S@H: What are the biggest mistakes beginner gardeners tend to make?
Mark: That's easy. They don't prepare soil properly or thoroughly enough. First determine what kind of soil you have. It's going to be between two extremes: solid clay and pure sand. In Ontario, the majority of people have clay-based soil. You don't want to plant your whole garden in that. Before planting a whole bed, dig out 16 inches (40 cm) deep and fill it in with “triple mix.”
Triple mix is a combination of top soil, compost and peet moss and it's the universally accepted soil mixture. Use it for ornamental gardens, fruit trees, roses, evergreens - anything. You can buy it at any garden centre. If you're just putting in one plant, remove the clay-based soil from the hole and fill that in with triple mix.
Once you have a good quality soil, 90 percent of your gardening success in ensured right there.
Now put the plant in the hole. The crown of plant (where stems meet the top of the pot) should stand 5 to 8 cm above the grade of the soil. Then mound soil up to the crown. You don't want water flowing down into the crown because then the water doesn't drain away and the plant will rot.
S@H: How often do I need to water my garden?
Mark: Most new gardeners, if they get this far and fail, it's because they over water.
I've seen more plants killed by an excess of TLC than anything else. New gardeners don't know that plants need to dry out -- the roots need to breathe.
If all you did was keep the roots sopping wet, oxygen would never get down to them. It's really important to let plants get somewhat dry between waterings. Notice I didn't say bone dry. Here's how to check: just stick your finger into the soil. It should feel dry for a couple of centimeters and moist further down. In time, you'll be able to look at your plants and know if they need water.
S@H : How do I choose the right plant for the location?
Mark: The primary consideration is light. Remember this rule of thumb: “Partial shade” is no more than 6 hours of sun a day; “full sun” is at least 6 hours of sun a day.
If you want perennials, you can't go wrong with low-maintenance, shade-loving hostas. You can grow them anywhere in Canada, up to north of Edmonton.
Coral bells or heuchera are my favs for partial shade. There are so many varieties with beautiful flowers (and slugs have no interest in them). They have a furry leaf and flowers from 12 to 24 inches (30 cm 60 cm) high. They make a beautiful show -- you could do a whole garden in heuchera.