They like a lime rich, well drained soil in full sun. Possibly the yellowing ones have been over-watered? They definitely do not like that.
I am just about to plant out the ones I have grown from seed so putting your out should be possible now as long as they have been hardened off.

Also very important to keep the area well weeded. They are easily overwhelmed by noxious weeds, couch grass, etc. Don't crowd them in with other plants. They like rich fluffy moist soil with good drainage, full sun & good air circulation.

I wonder if she put them out when they hadnt been hardened off. Many GC dont harden them off and although outside the main building they are under shelter.

Do heathers and rhododendrons do well in your garden? If so the soil may be too acid for pinks. Try treating the ground with lime before planting.

Many moons ago, I asked for advice on growing pinks in a pot. I'd been feeding and watering regularly and was advised that they "thrive on neglect". I watered more sparingly and stopped feeding and have remembered that advice ever since. Since then, I still grow them in pots and take cuttings every year and I'm pleased to say that they take very easily.

What a very helpful set of replies! Thank you all so much. I think my friend might well have over watered and maybe put them out too soon. Mine have been outside in their little pots but sheltered among bigger pots. On the strength of all this advice I think I'll put half in bigger pots and half in the border. My soil is fairly neutral but certainly azaleas and rhododendrons don't like it much. I will add some lime to the pinks as suggested anyway. Thanks again.

Probably don't need lime if the rhodies don't like it though.

These are what I refer to as Prima-Donnas in the garden: everything must be just so. But I love the sweet/spicy fragrance they give and they make nifty cut flowers too - the popular carnation (D. caryophyllus). You can earn big $$ growing these for the florist trade. They are always in demand.