take pieces of stalk that are firm but not woody, cut all the leaves off except the top two, I usually then cut the two remaining leaves in half. stick them in some potting soil and keep moist, and after about a month theyll usually have some roots on them, thats it, you then have new plants to put on your deck.

The advice above is good, and yes you are quite right to take the cutting just below where the leaf stalk joins the stem (it's technically called the "node" but it doesn't matter what its called. Taking the cutting just below the node is useful as the stem is firmest here and there are lots of plant hormones in these areas that will help rooting.

Don't forget to remove the bit of stem left on the parent plant , cut it off just bove the next node down, otherwsie the stem can rot back into the plant, and anyway it looks ugly if there are dead bits of stem sticking up.

They will root in water but personally I prefer to put them into a pot with 50/50 peat substitute (compost) and grit.

Good luck with your pelargoniums and geraniums, they are great plants.

Tony