Alliums are a type of onion. The ones that you see most often are probably the big purple globes that bloom in the
spring. They smell unattractive to many pests, and can help deter aphids and such from eating your
roses. They also are deer resistant. If you decide to plant allium or other tall bulbs, I suggest planting them towards the back because they do get quite tall. Remember any perennial bulb that you want coming back year after year, you will have to let the leaves die off naturally. You shouldn't cut them down after the
flowers fade.
I suggest planting a variety of bulbs that bloom at different times to prolong the display. Usually, crocus blooms first, followed shortly by dutch iris (Iris reticulata). Muscari (grape hyacinth) follow behind them. Daffodils and tulips are divided into catagories (early season, may blooming, late blooming etc.)
Do note how deep the bulbs need to be planted. You want to be careful not to damage too many
rose roots (I did a lot of damage to an established butterfly bush when I dug too close to plant solomon's seal). In the
spring after the bulbs are past their prime, you might want to grow some low
growing annuals to complement the
roses. Alyssum works great with red/pink
roses.