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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 for 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.
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.
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.
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. Indoors, plant whenever your windowsills look bare.
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.
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.
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.
Light: Morning sun; afternoon shade in hottest areas (see variety specific details, left)
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
They Start Out Looking Like This:
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