The Dahlias have been a hit this year! I have grown Dahlias since we bought our first house over 20 years ago. I have experimented every which way with how to grow them. I spent years digging them up and storing over winter until one year I simply couldn't find the time and left them in. They were all fine, and that was without a mulch through a mildish winter. From then I have always left them in with a good mulch and even after the 'beast from the east' they miraculously sprouted again the following spring.
You can of course pinch out the growing tips to bush them up but after trying this and not doing it, I find if you have a million other things to do in spring and you don't get around to it, the act of cutting for the vase and deadheading does the same thing as long as you have planted them early enough.
The foliage is susceptible to frost but if it is just a light frost, they will soon recover so don't panic. If a heavy, late frost is expected a layer of horticultural fleece can be really helpful.
Just like any young shoot, slugs and snails might like a munch so a protective ring of something can help. Mine are mulched with PlantGrow and as it dries out, I find they don't much like to crawl over it.
Watering is a surprise. When they are young they may well need regular watering but I have tested them to the absolute maximum and throughout dry, hot weather I have been able to leave them almost two weeks before giving them a big soaking. Water directly into the soil which should be mulched. A heavy mulch will help to retain that moisture for a longer period. Don't forget the key is with good soil.
Planting lots together (yes the more the merrier) will help to not only shade the soil and keep it cool in hot weather but also help to support each other. So I have never supported my Dahlias!
Basically many plants are way more resilient that you think, just experiment and find your way. I often find we complicate things and rather than observing and learning along the way we hurry and want instant results. Plants want to grow - we just have to help them along.
You can see more photos HERE.