flower colour

Nature and Nurture: the Colours of Hydrangea

These are blooms of Hydrangea macrophylla normalis, otherwise known as lacecap hydrangea.

Pink lacecap hydrangea, grown from cutting in pot July 2021

The pink one is a clone of the blue one, grown from a cutting. The difference is that the plant with blue flowers is growing in the natural soil in my garden (supplemented with compost, fertilizer, and lots of water), while the pink one lives in a pot. The soil in the pot is a blend of natural soil, compost, various supplements, and lime. It may have been left over from the mix I put together for tomato plants the year I potted up the hydrangea cutting. The key difference is lime. I add extra lime to tomato soil to avoid so-called blossom end rot in the tomatoes. It’s caused by calcium deficiency, hence the need for lime.

According to Wikipedia, “An acidic soil (pH below 7) will usually produce flower color closer to blue, whereas an alkaline soil (pH above 7) will produce flowers more pink. This is caused by a color change of the flower pigments in the presence of aluminum ions which can be taken up into hyperaccumulating plants.”

Either way, hydrangeas perk up the garden, which starts to look tired by July. The flowers last for weeks, and even retain “interest” into the winter (meaning they hang on in a discoloured state, which may be somewhat interesting). I admit I prefer the blue colour, which is why I go out of my way to supply water to the plant starting in June, because it would bloom poorly or not at all otherwise. But seeing the pink flowers on the potted cutting-grown plant (which bloomed for the first time this year) has been a nice demonstration of nature and nurture.

This Was May…

Before May of 2020 fades into memory, here are a few memorable images from my garden, along with a thought or two.

As a new gardener, I read a lot of books and articles about garden design that suggested using plants as an artist uses pigments to create stunning colour combinations. In fact, I recall the term “plant palette” being tossed around. After years of striving to do this in reality, I’ve decided it’s not a realistic goal, outside of “great gardens” with staffs and resources. For the small gardener, failure and fits (apoplectic and otherwise) are guaranteed. Plants aren’t pigments. They won’t all bloom at the intended times. A key component of the design will die or rampage through the planting. Something else will creep in and introduce a clashing colour. But delightful conjunctions do happen. My best combinations are happy accidents, not carefully selected groupings. The thing is to see and appreciate them when they happen.

The header image shows a happy combination of Siberian irises (finally blooming well here), with orange poppies (Papaver rupifragum) and the white flowers of Libertia grandiflora in the background. I planted the Libertia a couple of years ago. It didn’t bloom last summer, so I was beginning to think the conditions here didn’t suit it (it’s a New Zealand native), but it’s performing beautifully this year.

Orange poppy, Papaver rupifragum — It would be tempting to use flowers like this as pigments. *Papaver rupifragum*, otherwise known as Spanish, Moroccan, or Atlas poppy, looks great against the grey foliage of *Senecio* “Sunshine.”

While “painting” with flower colours is a dubious proposition, it is possible to create effects of contrasting and harmonizing forms and colours with foliage. Leaves, after all, are present throughout the growing season, whereas flowers are fleeting whims.

Foliage: hellebore, hosta, variegated grass, and Chinese witch hazel, May 2020 — A happy combination of leaves: Chinese witch hazel (*Hamamelis*) at the top, with hellebore, variegated grass, and hosta below.

Japanese painted fern in Chinese jar, May 2020 — And then there’s this fern — Japanese painted fern (*Athyrium niponicum*). It’s a colour combination in itself, with shades of greenish grey, silver, and maroon.

Creamy yellow rose — A rose is perfect on its own. I have no idea what this one’s variety name is. I grew it from a cutting, so it’s on its own roots, not grafted. It’s blooming well this year, wafting fragrance all over the front garden.

The garden and environs are home to a number of wild creatures. Birds are the most numerous. I’ve come to recognize quite a few different ones since I began hanging up feeders in 2015. A couple of days ago, I saw a family of red-breasted nuthatches near the pond, and the following morning there was a family of Bewick’s wrens in the lilac bush. Sadly, I think one of the nuthatches is no more; today I found clusters of small grey feathers that match one of that species’ colours. I have seen Cooper’s hawks here from time to time, and I know they prey on small birds. So do crows, for that matter; I’ve noticed one visiting the bird bath recently.

Buck visiting the garden next door, May 2020 — This guy was one of a group of four (a mini-herd!) visiting the garden next to mine. (Photo is blurry because I took it through the potting shed’s window.)

Slime mold on compost pile, May 2020 — A rather bizarre “visitor” came after rain in mid-May — a slime mold that showed up on top of the compost pile. This one might be the type known as “dog vomit” slime mold. My first thought when I saw it was “Who puked on the compost?”

May really is this garden’s best month. June also, if there’s enough rain. By July, grass starts to brown off and the spring bloomers get that tired look. Of course, there are the drought-tolerant stalwarts, the “tough plants” I’ve mentioned in quite a few posts. And the gardener (that’s me) racing around frantically with watering cans and hoses, ministering to plants that aren’t so tough.

Foxglove Falsehood

I know I read somewhere that the flower colour of a foxglove (Digitalis purpurea) plant can be predicted by the colour of the leaf stems (petioles). Foxgloves are biennials; they flower in their second year of life, and then they die. Their normal flower colour is a reddish purple. It’s fairly attractive, but not nearly as elegant as the white form. Fussy gardeners who prefer the white form would therefore want to know which of a batch of seedlings would be likely to produce white flowers the following year.

If the leaf stem shows purple, I understood, the flowers will be purple. Plants with pale green leaf stems are more likely to produce white flowers. Going by this, I picked out a number of seedlings several years ago and planted them around the place. A few of them did turn out to have white flowers, but not all. Some produced blooms of a pale, washed-out pink with nothing to recommend it, and some were just the ordinary purple shade.

After this experience, I didn’t bother with systematic seedling selection. I simply let a few plants produce seed, and left a few of the resulting seedlings where they came up, in spots where a foxglove would be an asset to the scene.

Right now, I have two foxgloves with white flowers. The biggest and most impressive one has dark purple leaf stems. So does the smaller one.

Clearly, the idea that leaf stem colour predicts flower colour is dead wrong.

Just for fun, I checked the leaf stems of a rather impressive purple foxglove also in bloom now.

Its leaf stems have only a slight tinge of purple. If I had looked at them before the plant bloomed, I would very likely have predicted pale or maybe even white flowers.

So much for that notion. Consulting that fount of info, Wikipedia, I find this in the article on Digitalis purpurea:

The colours of the petals of the Digitalis purpurea are known to be determined by at least three genes that interact with each other.^[6]

The M gene determined the production of a purple pigment, a type of antocianin. The m gene does not produce this pigment. The D gene is an enhances of the M gene, and leads it to produce a big amount of the pigment. The d gene does not enhance the M gene, and only a small amount of pigment is produced. Lastly, the W gene makes the pigment be deposited only in some spots, while the w gene allows the pigment to be spread all over the flower.

This combination leads to four phenotypes:

M/_; W/_; _/_ = a white flower with purple spots;
m/m; _/_; _/_ = an albino flower with yellow spots;
M/_; w/w; d/d = a light purple flower;
M/_; w/w; D/_ = a dark purple flower.

If I could understand the above and make practical use of it, I might be able to predict flower colour in foxglove seedlings. I’d probably get more white flowered plants from my self-sown foxgloves if I pulled up any purple types before they reached full bloom, so as to keep their pollen out of circulation. But I am constitutionally incapable of pulling up (i.e., killing) any plant that is vigorously growing and about to bloom. I even have trouble dispatching certain weeds. So I’m not likely to go around “roguing out” any purple flowered plants if they look good.

In the meantime, I’ll enjoy the blooms I have, and let the white one (which, according to the above, is the white with purple spots phenotype) produce seed. Foxgloves seed like crazy. I’ll harvest a small quantity of seed and sprinkle it around the garden, and in 2019 I’ll see the results.

Update: another, rather small, foxglove plant has since bloomed with white flowers. These are pure white, and without spots of any kind. And the leaf stems are very pale green, without a trace of purple. So now I’m wondering if the leaf stem colour is somehow linked to the colour of the spots within the flower. Observing stuff like this makes gardening — even with common plants — interesting.