Tag Archives: Oxalis luteola

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

Rock on – our rockery in autumn

Nerine sarniensis hybrids blooming in the rockery

Nerine sarniensis hybrids blooming in the rockery

When I am old and maybe decrepit, needing to draw in the boundaries of the garden, I shall fluff around in the rockery. I really enjoy this area and, as we enter autumn, my heart sings with the new season blooms.

Traditionally, rockeries are for growing alpines and sometimes retaining banks. However, we can’t grow alpines in our climate and our rockery is on the flat. It is pure 1950s vintage, built from a combination of rocks of various sizes, concrete and some brick, with sunken paths and raised beds divided into many hundreds of little pockets of soil. It is designed for highly detailed gardening and at about 20 metres by 10 metres, it is relatively large.

The purpose of the multitude of small beds is to keep bulbs separate and to confine the more invasive ones. Most of the pockets have two or three different types of bulbs in them to give seasonal interest.

There is always something to see, though summer is the toughest season. Because there is so much stone and the beds are elevated, parts of it dry out almost to dust. We have dwarf conifers, cycads, and a few other small shrubs to give both all year round structure and summer shade. There are a few smaller perennials and a limited range of annuals and biennials but generally, the rockery is about the bulb collection.

The range of nerine colours at one time

The range of nerine colours at one time

As we enter autumn, it is as if the rockery heaves a sigh of relief and leaps back into life. All the bulbs whose growth is triggered by autumn rains start to move.

As a general rule, we find that the species bulbs look better. They are usually smaller flowered and more delicate in appearance than the showy hybrids which can look out of scale and even vulgar in this particular context. The exception is the nerines which peak this month. While we grow some nerine species, it is the sarniensis hybrids that dominate. A few of these are of Exbury origin but most are the result of breeding efforts by both Felix and Mark Jury. The colour range is delightful – from white, through every shade of pink including near iridescent highlighter pink, to purple, corals, almost apricot, oranges and reds. Unlike the floristry business, we want shorter, squatter stems so that the heavy heads are held upright even through autumnal weather.

Cyclamen hederafolium

Cyclamen hederafolium

Also lighting up the autumn is Cyclamen hederafolium (formerly known as C. neapolitanum) which hails from southern Europe and Turkey. This is the easiest of the dainty species cyclamen to grow and it has gently naturalised itself here. It throws its first brave flowers up in January but peaks this month. It is one of a number of autumn bulbs that bloom first before the leaves appear. Others are most of the nerines, colchicums and Haemanthus coccineus.

Moraea polystachya

Moraea polystachya

The pretty autumn flowering peacock iris, Moraea polystachya, outdoes almost every other bulb with its long flowering season. It seeds down gently into the cracks between the rocks without becoming an invasive menace. Some of the ornamental oxalis also give extended displays of colour but not all oxalis are born equal and neither are they all born with good manners. The most reliable performers in our rockery are O. purpurea ‘Alba’, O. luteola and O. lobata. They have been here for decades and never looked threatening.

O. luteola and purpurea 'Alba'

O. luteola and purpurea ‘Alba’

Colchicum autumnale

Colchicum autumnale

Then there are the bulbs with a much shorter season. Colchicum autumnale makes a bold statement with its big lilac chalices held above bare soil. Hippeastrum bifida is a transient delight for us. We have it in both pink and red and the blooms look as if they have been touched with gold leaf when the sun shines through. The autumn flowering leucojum is one of the daintiest and prettiest of tiny blooms and the crocus also delight.

Autumn crocus (species unknown) with cyclamen hederafolium

Autumn crocus (species unknown) with cyclamen hederafolium

The rockery is not what I would call low maintenance. The more time I put into it, the better it looks. In spring I completely replaced the soil in maybe a dozen pockets in my efforts to eradicate the pretty but invasive Geissorhiza aspera. I do not lie when I tell you that we have battling it for well over 25 years, hence my extreme action in replacing the soil in the worst affected areas. We have to be vigilant on weeds, slugs, snails, narcissi fly and weevils. I wire brush the rocks from time to time to stop the moss growth from hiding their shapes. There is plenty there to keep me busy in my dotage and, with the raised beds, I can do a lot of it sitting on a stool. Sometimes it is the detail and the little pictures in the garden that delight.

024First published in the NZ Gardener April edition and reprinted here with their permission. 

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