How to revive False Sunflower?

Hi, I am a novice gardner and beginning to garden with simple, easy to grow wildflowers and the likes. I planted a couple of young false sunflowers and a coneflower plant I bought from Home Depot. They are in direct sunlight in a well drained moist soil. The coneflower is blooming but looks weak and twiggy with a lot of yellow dry leaves at the base of the plant. Both the false sunflower plants lost all their foliage. I simply trimmed them down to a couple of inches above the ground level. It has been a week now and the bare stems still seem firmly rooted. Is there any way I can revive these false sunflower plants? Please help. I love plants, but I am so bad at gardening. I spent about $300 on yard services and new plants from an "arborist" and I cannot afford any more this season. Please help.
Cheers, Sapn
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