Some of the plants you can use for natural dyeing.

Flower is yellow and has four tiny flower petals
3 mm across
grows to a height of 10 cm
flowers in July and August

Picture

Lady's Bedstraw
In addition to being a dye source for red and yellow colours, Lady's Bedstraw has been used for curdling milk and is used as a cheese rennet. It was also used for treating urinary diseases, and ointments.

How to Dye with Bedstraw
The Lady's Bedstraw is similar to the White Bedsraw. It's roots can be used to produce a red/pink dye, and is also part of the same family as madder. The leaves will produce yellow dyes.