Pruning Weigela is necessary if you want to keep the shrub in good condition with plenty of good sized flowers and healthy fresh foliage.
Weigela should be pruned immediately after flowering in early summer. As with many shrubs that flower at this time of year, they produce flowers on wood made in the previous season (year). If you prune your Weigela late in the year, then it will not have time in to grow mature wood for flowering next summer. If you prune your Weigela early in the year (before it flowers) then you will be cutting off the flower buds that developed last year, and there will be no flowers on it until the following year.
As soon as your Weigela has finished flowering, prune out all of the flowered stems by about one third of their length. This pruning will then prompt the Weigela to produce fine new shoots which will mature through the summer and produce plenty of flower buds for the next year.
At this time, it is also a good idea to carry out some regeneration pruning. This is done by pruning back hard, around one in every three main stems - right down to near ground level. New shoots will soon develop and grow to normal size - providing a good framework of healthy stems for future years. In subsequent years, again prune out around a third of all the older stems.
This pruning regime will apply to all of the popular varieties of Weigela including Weigela Abel Carriére. W. Bristol Ruby and Bristol Snowflake, Weigela Eva Rathke, W. florida types Foliis Purpureis (purpurea) W. florida Variegata, W. Looymansii Aurea, and all the other weigelas that flower early - Mid summer.