This DIY uses up your old cut offs of decking and does not take too long providing you have access to a trusty 'chief holder' (my job) and somebody else (patient other half) to screw all the sides in whilst you're doing a grand job of holding it all together. Cut six bits of deck the same length (ours are 50cm) and four pieces for the sides (roughly 20cm depending on how deep you would like the boxes to be and to cover the depth of the base).
Assemble by screwing through the ends of the smaller pieces to the front and back and again with the two bits for the base tucked up inside. Complete by using two small pieces of deck (roughly 10x10cm) and place these underneath your planter. Screw down into these two pieces to stabilise the base and also to raise it off the ground for easy drainage.
To protect the wood from rotting, line with a length of plastic tarp and pierce the base with a knife to allow the water to drain. Fill with soil, pop your lavenders in (here we used three French lavender in each planter) and sprinkle a few stones or pebbles around the plants to keep in the moisture for the summer months (hugely optimistic I know). Finish up your hard work with a glass of wine in the sun. Job done.