Answer: If you're repeatedly having difficulty growing pansies, I suspect the soil isn't draining well, causing root rot and collapse of the stems. In my Seattle area garden, I also have a problem with slugs and they tend to feed on the stems and crowns of the plants. So, you may be dealing with both heavy, poorly draining soil, and slug attacks.
For optimal growth, amend your soil with some organic matter (compost, etc.) to help it drain quickly. Plant your pansies at the same soil level as they were growing in the nursery pots. Water deeply after planting, then water once or twice a week (depending upon rainfall). You can feed your pansies with a side-dressing of 10-10-10 fertilizer, or you can use a diluted liquid fertilizer (according to label directions) every 2-3 weeks during the growing season.
Pansies respond best if you deadhead them routinely. Simply pinch of the faded flowers along with several inches of stem. This will keep the plants from putting all their energy into seed production, redirecting it instead into flower production. Pinching out the faded flowers helps keep pansies compact, renews and invigorates them for a long season of bloom.
Best wishes with your pansies!
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