It doesn't require a lot of yarn, but I think these work better with a clear cut yarn rather then a fuzzy wooly one (sorry for the lack of technical terms there).
1, make a slip knot leaving about 8-10 cm of 'tail'
2, chain 5
3, attach the last stitch to the first one with a slip stitch (pull the yarn through both stitches in one go), so it forms a nice little circle (with 5 chains - one for each petal of the flower)
4, chain 3
5, make a double crochet (in the UK that would be a trebble I believe) into the circle
7, attach the chain with a slip stitch to the chain of the circle. You might need to wriggle the chain and the double crochet to the side a bit so the the chain stitch where the petal attached becomes visible - this is the afore mentioned fiddly bit. I found it helped if I used my left hand (thumb and pointer) to 'hold' the space whilst crochting the petal with my right hand. Sadly I couldn't photograph this bit, because I was out of hands :-)
8, this is one petal finished. You now repeat these steps another 4 times until you have 5 petals in total. Once you attached the last petal, you do another (one) chain stitch then cut the yarn leaving a tail of about 8-10 cm and pull it through the last chain. The first 'tail' should be right underneath the second tail so I usually double knotted them, because that tightened up the flower ring a little and made it prettier.
9, To attach a second flower:
you finish the first petal and start on the second one by chaining 3 and making one double crochet into the circle. Then you remove the needle and put it through the top of a double crochet of the flower you want to attach it to.
Next you simply pull the loop through.
Then you chain 3 and attach the chain to the circle. After that you continue with the rest of the petals. As my scarf had 2 rows I also attached a flower to the 3rd petal.
Here are the two flowers finished with the tails knotted
To finish off: usually I just weave the yarn in with my crochet hook, but I thought it would look prettier if I use a yarn needle (they are the big ones that don't have a sharp point) and thus reinforce the circle as well. So, with one end I went around clockwise and with the other end I went around anti-clockwise.
I think it tightened it up rather nicely in the end.
Happiness in Crochet :-)