April is the month to tend to flowering plants

Fertilizing flowering plants — perennials, annuals and roses — always makes the list of April tasks. But with a summer drought anticipated in the region, water conservation is a first priority, so I recommend fertilizing less than in a year with more normal weather. More fertilizer means more growth, which requires more water to maintain.
Perennial plants such as peonies, summer-blooming lilies and daylilies, Shasta daisies, and columbine — all the flowers you'd like for a bouquet in the house — will thrive nicely on one moderate fertilizing during April. If you did it in March, the flowers will not need it again. I use a kelp-based fertilizer with a 6-8-8- ratio and apply it only once a year. If the soil has been well-amended with compost and a fertile mulch — one derived from animal manure — you could skip the spring perennial fertilization altogether this year.
Rose care
For roses, fertilize after pruning, as many of you have already done in March, and then in June after the first set of blooms, instead of the monthly dose that is often recommended.
Fertilizers with organic sources of ingredients — those derived from living materials like cottonseed and kelp — supply nutrients slowly and help with steady rather than too-fast growth.
Chemical fertilizers with lots of nitrogen shove the plant into hasty leaf production, which is just the opposite of what's desirable in dry seasons. Use soaker hoses or other efficient methods to water roses.
What to trim, deadhead
Shearing plants fits into the April schedule as well. Hedge-trimmers, hand-powered or electric, work well on bloomed-out spring ground covers such as white candytuft (Iberis sempervirens) or ground-cover phlox (Phlox subulata).
Removing the flowers, but allowing the foliage beneath to stay intact, will help the plant produce fresh foliage that looks attractive all summer. Shearing also works on herbs that went through winter with ragged flowers or foliage.
Trim sage, rosemary, lavender and artemisia to shape. For years I've used a pair of sheep shears that wandered into the garden tools somehow, giving me the spring impression of shearing woollies as well as bloomers.
Caring for rhodies
Rhododendrons and azaleas will roar into bloom this month, and their faded flowers bring up the question: Do I deadhead these things, or not?
Gardeners at the Washington Park Arboretum grow thousands of rhododendrons, many of them far too large for removing the spent flowers. They bloom on without flower deadheading. If the rhododendron is very small, such as the 1-foot 'Blue Diamond', it will generally drop flowers just the way all azaleas do. So if it's too tall to reach or covered in tiny self-cleaning flowers, no action is needed.
But when the plant shines prominently in the landscape, most gardeners take the old flowers off to improve the beauty of the plant. Some research indicates that the shrubs flower better in the following year if they aren't throwing energy into making seeds. The choice is yours.
Rhododendrons certainly look sleeker in the landscape when they aren't daubed with brown seed heads. Deadheading is difficult to do with gloves on, so expect sticky hands from the sap.
Round up thirsty plants
Flowers requiring ample summer moisture — calla lilies, primroses, filipendulas, astilbes and Japanese iris — should be grouped and given their own soaker hose or other irrigation.
What to plant
Besides being a good time to tidy up the yard, April is also the time to start work on a vegetable garden. "The Maritime Northwest Garden Guide: Planning Calendar for Year-Round Organic Gardening," (Seattle Tilth, 2000), suggests the following vegetables for planting this month: radishes, carrots, beets, broccoli, onion sets (for small salad onions), spinach, bok choi, snow peas, sugar peas and potatoes (from seed potatoes).
Vegetables to start indoors for late May transplant when the soil warms include these heat seekers: tomatoes, squash and basil.