieties go through several dormancy periods in a year where the plant appears to die. Pinch off the dead leaves and stop watering. The plant will resume growing again in about three months.
- Fertilize potted oxalis once a month when it is not dormant with a standard houseplant fertilizer.
- Oxalis does not tolerate dry conditions. Water more often during hot, dry weather if the plant is not in its dormant stage.
Sasha Degnan holds a Bachelor of Arts degree in English Literature and Anthropology. Her written work has appeared in both online and print publications. She is a certified Master Gardener and dedicated plant enthusiast with decades of experience growing and propagating native and exotic plant varieties.