May Gardening Tips

May Gardening Tips
for the Willamette Valley

by Rod Smith

Former Iowa Certified Nurseryman and
Oregon Certified Nursery Professional

© 2002-2024 Rodney A. Smith
All rights reserved.


Annuals from seeds are best planted this month. Started plants can be planted outside. Fertilize regularly to keep them healthy and blooming.

Dahlias and Gladiolus can be planted outdoors. Use soil and bulb dust to protect them against insects and diseases.

Geraniums and Fuchsias, both upright and hanging, may be planted outside. If you have over wintered them indoors, set them outside during the daytime in a sheltered location, and bring them in at night,for a few days before leaving them outside so they don't suffer shock.

Planting a few perennials in bloom each month will insure continuous flowers in your yard.

Vegetables seeds and starts can be planted now. Plant bush beans every two weeks for a continuous harvest. Planting both early and late sweet corn will also extend the harvest season.

Spring Bulbs Care

Remove the spent flowers after they finish blooming so they won't use up energy producing seeds. Do not cut off the leaves because they are needed to store up food for next spring's flowers. Remove the leaves when they turn yellow and start to dry.


Prune spring flowering shrubs after they finish blooming. Remove spent flowers, also.

Broadleaf and needleleaf evergreens are best pruned or sheared just before or just after their spring growth. Pines can only be sheared at the soft candle stage, usually during May or June, when the needles are just emerging from the candles.


Continue to spray for leaf spot diseases as long as rainy weather continues.

Spray rhododendrons in late May for root weevils if the leaves have notches on the edges.

Check rhododendrons and azaleas for tiny, light brown spots on the underside of the leaves caused by lace bugs. Severely damaged leaves are almost white. Spray with a product containing Imidacloprid, such as, Bayer Advanced Garden Tree and Shrub Insect Control, or Spinosad, such as Captain Jack's Dead Bug Brew, to prevent lace bug damage. Both are toxic to bees, so do not use until flowers have dropped off.


Give a second feeding to bulbs, rhodies and azaleas when they have finished blooming.

Grapes should be fertilized with a high nitrogen fertilizer.
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