Answer: Based on my experience, the problem is mostly that PA summers are just too hot and humid for these plants. Some gardeners grow them as annuals for this reason, and just plan on replacing them with blooming size plants each spring. One way to enjoy the delphinium blue in the garden is to grow larkspur; it is short lived also but will self seed where conditions are right.
Here are some tips on growing delphiniums if you want to keep trying. Keep in mind that full sun all morning will be cooler than full sun all day long; provide good air circulation to try to limit foliage diseases, and also provide evenly moist yet very well drained soil to avoid root rots.
Give lupines sun all morning and a well drained soil as well. Lupines will grow well in a slightly acid soil, but for delphiniums you may need to add lime to bring the soil pH up to about 6.0. I hope this helps!
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