Tag Archives: ornamental oxalis

The ornamental oxalis

The white form of Oxalis purpurea – the best of them all

Back in our nursery days, we had a large range of ornamental oxalis. I see in our old mailorder catalogues that we offered over 20 different varieties that we had in production at the time and I wrote extolling their autumn merits for several publications.

Twenty years on and the oxalis collection has refined itself down. It is the difference between gardening in containers and gardening in the soil. Some of those varieties were so delicate and touchy that we have lost them. Others needed to be kept confined because of their invasive proclivities. Some flowered prettily enough but their season was so short that it was hard to justify their place in the garden. I decided years ago that I was not going to fluff around with plants in containers. We have quite enough garden with many different micro-climates. If plants couldn’t perform in the garden, I didn’t have the time or inclination to nurture them in controlled conditions in containers.

These days, the oxalis we still have are the stand-out performers (and a few of the nasty weed ones that most of us battle – particularly the creeping weed which I think is Oxalis corniculata). The star has always been and still is the beautiful, well-behaved Oxalis purpurea alba. Large white flowers in abundance over a long period of time and not invasive. At this time of the year, I am more than happy to use it as ground cover in sunny positions. Oxalis flowers don’t open without the sun so they need to be in open conditions.

Oxalis purpurea nigrescens

O. purpurea is a variable species. The striking red-leafed form (O. purpurea nigrescens) with pink flowers comes a bit later and is invasive so needs to be kept confined. We also have a strong-growing (somewhat invasive) green-leafed form with very large pink flowers which is worth keeping and also has a long flowering season. Back in the days, I recall more than one person telling me that there was a red leafed form with the large white flowers but I have never seen it so I rather doubt its existence.

Oxalis luteola as runner-up in my best garden oxalis list

The standout yellow is Oxalis luteola. It, too, is well behaved and forms a gentle, non-invasive mat that flowers for a long time in mid- autumn, combining well without competing with other bulbs like the dwarf narcissi that are in growth but won’t flower until late winter and early spring. It leaves the rabbit-ear Oxalis fabaefolia in the dust for length of flowering time. Both have large, showy yellow flowers but the latter’s flowering time can be measured in days rather than weeks.

Oxalis massoniana

I am very fond of little Oxalis massoniana with its dainty apricot and yellow blooms but it needs a bit of nurturing to keep it going. The popular old candy-stripe O. versicolour is happy left to its own devices in the rockery but will not come into its season for a few weeks yet. It is the only one I know that looks more interesting when its flowers aren’t open because the striped buds disappear into a fairly ordinary white flower on sunny days.

I have hung onto the strong-growing O.eckloniana for its large lilac blooms but I keep it confined to a shallow pot sunk into the rockery. I could rustle up a few of the others from around the garden, like O.hirta in both lavender and pink, O. bowiei, O, lobata, the unusual double form of O. peduncularis  and O.polyphylla but they are not the star performers that luteola  and purpurea alba both are.

If you are into container gardening, a collection of different ornamental oxalis species give interest on a sunny terrace or door step from autumn to mid-winter. I saw somebody listing a whole range of different oxalis on Trade Me at one stage. In fact, it looked like somebody had bought our full collection all those years ago and kept it going so they are still around. If somebody offers you O. purpurea alba or O. luteola, don’t reject them just because they are oxalis. They are worth having.

Oh look! Here is a little display board I prepared earlier of under half of the oxalis that we used to grow

In praise of ornamental oxalis (or wood sorrel, if you prefer)

Oxalis show considerable variation in leaf form (and in flower colour)

Oxalis show considerable variation in leaf form (and in flower colour)

Most people shudder at the mere mention of oxalis. The bad reputation of a few has tarnished the entire population. We would not be without the cheerful sight of them blooming from early autumn through winter, but the most common reaction from others is complete dismissal. I have even resorted to their colloquial name overseas – wood sorrel. It sounds so much prettier and more acceptable than oxalis.

Over the years, we have gathered up around 30 different ornamental varieties but these are a mere drop in the bucket. The oxalis family is huge. In the wild, the number of different species is into the late hundreds. That is not to say that they are all of great merit. Nor are they all bulbs. Equally, not all are invasive.

O. deppei "Iron Cross" grows and flowers in the opposite seasons to most ornamental varieties

O. deppei "Iron Cross" grows and flowers in the opposite seasons to most ornamental varieties

Most oxalis are native to either South Africa or South America, though it is the former that gives us the majority of varieties which have garden merit. Most are triggered into growth by late summer rain, so they come into flower around this time of year. The two notable exceptions we have in our collection are both from South America. Oxalis deppei “Iron Cross” (named for the markings on its leaves) is from Mexico and going dormant now, to return to growth at the start of November. O. triangularis, with its triangle shaped leaves in deep burgundy, is Brazilian and also flowers in summer. I bought this one at a car boot sale where I commented that it was an oxalis that I did not have. “No,” protested the vendors. “It is not an oxalis. It is a triangularus.” I didn’t argue.

Some of these oxalis are perfectly safe in the garden. I can vouch for this after decades of growing them in the rockery where they have never threatened to become a weed. Others are downright dangerous. Turn your back and they will invade at alarming speed. Such wayward habits don’t mean you have to shun them. Keep them in pots. You can either plunge the pot into the garden (which reduces the need to water it), or have a collection on a sunny doorstep. Oxalis only open their flowers in the sunshine. When they have ceased being attractive, you can move the pots out of sight for the rest of the year. We have not had problems with them setting seed so as long as the bulbs are confined, they rarely escape.

My all time favourite - O. purpurea alba

My all time favourite - O. purpurea alba

Same species but different form and very different behaviour. Keep O. purpurea "Nigrescens" confined to a pot

Same species but different form and very different behaviour. Keep O. purpurea "Nigrescens" confined to a pot

My all time favourite is the pristine white O. purpurea alba. It has an exceptionally long flowering season and is extremely well behaved in the garden. A mat of this plant opening up its large blooms to the sunshine is a delightful sight. Each flower has a golden eye. Purpurea is a variable species. The green form (same clover-like leaves but with large pink flowers) also has an excellent length of flowering but I haven’t had it long enough to know whether it is garden safe or not so I still keep it in pots. The reason for my caution is that O. purpurea ‘Nigrescens’, highly desirable for its deep burgundy foliage and big pink flowers, is dangerous. I have seen it invade an Auckland garden on heavy clay. It was as bad as the weedy varieties, just more ornamental. Keep it confined at all times.

My second place favourite is the lavender O. hirta. We also have a bright pink form of it, but the pastel lavender is prettier. This has very different foliage – trailing clusters of leaves. The range in leaf form is surprising. O. fabaefolia is often called the rabbits’ ear oxalis because its leaves look like pointed rabbits’ ears. It has a big yellow flower but a very short season.

O. luteola - an excellent garden variety

O. luteola - an excellent garden variety

Oxalis luteola, with its neat mat of clover-like leaves and masses of sunshine yellow blooms over many weeks, is another tried and true garden plant here. It has never been a problem in the rockery and gently grows amid other plants without ranging far afield. O. lobata is like a miniature form of O. luteola and equally garden safe.

Oxalis flower in colours from white, through the full gamut of pinks and lavenders to the crimson red of O. braziliensis, yellow, and apricot-orange tones. The well known O. versicolour has a pointed bud which is candy striped pink and white, like a traditional barber’s pole, though in the sun the flowers open to white. It is the only one I know which is showier when it is not open.
Oxalis (or wood sorrel, if that sounds better) are easy and fun to grow for a bit of cheer as the autumn draws in.

We keep O. eckloniana in a pot plunged into the garden

We keep O. eckloniana in a pot plunged into the garden

Growing oxalis in containers:

If in doubt, keep oxalis confined to pots in sunny positions.
• Pots can be plunged in the garden to reduce watering.
• Repot every year or two.
• Empty the pot onto newspaper and choose only the best looking bulbs. You will see which varieties have dangerous tendencies – either masses of tiny bulbs or long runners with too many bulbils attached. Throw the rest out with household rubbish to prevent any escaping.
• Free draining potting mix is recommended.
• If you have used a commercial potting mix, it will have fertiliser already added. If you are not repotting every year, the time to feed is as the bulbs are coming in to growth.
• Wide, shallow pots give the best display.
• Keep pots dry when bulbs are dormant to stop them from rotting out.

Perfect for sunny doorsteps

Perfect for sunny doorsteps

Dealing to the weedy ones:

There are no easy answers when it comes to getting rid of the weedy oxalis in gardens and lawns. O. corniculata is a creeping plant which doesn’t have a bulb so it can be weeded out. It spreads rapidly from seed and matures quickly so it pays to be vigilant and to dispose of plants in the household rubbish to avoid dispersing the seed. It can be green or red-brown in leaf and has tiny yellow flowers.
The pink or yellow flowered weedy bulb forms are more problematic, especially if they are growing through other plants. Glyphosate will kill them eventually, if you keep applying it every time you see leaves reappearing. I have never tried Death to Oxalis but it appears to need frequent reapplications as well. If you can lift all the other plants out of the garden border, you can sieve the soil or even replace it all. If you cover the area in black plastic and let it bake throughout a hot summer, it will sterilise the soil to some extent. Failing that, you just have to be persistent and vigilant, getting rid of every little bit you see.
First published in the Weekend Gardener and reproduced here with their permission.

O.hirta lavender - second place favourite

O.hirta lavender - second place favourite


O.massoniana - massed in a wide, shallow container in full sun

O.massoniana - massed in a wide, shallow container in full sun


O. polyphylla shows very different foliage

O. polyphylla shows very different foliage


O. bowiei - bold and showy very early in the season

O. bowiei - bold and showy very early in the season

Plant Collector – Oxalis massoniana

Oxalis massoniana

Oxalis massoniana

Envy the gardener who has not had to battle invasive oxalis. Most of us know only too well how difficult it is to eradicate the weedy ones. But there are only a few villains in a very large family and unfortunately, most people shun the lot because of those few. We wouldn’t be without the decorative oxalis and O. massoniana is just one putting on a splendid display at this time.

I think we must have around 30 different oxalis in pots and in the garden here and they are just a drop in the bucket of the many hundreds of different species. Flower colour ranges from white, through the gamut of pinks, lilacs and lavenders, crimson red, yellows and oranges. The foliage is also varied from the clover type leaves to fine and feathery, trailing and even miniature palm leaves. We must have them flowering for six to eight months of the year. I should comment that some have a flowering season lasting a long time, while others are a bit of a flash in the pan.

Some oxalis are garden safe but if in doubt, keep them in pots where they are wonderfully forgiving of benign neglect. The flowers only open in the sun so the pots make a lovely seasonal feature on a sunny doorstep. I have tried massoniana in the garden but it seems to be happier and showier in a big, shallow container.

The apricot and soft yellow two-tone colouring is very pretty and the flowering season lasts a good length of time. As with most of the autumn and early winter flowering oxalis, it is native to the bulb wonderland of South Africa. If you can’t bear the thought of growing oxalis, just call it by its more romantic sounding common name overseas – wood sorrel.

First published in the Waikato Times and reprinted here with their permission.

Tikorangi Diary: March 30, 2012

The lovely autumn oxalis - O.eckloniana

The lovely autumn oxalis - O.eckloniana

Latest posts:

1) Lycoris aurea – the golden spider lily
2) I guess it was inevitable that the thoughts here would be directed to trees after the casualties of last week. We accord them a rather higher value than many New Zealanders who see them as a disposable commodity. Abbie’s column.
3) Grow it yourself: rocket. Merely a humble, quick growing brassica that has been elevated beyond its status in the lexicon of vegetables.
4) In the garden this fortnight and the talk is about sustainability and our guilt over the use of motorised equipment.

The clean up continues

The clean up continues

... and Oxalis massoniana

... and Oxalis massoniana

Tikorangi Diary

A magic week of weather has seen first Mark and then Lloyd out cleaning up the fallen totara and Picea omorika. It is done. I rather liked the piles of sawdust like a zebra crossing where the ramrod straight trunk of the picea was cut for firewood. While it looked wonderfully straight, the wood lacked heart and was pretty soft.

The pretty ornamental oxalis are all coming on stream. I used to pot some of each to sell but finally figured that too few people shared my pleasure in these autumn bulbs so it was a waste of time potting them. These days we just enjoy them ourselves. The nerines are starting but won’t peak for another week or two.

Tikorangi Notes: May 14, 2010

Maybe best not to follow Mark's example
Latest posts:
1) May 14, 2010: The lovely blue of autumn flowering Moraea polystachya keep continuing over a long period.

2)May 14, 2010: Outdoor Classroom – our fortnightly step by step guide. This time it is pruning a rampant climbing jasmine which is blocking most light in a window as well as threatening the downpipe, roof spouting and even the roof tiles. We used to have a member of staff who refused to use any of our ladders on the grounds they were unsafe. Mark has no such qualms as can be seen in this photo which we did not dare to use in this Outdoor Classroom instalment which gets published in our local paper. We could see an onslaught of outraged letters to the editor about unsafe practices and that would be from people who didn’t even know that the ladder in question lacks even a bracing cross bar. Mark credits regular yoga for his good sense of balance.

3) May 14, 2010: As our unusually calm, dry and sunny autumn continues, there is plenty to do in the garden this week. Advice on lawn care, harvests, green crops (yet again) and more.

The colours of the autumn flowering oxalis

4) May 14, 2010: After the breathtaking inadequacies of the Tui NZ Fruit Garden, it was a relief this week to be reviewing a NZ publication of merit. Threatened Plants of New Zealand deserves a place on the shelf of anybody interested in our native flora, botany or conservation. Apparently 1 in 13 of our native plants are currently under threat of extinction.

5) May 14, 2010: The first of a new series of notes about plants which are tried and true in our garden – this week the smaller flowered vireya rhododendron hybrids.

6) Camellia Diary instalment number 2. It appears to have been a busy week for me with new posts!

Oxalis purpurea alba - one of the very best garden varieties.

Last week certainly ended on an exciting note with my review of the new Tui NZ Fruit Garden Book by Sally Cameron (published by Penguin) even making the metropolitan daily papers and being picked up by radio as well as other publications. The speed with which the internet disseminates information is amazing, nearly matched by the speed at which Penguin ordered a total recall of a book they had only released days earlier!

This week it is back into the garden. Mark has been continuing his autumn harvesting routines though he had the grace to laugh at his banana harvest which will be revealed in detail in due course. I have to say we are more than marginal for growing bananas and he has to work hard to get a crop from his outdoor plants. In the garden, the ornamental oxalis are making a very pretty picture indeed. I think we must have somewhere around 30 different varieties now across a range of colours. These are surely an under-rated autumn bulb in our New Zealand gardens.