This is how you know it's time to weed them out: instead of being a mass of blue flowers, they are a haze of dusty grey, often with an under-layer of unattractive black foliage.
The seeds stick to everything - the backs of my gloves, for a start.
...and to my socks...to the laces, to my tee-shirt, my shorts, to everything!
It's a horrible job, but well worth doing: clearing out all the dying plants removes a lot of slug and snail running buffet material: it allows the birds to get in amongst the plants again, so they can pick off pests: it allows good airflow among the other plants in the area, thus reducing the risk of mildew etc: and it makes the whole bed look so much better!
Don't worry about losing the plants, by the way: Forget-me-not are annual plants, so once they have finished flowering they will die anyway.
But they shed thousands of seeds, and you will be enjoying their seedlings for years to come!
So there you go, a quick and simple - although not very pleasant - job to do in the garden this week: pull out all the dying Forget me not.
Oh, and don't put them on the compost heap, otherwise you will have thousands of seedlings popping up everywhere!