Ask Mark Cullen

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Your spring gardening questions answered

Master gardener Mark Cullen answers reader questions about veggie gardens, pest control, composting and more. Mark appears on Canada AM and 680 News radio, and is the gardening spokesperson for Home Hardware. Sign up for Mark’s monthly newsletter at

Mandy asks: We're excited to start a corporate vegetable garden this spring for employees and local charities - what veggies are best?

Mark answers: The choice of veggies depends on space and soil quality.  Many vegetables are great in small spaces and others are space hogs, relative to productivity.  Beans, staked tomatoes, peppers, staked peas, radishes and carrots are relatively productive in small space while all squash/pumpkins, corn and brassicas are poor choices for productivity.

Robert asks: Is there a way to get rid of tomato hornworms on plants that doesn't harm the environment?

Mark answers: Hand picking is the best alternative.  If this ‘grosses you out’ wear a pair of gloves and drop the horn worms into a container of water with veggie oil floating on top.

Beverly asks: We have a small backyard, mostly lawn. We want to convert most of the lawn to vegetable and flower beds. What's the best way to deal with the grass that won't break my back?

Mark answers: Don’t try to remove the grass, leave it there and cover it with 20 to 30 pages of newspaper and let it rot underneath; cover the newspaper with 30 cm of quality triple mix and plant in that.  A raised bed or ‘wooden box’ helps to hold the soil where you need it.    Be sure to buy good quality soil – this is not a good place to ‘save money’ on poor quality.  This method will not work well with root crops like carrots and potatoes unless you increase the depth of the new soil dramatically.

Wendy asks: We live on a heavily treed lot where the only sunny spot is our septic bed area. Can we build a raised vegetable garden on top of or near the septic bed? Is it safe to use pressure treated lumber to build the vegetable bed?

Mark answers: You can build up the soil on the septic bed with quality triple mix.  Pressure treated wood is much safer now that they have taken the toxins out of the treatment.  Still, I would not grow root crops up against the treated wood, just to be safe.  

Rachelle asks: Where is the best place in a yard to put a compost bin? Can you compost things like newspaper and sawdust?

Mark answers: Locate a compost bin in a sunny position for fastest results.  Be sure to water it in dry weather and turn it every 4 to 6 weeks for best results.  You can compost sawdust and shredded newspaper when they are mixed generously with ‘green’ yard waste like grass clippings and kitchen scraps.

Sandra asks: I live in a basement apartment in Toronto with almost no light. Are there any plants that will grow without using artificial light?

Mark answers: Not many.  Some will survive (vs. thrive).  My list includes Spathaphilum (White Flag), arboricola, wandering jew, ferns and dracaena marginata.