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Begonias and Dahlias

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Begonias and Dahlias

Start planting these bulbs indoors now for a summer spectacle in your garden

At this time of year, gardeners are anxious to start their spring planting. We encourage you to pot up some summer flowering bulbs, indoors. Not to be confused with ‘spring’ flowering bulbs, like tulips and daffodils, which you plant in the fall. Summer flowering bulbs are planted now through spring, for the most part. Two of our favourites for early spring ‘potting up’ are tuberous begonias and dahlias.

Tuberous Begonias

We absolutely love tuberous begonias. If you have partly shaded areas in your garden (they prefer eastern exposure), give them a try. They perform best in ‘dappled’ shade. Avoid total or dense shade. We guarantee they’ll impress you with their blooms.

Tuberous begonias provide a wide range of flower and leaf colour in low-light areas of your garden ALL summer long. They aren’t difficult to care for, and if you pay a little attention to them, you’ll be rewarded with luxuriant plant growth. With large double blossoms, we consider them the ‘roses’ of the shade garden.


The time to start tuberous begonias indoors is in the month of March. They should have two to three months head start before setting them outside at the end of May.

Make sure the tubers are in good shape when you purchase them. Pick up some peat moss and a shallow growing tray if you don’t have them at home. You’ll also need clay pots that are four inches in diameter (one for each tuber), some quality potting soil and a good water-soluble fertilizer for flowering plants.

How to start

Spread a layer of peat moss in the bottom of your shallow growing tray, then place the begonia tubers hollow (concave) side up in the peat moss. Sprinkle enough peat moss in another layer to just cover the bulbs. Keep the peat moss lightly moist until the tubers (or bulbs) have developed substantial roots (about an inch long). Place the tray in a warm spot while the roots are forming. The top of the refrigerator works well. Once white roots have reached two or three centimetres long, pot each tuber up in a four-inch clay pot with good drainage and sterilized potting soil. Place the pots in a sunny window until top growth starts and then pull them back from the light if it’s too bright.

Fertilize your new begonia plants every three weeks with Pro-Mix Multi-Purpose 20-8-8 and keep them well watered but not soggy.

At the end of May, plant the begonias in shaded, protected areas of your garden or in pots and keep them reasonably watered all summer long.

Tuberous begonias are wonderful in hanging baskets. Pot some up now and we know you’ll be pleased.


Unlike shade-loving begonias, dahlias love the heat and sunshine. To get the best show out of dahlias, you should
really start them in March in large, gallon sized pots. Use quality potting soil, like Pro-Mix premium potting mix, and place them in a sunny window to put down roots and begin to sprout.


If you have dahlia tubers stored in the basement from last year’s crop, it’s time to bring them upstairs. Separate the viable/healthy tubers and get potting. What you cannot accommodate in your house you can give to willing recipients in the family or neighbours on the street.

Not all summer flowering bulbs require an early start. Gladiolas will perform much better planted directly in the ground come late April. Space the plantings apart by about two weeks over a couple of months to create a succession of bloom.


Give summer flowering bulbs a try this spring for a great show all summer.

Mark Cullen is a Member of the Order of Canada. He reaches over 2 million Canadians with his gardening/environment messages every week. Receive his free monthly newsletter at www.markcullen.com Ben Cullen is a professional gardener with a keen interest in food gardening and the environment. You can follow both Mark and Ben on Twitter (@MarkCullen4), Facebook (https://www.facebook.com/MarkCullenGardening/) and Instagram (https://www.instagram.com/markcullengardening/).


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