Oxalis treasure or trash

I had a special treat during the past week. A regular reader of this column rang me to say she had a special present for me from her late mother's garden - a big pot filled with oxalis.

I know most of you will be appalled at the idea of such a gift, and anyone who has struggled with any of the few pestiferous members of this widespread family of bulbs will throw their hands up in horror at the thought of a gift of such pernicious, unwanted plants.

But those of you who are fans of small bulbs will have shared my excitement at the offer, especially as it was a pot of the intriguing O. versicolor, the creatively-coloured little plant with barber's pole flowers. This little charmer has a slightly different habit of growth to most species as it forms a low-growing sub-shrub with almost woody stems only a few centimetres high.

At this time of the year, their flowers are in evidence and what funny little flowers they are. The plant produces crimson-striped, funnel-shaped buds that open to pretty white cup-shaped flowers with crimson margins.

We grew this plant years ago in a warm garden in front of one of the glasshouses in the nursery, in a bed where one of our sons grew his miniature roses, and it flourished, which gives a good indication as to the sort of conditions it requires - warm soil, a sunny open site and a bit of watering over the summer.

It is reportedly half hardy but coped with anything our climate could throw at it. And it did not spread at all.

I have a bit of a thing about this group of lovely little bulbs and have several pots growing in full sun beneath my office window, many of which have been in flower over the past few weeks.

I think my favourite is the delightful South African species, O. massoniana. This is a strong growing and free-flowering form, ideally suited for growing in containers. It has the most amazingly coloured flowers - sometimes called "bright orange", but really more of a warm, light terracotta colour with bright golden centres.

Unusually for oxalis, this species can be propagated from cuttings of the tree-like shoots. I find this one is not as strong growing as some other species but is startlingly beautiful when in flower in its terracotta pot.

The various forms of O. purpurea I grow are now just slightly past their best. This is wildly variable South American species, and is grown for its attractive winter flowering habit, and their attractive cut foliage. There are several forms available here and an even wider range on sale overseas.

The one I like most is a deep purple foliaged variety I have seen described as Nigrescens. Naming of these plants can be confusing as nurseries have confused similar looking types, and it may be possible it is the same variety also known as Garnet. The deeply-coloured, clover-shaped leaves offset the glowing pink flowers wonderfully. The flowers are difficult to photograph effectively as they have a shiny gloss and always appear lighter in photographs than they do in the garden.

I grow two other forms of O. purpurea, both having (oddly enough) green leaves; one with glowing white flowers, the other with the same shining pink flowers of the dark-leaved variety. There are yellow and cream forms of this species too, but I have never seen them on offer in New Zealand.

This species increases well in the pots and, even though there are plenty of species I would happily plant in the garden, I think I would be hesitant to plant any of these varieties in light well-drained soil as they might get a little too territorially ambitious and multiply a little too quickly.

One I do not have at the moment, and must find again, is the first one I ever grew - the delightful yellow-flowered South American species, O. lobata. When I planted my first rock garden more than 30 years ago, I made a couple of clumps of this one of the highlights. This lovely little plant is doubly deciduous - it dies away in the early winter before springing into life in early summer, growing for awhile then disappearing again, only to resurrect itself to flower in late autumn. The flowers are daffodil yellow and typically cup-shaped. This is not an easy species to find but should be sought out as it is so attractive.

One I would love to track down (it is available from specialist nurseries sometimes and I have even seen it advertised on Trade Me) is a lovely light yellow variant of the golden O. compressa with double flowers. The flowers are informally double, slightly messy in fact, but they are very appealing. The single-flowered form is an attractive bright gold and is well worth growing too, if you can find it.

At the other end of the scale is the terrible Oxalis latifolia - this is one you definitely do not want. It is the persistent oxalis that nearly drives gardeners to distraction as it is so hard to control. Removing the tops has no effect, and cultivation tends to make things worse not better, as this species has lots of little bulbs that break away from the main rootstock at the slightest disturbance. There are some chemicals that can control this, but you need to leave the land fallow for awhile for it to work effectively. We have a few patches of this, which I strive to keep under control, not always successfully. I have learned, rather begrudgingly, to live with it.