Oxalis / Shamrock Planting Guide

These plants have become our garden equivalent of that much-loved little black dress, go-tos for all sorts of planting events. Need a colorful edge along a pathway or stone walk? Oxalis. How about filler in a mixed container, something with purple leaves or pinwheel form? Oxalis. Or a ruffle around the base of an upright partner, like a large flowering amaryllis? Yep, oxalis. If you can envision it, these little guys can pull it off.

Speedy to sprout, fast to flower and good to grow in most any part of the country – add oxalis to your short list.

Planting Information

Choosing a Site

Choosing a site with optimum sunlight for oxalis depends on the region in the country where you garden and the variety you are planting. Oxalis iron cross is happy with sun most of the day and appreciates a bit of afternoon shade in the hottest regions. Other oxalis do best with dappled shade early in the day and no direct sun in the afternoon. Indoors, this means that an east facing window is often a good choice.

Soil Prep

If you are planting in the ground, look for a site that drains well. Oxalis are happy in average soil and bulb rot is a risk in soggy soil. A pelleted, slow release fertilizer provides nutrients throughout the growing season. Planting in containers? Any standard potting mix will work well.

When to Plant Oxalis

Plant outdoors in spring when frost danger has past and soil has warmed. In zones 7-10, plant any time the soil is workable, spring, summer or early fall.

How to Plant Oxalis Bulbs

Loosen your soil and poke the little bulbs down about 1 ½”. Don’t worry about which end is up; it doesn’t matter with oxalis. Plant about 1-1.5" apart. They’ll sprout and grow well from any position. After planting, water well to settle the soil around the bulbs. Sprouts typically appear within 2 weeks. Easy peasy.

During the Season

In well drained soil, oxalis need about 1” of water a week from rain, irrigation or a combination of the two. Watering every 3-4 days is usually ideal; keep an eye out for wilting behavior. Be aware of the number of days you've gone between waterings and if wilting is evident, you've gone a day too long. Once you have the pattern down, your oxalis will produce a sea of tiny flowers on thread-like stems for months with next to no care.

At the Season’s End

In zones 7-10, simply leave your oxalis in the garden; they’ll overwinter successfully. For varieties hardy to zone 6, a layer of mulch adds a bit of extra protection. In colder regions, there are three choices. First, you can treat your oxalis like annual and replace in the spring. Second, you can wait until the foliage yellows, lift the bulbs, trim off the leaves and store in in slightly damp peat in a cool (45-55 degrees), dark place. Or, you can bring potted oxalis indoors when the weather cools, place next to a sunny window and enjoy as a houseplant.

Insider Tips

  1. Budding horticulturalist in the house? Let them plant oxalis. Easy, fast, colorful and never fussy.
  2. Don't let your pets chew on oxalis. The oxalate crystals in the leaves and bulbs can damage kidneys.
  3. Site your potted oxalis based on sunlight preferences. Place purple triangularis and green regnelli in east racing windows or ones with dappled light. Give iron cross a big more sunlight to avoid legginess.
  4. Oxalis tirangularis, regnelli and Fanny thrive in similar conditions - feel free to mix the bulbs togeher for a colorful custom blend.
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Success Snapshot

Light: Morning sun; afternoon shade in hottest areas (see variety specific details, left)

Soil: Average

Depth: Cover with 1-2" of soil

Water: Average moisture

Uses: Containers, borders, hanging baskets and along walkways

Tip: Oxalis are the ultimate mixers; poke a few bulbs into most any container creation

GUIDE: Oxalis or Shamrock Planting Guide

They Start Out looking Like This: