Delphinium enjoy a rich organic soil

I was wondering if you happen to know what might be causing my delphinium to not come back or to be very small and not bloom when it does return? It seemed to do fine when we were in our town home a few years back — the soil was rather sandy there.

My husband and I are now in a new development that has clay under black dirt. I have (or had) my delphinium planted in full sun and in areas that were both flat and sloped and they just don’t do well. I’ve about given up and plan to not replace them with the same plant next year.

I am thinking that since phlox and Russian sage do so nicely, they will take over where the delphinium has failed me, though I do adore vivid blue flowers.

An additional note: I also have a “butterfly blue” delphinium that is more “branchey,” shorter, and loose in structure than the closely clustered single-stalks of the standard delphinium. I’ve had great success with those. Maybe that’s the variety I should stay with, but if you have any insight, please share with me.

— Chris

I’m not exactly sure what’s going on with your delphinium. They are a short-lived perennial, only persisting for three to six years on average (about three or four in my garden).

They should come back well through the first winter or two at least. If they’re not doing that, I would look into the situation they’re in.

Delphinium like a rich organic, well-drained soil with a regular moisture supply. If they dry out too much (even over the winter), they come back weakly, if at all. However, if they’re in a low spot that stays wet a lot, they will rot and fade away.

Actually, you sound like me and my gardening philosophy: When a plant fails, I don’t spend a lot of time agonizing over what went wrong. I switch over to something else that’s doing well.

The Chinese delphiniums (D. grandiflorum) are wonderful plants. You might look for a variety called “blue mirror” that has clear, azure blue flowers, a little lighter than “butterfly blue.”

These are great in the garden, providing clear blues and violets in the garden and are more “usable” in the bed with their bushy growth habit.

Another perennial that gives that color is balloon flower (Platycodon grandiflorus). There are different varieties in different colors, but the standard is a cool violet blue. Others you might look into include “Johnson’s blue” geranium (Geranium x Johnson’s Blue), “butterfly blue” pincushion flower (Scabiosa caucasica), speedwell (Veronica spicata) and blue flax (Linum perenne).

What’s the difference in what time of the year you cut back Russian sage: spring vs. fall? We usually cut ours back in the fall and have never had any problems, but I think I heard you mention once that it is better to do that in the spring.

— Keith

Actually, the difference is pretty minor. Cutting the plant back in the fall leaves open wounds that can desiccate over the winter causing some minor dieback.

As I said, this is a small point and probably doesn’t affect the plant very much in the long run. If it works better for you to do the job in the fall, go ahead and do it.

Just be sure to not cut them back too early in the fall as that can stimulate new growth late in the season, delaying dormancy in the plant and risking more substantial damage from early frosts.

Dennis Hill is the nursery manager at Bookcliff Gardens, Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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