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Monday, May. 12th 2014

May Gardening Calendar


  • Weeks 1-4: Apples, crabapples and hawthorns susceptible to rust disease should have protective fungicidal sprays applied beginning when these trees bloom.
  • Weeks 1-4: Pinch azaleas and rhododendron blossoms as they fade. Double flowered azaleas need no pinching.
  • Weeks 1-4: If spring rains have been sparse, begin irrigating, especially plants growing in full sun.
  • Weeks 1-4: Fertilize azaleas after bloom. Use a formulation which has an acid reaction.
  • Weeks 1-2: Canker worms (inch worms) rarely cause permanent damage to ornamentals. Use Bt if control is deemed necessary.
  • Weeks 1-2: Don’t remove spring bulb foliage prematurely or next year’s flower production will decline.
  • Week 1: Continue monitoring pines, especially Scotch and mugo, for sawfly activity on new shoots.
  • Week 1: Begin planting gladiolus bulbs as the ground warms. Continue at 2-week intervals.
  • Week 1: Plant hardy water lilies in tubs or garden pools.
  • Weeks 2-4: Scale crawlers are active now. Infested pines and euonymus should be treated at this time.
  • Weeks 2-3: Plant summer bulbs such as caladiums, dahlias, cannas and elephant ears.
  • Week 2: Begin planting warm-season annuals.
  • Weeks 3-4: Begin fertilizing annuals. Continue at regular intervals.
  • Weeks 3-4: Trees with a history of borer problems should receive their first spray now. Repeat twice at 3-week intervals.
  • Weeks 3-4: Bulbs can be moved or divided as the foliage dies.
  • Week 4: Pinch back mums to promote bushy growth.


  • Weeks 1-4: Keep bluegrass cut at 1.5 to 2.5 inch height. Mow tall fescue at 2 to 3.5 inch height.
  • Weeks 2-4: Mow zoysia lawns at 1.5 inch height. Remove no more than one-half inch at each mowing.
  • Weeks 2-4: Apply post-emergence broadleaf weed controls now if needed.
  • Weeks 3-4: Zoysia lawns may be fertilized now. Apply no more than 1 pound of actual nitrogen per 1000 square feet.
  • Week 4: Watch for sod webworms emerging now.


  • Weeks 1-4: Place cutworm collars around young transplants. Collars are easily made from cardboard strips.
  • Weeks 1-4: Growing lettuce under screening materials will slow bolting and extend harvests into hot weather.
  • Weeks 1-4: Slugs will hide during the daytime beneath a board placed over damp ground. Check each morning and destroy any slugs that have gathered on the underside of the board.
  • Weeks 1-2: Plant dill to use when making pickles.
  • Week 1: Keep asparagus harvested for continued spear production. Control asparagus beetles as needed.
  • Week 1: Begin planting sweet corn as soon as white oak leaves are as big as squirrel ears.
  • Week 1: Isolate sweet, super sweet and popcorn varieties of corn to prevent crossing.
  • Week 1: Thin plantings of carrots and beets to avoid overcrowding.
  • Week 1: Control caterpillars on broccoli and cabbage plants by handpicking or use biological sprays such as B.t.
  • Week 1: Set out tomato plants as soils warm. Place support stakes alongside at planting time.
  • Weeks 2-3: Place a stake by seeds of squash and cucumbers when planting in hills to locate the root zone watering site after the vines have run.
  • Weeks 2-3: Remove rhubarb seed stalks as they appear.
  • Week 2: Watch for striped and spotted cucumber beetles now. Both may spread wilt and mosaic diseases to squash and cucumber plants.
  • Weeks 3-4: Set out peppers and eggplants after soils have warmed. Plant sweet potatoes now.
  • Week 4: Make new sowings of warm-season vegetables after harvesting early crops.


  • Weeks 1-4: Mulch blueberries with pine needles or sawdust.
  • Week 1: Don’t spray any fruits while in bloom. Refer to local Extension publications for fruit spray schedule.
  • Week 4: Prune unwanted shoots as they appear on fruit trees.


  • Weeks 1-4: Birds eat many insect pests. Attract them to your garden by providing good nesting habitats.
  • Weeks 2-4: Herbs planted in average soils need no extra fertilizer. Too much may reduce flavor and pungency at harvest.
  • Weeks 3-4: Take houseplants outdoors when nights will remain above 50 degrees. Most prefer only direct morning sun.
  • Weeks 3-4: Watch for fireflies on warm nights. Both adults and larvae are important predators. Collecting may reduce this benefit.
  • Weeks 3-4: Sink houseplants up to their rims in soil or mulch to conserve moisture. Fertilize regularly.


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University of Missouri Extension Master Gardener Program