The stalls might be selling predominantly orchids. But I have only eyes for roses...
(1) Roses love to drink coffee. Just kidding. Feed them coffee grounds for these beautiful suckers love acidic soil. Dry the coffee grounds first before putting them on the soil. I'd cover with a layer of soil, then pour some water to release some needed nitrogen into the soil. Btw tomatoes love coffee too.
(2) Roses also like egg shells. The usual approach would be to bake the shells then grind them before feeding them to the plants. Baking is for preventing salmonella. But what I do so now is to boil the egg shells. Same function, and I feed the egg-shell-boiled water to the plants as well. I don't grind the egg shells though. I prefer to pound them with something hard to shatter them into little bits. Get a little workout!
(3) I drink pu-er tea nowadays. I don't throw away the leftover dregs. I feed them to my roses. Don't put them near the stem though.
(4) Cloching stem cuttings with plastic bottles do very well for roses. Much better than soaking them in water, which takes forever!!! I soaked one cutting for months, never getting anything. Instead, once I did the cloching method, I got roots like in 2 weeks!
(5) So about the cloching method. I had read that we should use stem cuttings that are about pencil thickness. But I have used thinner ones and succeeded. What you do is that if you have the thick stems, you cut a cross on the bottom of the stem. Then either dip that end in rooting hormone/honey/nothing (which is what I did), before planting it in moist soil. Put a plastic bottle (which you have cut the bottom off) over it, creating a little greenhouse, and let it grow roots. Only release the bottle once a week for oxygen, otherwise leave it alone. After a couple of weeks, tug at the stem gently. If there is resistance, then the rose has rooted.
(6) For stem cuttings that use soaking method, I think that cutting new shoots is the best way to go. You might have to sacrifice the potential of new blooms this way, but I have found that cutting new shoots and soaking them is pretty effective. Only about 2-3 weeks before roots will appear.