As cold winds and rains move in, we need to consider how to protect heat-loving plants like calla, canna and dahlias. Here are some tips...

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As cold winds and rains move in, we need to consider how to protect heat-loving plants like calla, canna and dahlias.

Here are some tips on caring for these tender plants so they can flourish again next year.

Dig and store

Twenty years ago, the method for protecting dahlias, cannas and callas from freezes was to dig them up.

There’s nothing wrong with digging — especially if you’re planning to redo the garden in the spring. (Local dahlia growers dig up their crops in mid-November in order to divide plants and prepare for spring shipments.) However, the digging method can be time-consuming.

You’ll need to unearth the plants after leaves die back, shake off soil, tie on an identifying label, expose bulbs to air for two or three days and store in slightly dampened vermiculite or peat moss.

The bulbs need to be in a cool but not freezing cold shelter. An unheated garage or a dark basement corner would work.

If your garden is in the foothills of the Cascades or east of the mountains, digging and storing is the best way to go.

Leave ’em be

Milder winter temperatures over the past 15 years have given many of us the courage to leave summer bulbs in the ground through winter.

The main requirement for leaving bulbs in ground is well-drained soil. These heat-lovers rot easily and won’t survive if they’re waterlogged.

When frost arrives, the plants will stop growing. Trim off the dead leaves in mid-November. Pile about 4 inches of mulch over the plantings. It’s helpful to place a small marker to remind you where the summer bloomers are planted.

The plants will begin to grow again as the soil warms in the spring.

Special cases

If you’ve enjoyed summer bloomers in containers, the question of how to protect them through the winter gets a little more complex.

Success depends on the size of the pot and the amount of soil around the root.

The bigger the pot — such as anything from 18 inches in diameter and up — the better the chance of survival.

Containers less than 12 inches in diameter can freeze solid. Take summer-blooming bulbs out and store as suggested, or discard them and start over again in the late spring.

Some calla lilies (Zantedeschia aethiopica) may need special consideration.

The small, colorful sunset-colored calla lilies succumb to cold more easily than others and should be dug up and stored.

The classic big white ones are hardy in the ground and can be left once established. Leaves will be killed back, but the rhizomes will persist even if temperatures drop to 15 degrees.

Garden expert Mary Robson, retired area horticulture agent for Washington State University/King County Cooperative Extension, appears regularly in digs and in Practical Gardener in Northwest Life on Wednesdays. Her e-mail is