An impatient person’s guide to making black flowers

For World Goth Day, I have tried to make a black flower. It didn't work, but I have failed in a way that might explain why it's not easy to make a Rainbow Rose.

Long-time readers might be aware we talk about Rainbow Roses in the office every so often. In theory, if you split a stem in four and put each quarter stem in a dye, you should get a rainbow in the petals. Examining a Rainbow Rose made by a professional seems to confirm this, but attempts to make one have failed badly.

So over the weekend, I carried out a short experiment. I knew World Goth Day was coming up. We know black is not a common colour for flowers. So could I make a flower black?

Breeding truly black flowers is not simple. The colour of a plant depends on its pigments and structure. Plants don’t make black pigments because there’s no benefit. Talking to the Guardian, Reading’s Alistair Culham said: “Black doesn’t really help a plant to stand out.” You can breed darker and darker flowers, that add more and more pigment to the petals by artificially breeding them, and get close to black.

I had this idea a week ago, and didn’t fancy waiting a few decades to see if we could do better. Instead, I used dye and a careful choice of flower.

Roses are probably a bad choice of flower if you want a plant that will draw up dye. Growing and selling roses is a global business, so you’re unlikely to get the freshest roses for an experiment. Instead you’ll have quite woody stems. That’s why I chose carnations.

Set-up

Carnations have a green stem and should still be drawing up plenty of water when you buy them. To test if I could dye flowers, I bought six white carnations.

Flowers and test tubes
Here are the flowers, pre-experiment.

Two would be control carnations, to make sure I hadn’t bought a freak variety that mysteriously turn black. Two would sit in a test-tube of water and “Waitrose Essential Black Food Colouring” which is a liquid. If you don’t understand why black food colouring would be essential, you’re not getting into the spirit of World Goth Day. The last two would sit in Rainbow Dust Concentrated Gel dye.

Food dyes
I’m not sure how food colouring can be naturally black, but I’m not pulling on that thread today.

The idea was that using two dyes would make sure I wasn’t misled by choosing a bad dye. Using two flowers in each case meant that if I messed up cutting the stem of one flower, the other was still there in the tube. So a bad flower shouldn’t be a problem either.

The mix of liquid dye to water was about 1 in 10. For the gel, it was a 2cm squeeze. During this step, a portion of my hand turned black. If you’re doing this at home or with your own children, disposable gloves are a good idea when adding dye.

Finally, because the florist knew I was trying to make black flowers, she suggested starting from the darkest starting point I could. That’s why I also had six red carnations.

The flowers in gel dye are closest, next the flowers in liquid dye, then the controls at the back.

I then left the flowers in the conservatory.

My expectation was that the liquid dye would do best. After all the water that the stem pulls up is liquid. The only reason I tried the concentrated gel was that the florist suggested it. I was so sure that would be disappointing that I made a special trip out so I could have a liquid dye.

After half an hour the first fringes of black appeared on the petals.

Petals with very small black markings
There is black in there, but you have to look closely.

I was surprised there was something visible so quickly. I was expecting it to take a couple of hours. I was also surprised by which petals they were. These were the flowers in the gel test tube.

Results

After about ten hours the flowers were close to finished.

White carnations with black lining around the edges
Some black and white carnations. (click to enlarge)
Red carnations with black lining around the edges
Some black and red petals, if you look closely. (click to enlarge)

Here are the results after 24 hours for the white flowers.

The red flowers didn’t really open, but followed the same pattern.

One feature that doesn’t come across in these photos is the health of the stems. One sample did like it was not enjoying itself and hanging its heads low. And that was the liquid dye sample. Both white and red flowers struggled. A better experiment would change the concentration of dye to water. But given that there’s no real visible effect on the flowers from the liquid dye, it’ll have to be a more committed experimenter than me.

Not only did the dye affect the flowers, but other parts of the plant also turned darker too.

two leaves, one darker than the other
Control leaf above, gel dye leaf below

This will come as no surprise to botanists. The gel is pulled where the water goes, and the water is needed for photosynthesis. Again the lack of dying in the sample stems indicates that water was not rising through the stem.

So what have I learned?

Horticulture is hard. I knew this already, but it’s a handy reminder. No one sane could seriously expect to knock up a few black flowers on a weekend when it takes people years to breed dark varieties. If it were that simple, why would there be a viable market for dark blooms? To be honest, I’m actually surprised the white flowers looked as good as they did.

Not all dyes are equal. As this page says, food dyes are not going to work well. Likewise for home craft projects, not even all food dyes will work well. Sooner or later I will try to make a rainbow carnation and, when I do, I’ll be using food gels, not liquid dyes.

Listen to your florist. I was convinced liquid food dye would do better. I was 1000% wrong on this, as the flowers did worse than the control sample. The reason I used food gel was on the florist’s suggestion. As a means of showing how plants draw water up to their flowers, she was entirely right.

Enjoy World Goth Day, and with a little food gel you can make any day a Goth day.