Update:
The weather has turned so I have taken both sample skeins out of the dye. The results are shown below.
Original post
My lovely husband gave me roses a week ago, but sadly they have drooped and begun to drop petals. I’ve decided to use the petals for dyeing; they were a lovely dark red and I hope I’ll get at least a pale pinky-brown from them.
The main thing I have learned is not to overheat petals – or any red natural dyes for that matter – as that seems to make them brown.
I tore up the petals and covered them in cold water, then added a little salt and white vinegar to the pot before gently heating it to below a simmer. I left the petals overnight to steep and strained the liquid off this morning. After that I put the drained petals into a muslin bag, returned this to the pan and added a skein of wet mordanted yarn to the cold liquid before reheating to a mid range temperature.
After heating the dye I poured the contents of the pan into a large lidded jar and have left it to steep for as long as it needs…
I’ve also put some over-ripe strawberries into a solar-dyeing jar next to the rose petals.
Vikki Haffenden 
Beautiful color