I did two naughty things with my Euphorbia Cushion Spurge this year. I planted it under a Honey Locust through which there is a dappled shade (I have since discovered it should be in a more sunny locale) and I did not cut it back after flowering in the spring. It is now sprawling all over the bed, limply. Would it be a disaster if I were to cut it back now, or should I wait until after flowering next spring?
Your kind advice is appreciated.
Euphorbia polychroma, commonly called cushion spurge, is a very attractive spring blooming perennial that does best when planted in full sun to partial shade. It is tolerant of most soil types but prefers a fairly dry, well drained location. Propagation is done by seed, cuttings or division. If not deadheaded after flowering, it will more than likely, seed itself in your garden beds. Divisions can be made in the early spring or fall. Once this plant really gets established in one location though, it doesn’t like to be disturbed and may be setback.
In your case, I think the best option is to dig up and move your spurge now and plant it in a sunnier location in your garden. Take as much of the root ball as you can get, move it to a pre-dug hole and plant it at the same depth. Water the plant in well after re-planting and continue to water until freeze up. A 3 inch layer of mulch around the base of the plant will help retain moisture in the soil and will also provide some insulating protection. If you do this, the plant will have time for its roots to get established before the ground freezes for the winter.
As far as cutting back the plant, you could now cut a maximum of one third of the stems back to 4 inches, leaving two thirds available for spring blooming – I would remove the longest straggliest stems and any that are damaged, mostly to tidy it up and make it easier to move.
Once the soil is workable in the spring, you could take back the mulch, top-dress with some well rotted manure or compost and then re-mulch. In early summer, after flowering, you can cut the whole plant back to 4-6 inches which will keep it bushy and compact.
Please remember that all parts of the Euphorbia plant are toxic so do not eat, and always wear gloves when making any root or stem cuts. The milky sap can be very irritating on the skin and painful if rubbed in the eyes.
Hope this helps.