This older petunia cultivar is down to its last blooms, but you can stimulate a full recovery and renewed bloom by cutting it back harshly! Source: www.plantwisdomgardencenter.com
Gardeners usually expect annuals to bloom all summer … and that wish generally does come true. However, some species, such as sweet alyssum (Lobularia maritima), edging lobelia (Lobelia erinus) and petunias (Petunia x atkinsiana), especially older varieties, begin to falter in August, becoming leggy, only blooming weakly or even completely stopping blooming entirely. This situation is exacerbated when the summer is especially hot.
The usual trick for stimulating new bloom on any plant—pinching out faded flowers—becomes almost impossible: there are so many faded blooms that individual deadheading is nigh to impossible. So, what can you do … other than just watching the plant go downhill?
Well, if you catch them on time, as soon as they start to bloom less (this won’t work if they’re reached the point where they’re nearly dead!), simply cut the whole plant back by half. Then after that, keep up regular summer care.
Such a radical pruning stimulates the plant to completely regenerate and it will soon be in full bloom and as attractive as ever!