• Start seeds indoors in the spring. (Photo: Mark Cullen/MarkCullen.com)

Mark Cullen is well-regarded as one of Canada's experts on gardening. He is the founding chair of the Highway of Heroes Living Tribute, writes a regular gardening feature column for the Toronto Star and acts as spokesperson for a number of organizations including SHARE Agricultural Foundation and the Canada Blooms Flower and Garden Festival. 

In 2016, Cullen was inducted as a member of the Order of Canada for his contributions to promoting and developing horticulture education in Canada and for his ability to explain how Canadians can protect the environment. 

On May 15, Canadian Geographic and Cullen teamed up for a Q&A on Twitter, answering gardening questions from our audience. You can find the full thread using the #CanGeoGardens hashtag, but here are his top tips.

Plant vegetables before mid-June

Cullen says mid-June is actually getting late for vegetables, but if you're itching to get your hands dirty you can plant perennials or container flowers any time all summer. 

“Each day you wait is one day you don't get to enjoy their beauty,” he says.

Plant native seeds or plants whenever possible

According to Cullen, native plants are more disease- and insect-resistant than non-native or hybrid plants. Native plants are also often more drought-resistant, contribute to local biodiversity, and can be more effective at attracting pollinators.

Think small, work with what you have for apartments and condos

Growing vegetables on your balcony might seem like a daunting task, but Cullen says simply avoiding space hogs like squash or corn is key. If your balcony is in the sun, plant tomatoes, peppers or lettuce. In the shade, plant leafy vegetables that don't fruit. 

Zone up for growing in pots

When growing in pots, especially trees, Cullen says to consider the growing zone you're in. Since pot-grown plants are exposed to much colder temperatures than when they're in the ground, go up two zones for growing in pots. 

Learn more about zones here.

Aphids and insects aren't causing as much damage as you think

If you're really worrid, spray in April or early spring, but for the most part Cullen advises that these little critters can be left alone — they tend to eat each other in their own circle of life.

Cullen and his son Ben have more tips, tricks and advice for all seasons on their website at markcullen.com.