when to plant out multi headed sunflowers

Wilderbeast

i have 25 Ruby sunset multi head sunflowers. They are currently about 18 inch tall in 2 lt pots and should get up to 1.5mt tall. they were potted on only a week ago and the compost is already white over with roots. So FIL who grows of sunflowers says i should pot on again but its loads of compost and hassle to keep them watered and thought i could plant them out. Thoughts please 

CharlotteF

I'd get them in. 18 inches ought to be big enough to be safe from slugs and snails and that's the only reason I'd not transplant small plants at this time of year. Certainly warm enough for them, finally.