Why do my Cauliflower turn purple

Purple Cauliflower.  Click on the image to see a slideshow of this week's Purple spec. load.

I was sent this pic through the week with the enquiry: "Why are my Cauliflowers turning purple?"
I don't have personal experience of this issue but Mark with many years of experience in the UK vegetable industry was not surprised to see some purple discolouration. Having done a little reading (none of it scientific) Cauliflower is naturally coloured, it's through selection and breeding that white "curds" have been developed. When the plant is stressed some varieties will revert to their original colours.  From my point of view this is a perfectly handsome Cauliflower and I think the colouring will "cook out", it is certainly still perfectly edible. Growers recommend folding and pegging leaves over the curds to create a protective scarf to prevent sun scald & frost burn, I don't know if this will affect curds reverting to purple.

While we were discussing Caulis Mark used the term "Buttoning".  I hadn't heard of buttoning previously but a quick search indicates that buttoning describes exactly the problem reported earlier this year by another frustrated grower of Cauliflower Baby White. Buttoning describes Caulis or Broccoli that prematurely set heads that remain seriously undersized. It turns out that buttoning is another stress reaction by the plant. This response can be caused by any number of stresses: too wet, too dry, too hot, too cold, hungry, too many weeds, etc. Mark has also experienced Baby White Caulis buttoning in his home garden so it may be it is a variety that is particularly susceptible, which is disappointing because it is quite an expensive hybrid. Mini or Baby Cauliflower were bred specifically for the restaurant trade to produce single serve Cauliflowers, but the buttoned heads are just no value to anyone.


"Buttoned" Cauliflower also showing signs of hosting caterpillars and possibly Downy Mildew on the yellow lower leaf.

Cauliflower at a glance
Position.  Full sun
Soil. Prepare thoroughly, add organic fertilizer generously.  Caulis prefer a neutral pH so they they will appreciate some lime, especially if the soil is regularly used for vegie gardening.
Visitors.  Look out for Cabbage White Butterfly, especially in warm conditions. During cooler months watch for Aphids.
Plant selection. Tough older plants will usually respond well to moving into fresh soil or potting mix but don't try transplanting plants that already show signs of setting their curds... it's too late. A few chewed holes is not something to be frightened of, check for grubs & feed them to the chooks.  Pale yellow leaves with dark furry growth on the underside of the leaves indicates Downey Mildew, this is mostly a problem for young seedlings. Planted into ideal conditions Cualis will outgrow the problem but badly infested seedlings planted into less than ideal conditions will struggle.
Always check for healthy root growth.
Fun Fact: "Colli Flowers" were planted at Norflolk Island in March 1788.