This week I answer readers' questions:
Q: 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 these containers. How do I deal with these in regards to putting fresh soil in the pots? Is it necessary? Or can I simply continue to give them liquid fertilizer?
A: With shrubs, trees, perennials and anything that stays in a container for long periods, top-dressing in spring is the best practice.
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/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 pot after a few years and need a totally fresh change of soil and a bigger pot. This 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-pruning, and toppruning are needed so the trees and shrubs can fit into the old pot along with the fresh soil.
With annual/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.
Q: 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 underside of the leaves.
Now the leaves are spotting, curling and I had to remove some that practically fell off. The plant looks quite unhealthy now although it used to be the most robust in my container garden.
A: The white frothy substance is a foam that protects a little larvae inside 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 this, 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 low 20s and in those temperatures, it's best to water containers twice a day especially if they contain moisture-loving plants.
Sometimes people combine moisture-loving and drought-loving plants in the same container.
This makes watering very challenging.
I should add that if your Monarda is dry at the roots for several weeks, this could trigger a real attack of powdery mildew.
Q: I want to direct-seed beets and chard. Can I get going on that now? Is it warm enough?
Or should I wait longer? A: 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 her via [email protected].
