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. A colorful pot of foliage with a sprinkling of little starry flowers for the windowsill? You know the answer. 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. Find all you need to know about how to plant oxalis bulbs right here.

Choosing a Growing 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 much 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 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; 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 and warm (60+ degrees), spring, summer or early fall. Indoors, plant your oxalis bulbs whenever your windowsills look bare.

How to Plant Oxalis Bulbs

Loosen your soil and poke the little bulbs down about 1 to 1 ½”. Don’t worry about which end is up; it doesn’t matter with oxalis. Plant about 1-1.5" apart or about 8-10 bulbs in a 6" pot. 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 outdoors, 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. How often to water indoors depends on temperature and air flow. Hot, dry rooms - think forced air heat - will cause the soil to dry out faster. The goal is to keep the soil very lightly moist. 

At the Season’s End

In zones 7-10, simply leave your oxalis in the garden; they’ll generally overwinter successfully, barring unusually cold weather or soil that doesn't drain. For varieties hardy to zone 6, a layer of mulch adds a bit of extra protection. In our experience, the purple triangularis oxalis are the most winter hardy.  

In colder regions, there are three choices. First, you can treat oxalis like annuals and replace in the spring. Second, you can wait until the foliage yellows, lift the bulbs, trim off the leaves and store in in very 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 them as houseplants.

Note that windowsill-grown oxalis often go through a winter dormancy period when the foliage dies back and the plants sleep for a month or two. During this period ease up on watering, providing just enough moisture to keep the soil from being bone dry. Overwatering while the plants aren't actively growing can lead to bulb rot.

Oxalis Safety Note:

Recently, oxalis bulbs have cropped up on Amazon, EBay and other international websites. Many of these bulbs ship from China. Foreign plant stock sent directly to buyers is not inspected for disease, insects or pathogens. Ordering from uninspected sources endangers your personal growing environment and also risks introducing imported non-native invasive species and diseases into our country.  Examples of catastrophic introductions include Dutch Elm disease, Japanes beetles, kudzu, emerald ash borer, chestnut blight, etc.  

You don't want to be responsible for the next invasive species crisis, right?  Invasive Species

Our plant stock - oxalis and all other - is USDA and CA Ag Dept. inspected and certified clean and disease and pest free.

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. A little here or there probably isn't a problem (these plants are edible for humans in small quantities) but in big or multiple bites, 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 facing windows or ones with dappled light. Give Iron Cross a bit more sunlight to avoid legginess; this variety does best with a half day of sun, preferably morning sun, in most regions of the country. If your oxalis stems are a bit long and leggy, which can be a response to insufficient sunlight, try moving them to a spot where they'll get more sunlight.
  4. In our experience, the purple triangularis oxalis are the most vigorous for over wintering cultivar in zones 6 and warmer. And, the Iron Cross plants tend to like a bit more water than some of the other oxalis, which aligns with their preference for a bit more sunlight.
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Success Snapshot

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

Soil: Average

Depth: Cover with 1-1 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:

How Many Bulbs per Pot?

Need a recommendation for the number of oxalis bulbs to plant based on pot size? Here you go!

Pot size – 4"5-7 Tubers
Pot size – 6"6-8 Tubers
Pot size – 8"10-14 Tubers 
Pot size – 10"15-20 Tubers