Some plant names strike fear into the heart of the experienced gardener! Mention Japanese knotweed, ground elder or bindweed to anyone that has had to suffer these weeds and they are likely to need a sit down. And some garden plants provoke similar reactions. One of these is oxalis.
There are hundreds of kinds of oxalis, from all over the world and for gardeners they vary from beautiful, delicate alpines to rampageous weeds. In warmer climates the ‘Bermuda buttercup’ (Oxalis pes-caprae) is a terrible, winter-blooming weed (in the Northern Hemisphere). In our own gardens Oxalis corniculatus, introduced as an ornamental plant, is a horrible, though pretty, weed. It creeps and roots over the soil with pretty, shamrock leaves, tinted purple in the sun, and the yellow flowers are followed by seed pods that twist and fling seeds many metres. The other common oxalis is the summer flowering, pink Oxalis floribunda. It is not usually a pest but it is almost impossible to dig out because it produces ‘trillions’ of tiny bulbils that drop off when you dig it up!
We do have native oxalis and the prettiest is wood sorrel (Oxalis acetosella) which is a lovely woodland plant. The name ‘sorrel’ is from the taste of the leaves which taste of sorrel. Both plants contain oxalic acid which is edible in small quantities and give both plants their citrus, zingy taste.
But oxalis are a mixed bunch and in recent years one species has attracted lots of attention because it is a lovely windowsill plant. The names of many oxalis are confused and it can be difficult to to know what you have. Because the leaves are in three parts, they are often called ‘false shamrocks’. I will call this Oxalis triangularis, although it is also called Oxalis papilionacea. It is native to South America. You can buy it as a pot plant or as dry rhizomes (scaly, thick roots). The most common forms have gorgeous purple leaves, often with a paler triangle in the centre and pink flowers.
On the windowsill it will retain its leaves all year but it can also be dried off in winter and the rhizomes repotted in spring. So do not panic if your plant dies down if it is dry – it should recover. I think it is one of the most useful plants I grow.
Although frost will kill the foliage and intense cold, if it freezes the roots, will kill the rhizomes, it often survives winter in mild areas. It does in my garden. In the home it needs a bright windowsill but outside in summer it thrives in sun or part shade. I use it in so many ways in my garden especially in patio pots in summer. It is also great in hanging baskets and as an edger in borders. If you lift the rhizomes in autumn and keep them dry and free of frost (like dahlias – but much smaller) they can be replanted the next spring and one potful will become dozens of rhizomes in a season.
There are lots of varieties of this useful and easy plant and, to be honest, most are very similar. But one is very distinctive. Called ‘Irish Mist’, it has green leaves (flushed purple underneath in strong sun) irregularly flecked with silver. The flower are the palest possible pink. Like its purple-leaved brothers, the flowers are very popular with bumblebees so wildlife will love them as much as you.
The only problem I have found with these plants, and it tends to be the purple-leaved forms rather than ‘Irish Mist’, is that rust disease can damage the leaves in wet summers. It will not affect plants in the home and new foliage quickly springs up on plants in the garden, but I must just mention it!
If you are a keen cook, you will be pleased to know that the leaves and flowers are edible. Watch any TV chef and they will take their tweezers and arrange a few oxalis flowers on their plate and charge you another £5.
Take another look at this adaptable and exciting plant. You will probably have to look in the houseplant section at Knights to get a plant but be assured it will thrive outside on your patio and become one of your summer favourites.
Weekly reminders
Keep picking sweet peas as they open. If seed pods are allowed to form the plants will stop blooming.
There is still time to sow lots of veg. Sow peas, beans, lettuce, kale and annual herbs like coriander.
Plant out Brussel sprouts, kale and leeks
Feed your onions to stimulate growth and help the bulbs to swell next month
Now the weather is a bit wetter, make sure you protect vulnerable plants like dahlias from snails
Net strawberries and other fruits to stop bird stealing them all.