One of the pluses of a perennial garden is that the flowers come back year after year. You don’t have to plant new ones each spring.

A downside, though, is that perennial weeds have a better chance at gaining a foothold in a perennial garden.

As in any garden, the best strategy is to keep weeds from spiraling out of control in the first place by prevention and regular weed patrols.

In vegetable gardens and annual-flower beds, gardeners can fall back on an annual weed cleanup once the garden is cleared.

That opportunity doesn’t come in a perennial garden. Not only can annual weeds pop up each year between the perennial plants, but perennial weeds can quickly entrench themselves among the perennial flowers.

When that happens, weeds are difficult to remove, and these aggressive growers can quickly overtake the planting.

Dealing with annual weeds in a perennial garden

Annual weeds that pop up from seed each year, such as groundsel, lambsquarters, pigweed, and purslane, are fairly easy to control.

A layer of mulch over the ground discourages them, plus weed preventers can be applied around most perennial plants to keep annual weeds from germinating without harming the plants.

Preen Extended Control Weed Preventer, for example, prevents the growth of more than 100 common weeds and gives season-long control with two applications per year (once in spring and once six months later in fall).

The product can be applied around hundreds of existing landscape plants. (See the label for plant-by-plant specifics.)

Preen Mulch with Extended Control Weed Preventer is a double-protection bagged product that combines wood mulch with a weed preventer.

Even when annual weeds sprout, they’re easy to pull because of their young, limited root systems. Most also give up easily when they’re sliced off at ground level with a long-handled weeding tool.

Dealing with perennial weeds in a perennial garden

Perennial weeds are much more “challenging” than annual weeds in a perennial garden.

Many of these spread by runners or underground stolons, entangling themselves with the desirable perennials.

Some of the worst offenders are bindweed, oxalis, wild strawberry, creeping charlie, quackgrass, and prickly Canada thistle. All of these weeds can regenerate when even a piece of root is left behind.

Mulch and weed preventers are ineffective against perennial weeds once they’re up and growing.

Trying to spot-spray herbicides is risky because of the possibility that spray drift will harm the perennials along with the intertwined weeds.

That leaves mechanical removal as the most viable option. Hand-pulling is a possible solution if you get to the perennial weeds when they’re young, and if you’re persistent enough.

Another option is digging up weed-entangled perennials, removing the weeds and their roots, then replanting the perennial.

When things really get out of control

When the whole perennial garden is overrun with weeds, the best solution may be a complete revamp. This involves digging the whole garden, separating the perennials from the weeds, then replanting the garden.

Early spring and early fall are the two best times of year for a total re-do.

First, dig your “keeper” plants and sink them in a temporary holding bed. You can pack them close together. Just label them, and give them a good soaking for their short-term stay.

If you don’t have a temporary planting space, group the dug-up perennials in a shady spot and cover their roots with damp mulch, leaves, or straw (to keep the roots from drying out).

Then tackle the weeds by either digging and removing them or spraying them with a kill-everything herbicide. Be sure to remove weed roots from the perennial rootballs.

If you’re digging the weeds, you can immediately replant the cleared-out bed. This is also a good time to work an inch or two of compost into the soil and to divide any big clumps of perennials.

Apply two inches of organic mulch and a weed preventer to discourage new weeds from immediately sprouting in the disturbed soil, then give the bed a good soaking. Keep the soil consistently damp for the first full season since this is essentially a new garden again.

If you’re using an herbicide to kill the weeds, you’ll have to wait a week or more to replant. Check the label of the product you’re using for details on the interval between application and safe replanting.