Certified GKH Gardening Expert
It may be lacking phosphorus. I would give the plants some phosphorus, like bone meal. If the foliage looks healthy but there are no blooms, phosphorus is normally the problem. This article should also help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/phosphorus-plant-growth.htm
They may also be overcrowded. If this is the case, simply dig them up and divide the plants, transplanting elsewhere.