Binetti: This year, color your garden blue

On GardeningMay 28, 2014 

Georgia blue speedwell forms a carpet of blue flowers.

COURTESY OF LES PARKS/MCT

The fourth week of May is a time of exceptional color in Western Washington gardens but also a time when many local gardeners are singing the blues — and enjoying blue blossoms. Here are questions, with answers, about blue blooms.

Q. I want a garden with more blue flowers. Can you help me with some plants (other than delphiniums – they are hard for me to grow) that have true blue flowers? — P.L. Renton

A. The best blue blooms are on cool-season alpine plants, such as the rock garden gentians, and the best place to see those wonders of the plant world is at the Bellevue Botanical garden in their spectacular rockery. Not only is admission free, but the garden boasts one of the best perennial borders this side of the Atlantic Ocean.

If you don’t have a rock garden, then I’d suggest growing blue forget-me-nots and blooming sprays of blue brunnera in the spring, as well as true blue corydalis varieties such as “Blue Panda” and “China Blue.”

Summer blooms from lobelia, in either the trailing or more compact upright varieties, are easy to grow in an area shaded from the hot afternoon sun. Also consider the blue balls of blooms from agapanthus and the flowering onion and tall spires of purple blue Monkshood in late summer.

Blue iris, blue balloon flower, blue century plant, and blue lupine are easier-to-grow perennials — if planted in the right location. For more of a challenge, try growing the Himalayan blue poppy or Meconopsis.

Q. I know all the tips for growing delphiniums. I start my plants indoors from seed that I order from England. I coddle the seedlings in a greenhouse and don’t set them outdoors until May. I add plenty of compost and also Osmocote as a slow-release plant food.

I surround the plants with slug bait and support the weak stems with tall cages of twine and planting stakes. I do love my delphiniums, but here’s the problem. I can only get the plants to grow well for two or three years. Delphiniums are supposed be perennial. How do I keep mine producing well for decades without having to replant? My grandmother claims her old-fashioned delphiniums bloomed in the shade for 20 years without replanting — and my grandmother does not lie. — B.C., Auburn

A. I am sure Granny never told a fib – but she could be mistaking Monkshood or Aconite for the delphinium. Both have tall spires of blue and purple blooms but only Monkshood will flower well in a shaded spot and return year after year without replanting. Delphiniums come in more intense shades of purple, white and blue and are known as “short-lived” perennials.

This means they are like Rose mallow and many other tall perennial plants — happy to blossom for two or three summers and then these drama queens retire and fade quickly back into the soil. No worries, you can now buy gallon-size pots of delphiniums in bud or bloom and add them to your garden bed for instant impact — just remember all delphiniums need staking or their flower-filled stems will bend to the ground in the first rain or windstorm.

Q. I bought some blueberry plants because you wrote that they were easy to grow. I am writing to tell you my two plants only had a few berries last summer and they have not grown much. Please offer some advice. I am disappointed. — T., email

A. Blueberry shrubs are like rhododendrons and azaleas in that they love our naturally acid soil and plentiful rainfall. If you are trying to grow blueberries in a container, be sure to add two shovels of peat moss to the potting soil. Peat moss gives the soil more acid and also helps the potting soil hold more moisture.

Make sure the crown or base of the plant is not too deeply buried. It should be just half an inch under the soil. Top the roots with a mulch of compost or wood chips to keep them cool and moist. The mulch should be at least one inch deep, but two inches is better. Do not pile the mulch up around the neck of the shrubs.

Fertilize your blueberry plants in spring (or now if you forgot) using a rhododendron and azalea fertilizer. Prune out any dead brown wood and any tip growth that looks wayward and out of control but otherwise, blueberries do not require much pruning.

Do not disturb the fine surface roots of your blueberry plants by hoeing or raking and never let the soil dry out. Blueberries produce more in full sun but will also thrive and produce berries in part shade. Now if you will promise to do all of the above, I can promise you bountiful blueberries in a year or two.

Be sure to write back and let us know how many blueberry pies, muffins and pancakes you have been able to enjoy.

Marianne Binetti has a degree in horticulture from Washington State University and is the author of several books. Reach her at binettigarden.com.

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