It is one of the interesting things about gardening that many species we love and treasure in the garden have close relatives that are thuggish and not to be tolerated. This week I have been engaged in a deadly battle with a plant that was given to me by a friend some years ago, and unidentified member of the Polygonum family, related to the lovely ‘Painters Palette’. For nearly ten years it has been in my perennial garden, slowly increasing but this year it has had a rush of blood to the head and has decided to make a takeover bid for the whole garden, sending out envoys all over the place in an attempt to colonise any available land. I have dug most of it out, but I am not fooled – I know there will be some roots waiting a bit of rain to burst into life.
There are plenty of weeds in the family, but also a few choice garden plants, including some lovely tall perennials and some great groundcovers. I feel pretty ambivalent about them though, as I do about the feature plant this week – the spurges, the remarkable Euphorbias. When you consider that there are over 2,000 species of this cosmopolitan genus it is hardly surprising that there are some lovely charmers – and some of the most despicable thugs as well. They range from tiny ground cover plants right through to trees, and almost all have a milky, acrid sap, earning some the moniker of milk weed.
To start with the charmers – and bearing in mind that I am writing this on Waitangi Day, we have to start with the native sea spurge, Waiuatua, E. glauca. This occurs in all the major islands of New Zealand, in coastal areas, but is now very rare in the wild and regarded as an endangered species. As the Latin name suggests, this robust herbaceous plant has bluish-grey leaves in the best forms, contrasting nicely with its reddish stems. Like many coastal herbs, it spreads with underground runners, and in well tilled soil will wander about a little, but is unlikely to become a problem in most gardens. It has become a favourite with municipal gardeners who value its value as a contrast to either grassy foliage, or deeper coloured forms of flax. It will grow to about 90 cm high and is surprisingly hardy for a costal plant.
There are a couple of Euphorbias released in New Zealand over the past couple of years that you could be fooled into thinking are natives – they are called ‘Kea’ and ‘Tui’, but do not be fooled – these are alien intruders, bred in England from overseas species. They are both interesting plants for the garden, is misleadingly named. ‘Tui’ has deep purple, almost black foliage which in early spring produces flower spikes of plum to dark purple flowers. ‘Kea’ is a different bird altogether – it has a tight, compact habit with late winter flower spikes which flush pink red before opening to a mass of continuous lime gold blooms throughout spring and summer. These two varieties grow to about 60 cm high and are both reliable garden plants.
‘Kea’ is a form of Euphorbia characias as is one of the oddest of these spurges – the brightly variegated ‘Silver Swan.’ Again originating in England, this variety makes a tight mound of green and white variegated foliage. In late winter to early spring, the terminal flower spikes open to green and white variegated blooms. Like most Euphorbias, this is best grown in full sun in well drained soil to give of its best. There is similar variety hailing from Australia called ‘Tasmanian Tiger’.
The chameleon spurge, Euphorbia dulcis 'Chameleon', has leaves that open purple and deepen throughout the growing season to a rich red by the time autumn comes. Like most purple-leaved plants, it serves as an accent amidst the dominant green foliage of most gardens so place it where it will make a good contrast. Its bracts are yellow and it grows about 40 cm.