Ultraviolet extends far beyond marketers’ on-trend colour selection
Purple plants — with a hue sometimes invisible to the eye — can be good for health
Each year, one colour is designated as the “in” colour, encompassing everything from paint to fashion, and even gardens. This year, the hot colour is ultraviolet.
Now as my family and friends can attest, I’m not much of a trendsetter (nor a trend follower, for that matter) but I’ve always loved ultraviolet-coloured plants. Ultraviolet plants look terrific all on their own, or a favourite of mine is to match them with yellow flowers.
But being the kind of guy who loves plant science, ultraviolet reigns supreme for me for reasons beyond pure esthetics. Ultraviolet light is both a friend and enemy of plants, and it has a profound effect on how plants both grow and survive.
A BIT OF SCIENCE
The sun is our source of ultraviolet light, which can be further subdivided into three spectra — A, B and C.
Ultraviolet C is the really bad one. It is highly energetic and damaging to all living things, but thankfully it is intercepted and absorbed by our earth’s ozone layer. Ultraviolet B is less energetic than ultraviolet C, but can still cause some damage to living things, while ultraviolet A has the least amount of energy.
Plants really hate any ultraviolet light. It damages their sensitive chlorophyll — the stuff that plants use to capture ‘good’ sunlight — and since plants can’t run away from ultraviolet light they must stand and fight. For plants, the solution to the ultraviolet dilemma is to synthesize chemicals that allow most of the usable sunlight into their leaves, while also blocking a lot of the ultraviolet light.
One major category of these protective chemicals is called anthocyanin. It provides some plants with a characteristic purple coloration while, concurrently, “deactivating ” damaging ultraviolet light. Anthocyanin is not just great for plants, it’s also great for people who eat anthocyanin-rich plants because it is also a powerful antioxidant that scrubs some of the bad stuff from our bodies.
Anthocyanins are common in plants like purple cabbage, purple cauliflower, blueberries and black currants, to name a few. The leaves of some trees and shrubs contain anthocyanins, revealing them in the fall as chlorophyll is lost.
Bees are particularly attuned to ultraviolet light. Some common plants like marsh marigold produce ultraviolet-sensitive patterns on their flowers specifically to attract bees for pollination. Humans are blind to the purple hue of marsh marigold flowers, but bees can see a pattern called bees purple in the centre of the flower that looks to them just like a big purple welcome mat.
Ultraviolet light not only provides beauty, nutrition, and bee landing pads, but it can kill a serious plant disease called powdery mildew. Many gardeners are familiar with powdery mildew because it attacks a wide range of plants, leaving a white, powdery residue on leaves and flowers. Mildew loves the shade because trees, shrubs and buildings block a lot of the fungi-killing ultraviolet light.
WHAT SHOULD YOU DO?
If you are looking for ornamental plants that have purple or ultraviolet-coloured flowers and foliage there is a very long list to choose from in every category, from annuals and perennials to trees and shrubs.
But I think it’s the purplecoloured vegetables that are my favourite, because they not only look cool but they are also tasty and produce anthocyanins that are great for human health. Here is a short list of a few great ultraviolet vegetables that grow well in our region:
Graffiti cauliflower – Intensely purple curd (head) and looks stunning served raw or on a veggie platter
Calibos cabbage – Large pointed, purple heads and dense interior with a small core
Purple Mist snow peas – Dutch heirloom pea that can also serve as a striking tall ornamental
Scarlet Kale – Highly curled leaves and a true super food
Royal Burgundy Beans – Crisp and meaty with long (15-centimetre) pods
Purple Haze Carrots – Deep purple on the outside, bright orange on the inside
So whether you choose to go the ornamental route, the edible route, or both, there is no shortage of ultraviolet plants to suit your fancy. But just remember to wear your sunscreen when working in the garden. Plants have figured out how to deal with ultraviolet light, we humans are still learning.