Dear Anne,

Since I'm in Vancouver, some of the annuals in my containers sprout again the following year. I also have perennial plants and bulbs in some of the containers.

How do I deal with putting fresh soil in the pots? Is it necessary? Or can I simply continue to give them liquid fertilizer?

Michelle, Vancouver

Shrubs, trees, perennials, and anything that stays in a container for long periods need top-dressing in spring. That is, you remove the top inch or two of soil and replace it with something quite rich, like compost or potting soil mixed with a little fertilizer.

With your annual and perennial containers, you would then go on to feed liquid fertilizer through the summer, in the usual way.

But container trees and shrubs usually outgrow their pots after a few years and need a fresh change of soil and a bigger pot.

That can sometimes be postponed for a few extra years, by doing extensive pruning of the top growth.

But eventually, a soil change is necessary.

If no bigger pot is available, root-and top-pruning are needed, so the trees and shrubs can fit in the old pot along with the fresh soil.

With annual and perennial containers it's also best to repot in all-fresh soil every few years, because perennials - and even returning annuals - ultimately fill all the available soil with roots. At that point, they'll need extra space or division.

Dear Anne,

Some of the leaves on my Monarda didyma were darkening and curling inward, with a white frothy substance on the underside. Someone at a garden shop suggested a mixture of soap, baking powder, and water to be sprayed on the undersides of the leaves.

Now the leaves are spotting and curling, and I had to remove some that practically fell off. The plant looks quite unhealthy - it used to be the most robust in my container garden.

The Ray Kennedy, email white frothy substance is a foam which protects a little larvae called a spitbug. Though unsightly, spitbugs don't hurt plants. But if they bother you, just remove them from the leaves. Or pick off the leaves.

I think the garden centre person misunderstood your problem and gave you an organic recipe for powdery mildew. Monarda is very prone to it, but powdery mildew is definitely not frothy. It's powdery.

The curling and drying is most likely caused by lack of moisture.

Monarda is a mint family member and does best in moist soil.

Containers are notorious for drying out when temperatures rise into the early 20s, and in those temperatures, it's best to water containers twice a day, especially if they contain moisture-loving plants.

Sometimes people com-bine moisture-loving and drought-loving plants in the same container. It makes watering very challenging.

If your monarda is dry at the roots for several weeks, it could trigger a real attack of powdery mildew.

Dear Anne,

I want to direct-seed beets and chard. Can I get going on that now? Is it warm enough? Or should I wait longer?

Colleen, email

Any time from the second week in May onward should be quite safe for planting seed of beets and chard.

Anne Marrison is happy to answer garden questions. Send them to amarrison@shaw.ca