"I don't fertilize much"

A good place to start. Top dress with some good compost.. save yourself the work of digging it all up.

Root pruning.. cant hurt to remove some of the larger ones.

Spruce trees have notoriously shallow and thirsty roots. If you're going to keep gardening in the vicinity of one you need to fertilize and water like a maniac. Or cut down the Spruce like I finally did!! Made all the diference in the world.

Steve

I have a similar problem because I planted a perennial garden under an Aspen tree. I added soil to raise the grade thinking that would help the new plants, but the Aspen roots just grew up into the new soil. The flowers planted in this area are somewhat stunted but a few varieties seem to do alright. My advice would be to simplify the bed and stick with a few plants that can tolerate the competition from your spruce. I don't have the option to cut down my Aspen as it's the only mature tree in the yard, so I just try to adapt my plantings to the difficult location. Joe pye weed and black eyed susans do well in this spot.

Thanks all. I am relieved to know that digging it all up won't help. I will fertilize more and try root pruning. I thought I might kill the tree by doing that.

Exactly how does one go about root pruning? Just cut the roots I find out?

I tried root pruning with a Silver maple, a lot of work & didn't help much. As a matter of fact, I think root pruning actually stimulated new root growth & made the problem worse. Finally got smart & cut the tree down.

I too, learned the hard way, that perennials can't compete with trees, especially as they grow up. Any methods you employ are only a stopgap. Make a choice. Flowers or trees. Any trees should be alone in their beds, and away from flower beds. Even Hosta and bishop weed eventually die out. Pondy

I have planted under trees with great success. I love to plant "tree rings" of hosta, daylilies or bishops weed. My favorite arrangement was under a black walnut tree and consisted mostly of bleeding heart, hostas, vinca, columbines, asiatic lilies & lilies of the valley. Obviously, some of these bloomed at different times. However, with generous compost and some mulching, all were quite healthy. The bleeding heart got about 6 feet across, so I don't think it suffered. I never bothered to try to prune any tree roots. Trunk diameter at eye level on the walnut was at least 2-1/2 feet - yes, diameter; and the garden itself had a diameter of about 10 ft. Best of luck.

I second what skeip said:
Spruce trees have notoriously shallow and thirsty roots

I planted Hostas under a spruce tree, only to watch them grow smaller and smaller every year. Transplanted the Hostas to a place where there were no tree roots in competition for water & nutrients, and they thrived:)

Planting around and under Black Walnut trees will give more successful results, as botanierra mentioned, because the roots of the Black Walnut reach deeper into the soil. Some plants do not tolerate the juglone in the soil around BW trees, but a person can experiment.

Planting around Oak and Honey Locust trees also works well.
But I digress...back to planting under the Spruce tree...You might consider planting in containers above the ground. Shade loving annuals would look great. I don't know if perennials planted in containers above ground would survive zone 5 though, unless you mulch and cover them somehow for the winter. Has anyone done that in zone 5?

Julie