This is quite a big exercise to complete. I mentioned today that you paint the sky first and you can paint distant trees. This gives you the shape of the upper flowers (negative space). You can go back as I did when the painting is three quarters finished and increase the palette on both the sky and trees. This all depends on your perception of tone: if you paint in light tones do not follow that procedure.

Remember to use a range of reds of the flowers from cadmiums to purples. If you only use one red it looks flat. A Good Palette: Cadmium Red, Brilliant Red, Spectrum Red. Add a small proportion of blue to the darkest red to make
a purple and use this at the base of the flowers where they meet the stem.
Trichomes a plant hair or outgrowth from the epidermis, these are fun to complete! Take a fan brush (appropriate size) wet edge and apply to white gouache. These trichomes are all over the plant stem and buds to protect them from getting eaten by insects. Apply the white (last thing you do in this painting) over the stems and buds, use a short brush stroke.

The foreground background, use wet on wet and apply all the colours in your palette that you have used. This is the practical way that any artist works to use up the remainder of a palette.
You will need to increase the tone of the stems in the foreground.
I worked on this painting all afternoon in the garden. Get way to spend a sunny afternoon!