Most of my art is painted from a live plant from a garden. This can present problems of course – when a flower is brought into the heat of the studio it can start to open further, and it can turn from the position you’ve set it in towards the light. So sometimes you end up trying to paint a flower that has arranged itself differently from the one you drew.
My tip is to try to stay with what you’ve drawn, and rearrange the flower to try to facilitate this. For example rotate the flower every few minutes to try to get the same pose as the one you drew.
Alternatively, bring the plant indoors a few hours before you are ready to draw and paint, in the hope that it will have settled by the time you are ready.
Another source of plants is the local supermarket. Look out for plants that are reduced, like this rose, to help keep costs down. Even the most battered looking plant will show some signs of life when looked after, and you can often plant it outside again afterwards for some colour next year.