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Year Round Gardening: May Garden Calendar

By: Eileen Tully, Colorado Master Gardener
April 30, 2016
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Average last frost date in town: May 10 to May 15

Early May

  • Clean and sharpen garden tools.
  • Change the oil in your lawnmower, sharpen the blade and replace the spark plug and air filter.
  • Lawn: apply fertilizer with high nitrogen content for a quick boost. Select one where the first number, representing nitrogen, is the highest. Products labeled as combined fertilizer and weed control are not recommended unless a significant and persistent weed problem is known to exist.  Always read the label carefully and completely when applying herbicides.   
  • Check your irrigation system to ensure its reaching all areas of your lawn and gardens.
  • Pruning of many evergreen and conifers starts now. If you want to control the shape of Mugo pines, pinch or cut out 2/3 the length of the new-growth “candles.”
  • Plant herbaceous perennials, raspberries, potted roses, container grown and balled and burlap trees and landscape shrubs. If you’re new to Colorado and not sure what will grow here, look for perennials marked “Plant Select” at your local nursery. These plants are grown for our region and will thrive in our challenging climate. Many of them will be labeled drought tolerant but all new plants will require water until they get established.

 

Mid-May

  • Thin seedlings of early planted crops such as carrots, lettuce, spinach and beets.
  • Stake peonies and delphinium.
  • Spring bulbs: remove the faded flowers after they have bloomed but don’t cut the leaves until they have yellowed because they provide energy for next year’s blooms. At that time the leaves and stems should easily pull out of the ground. If you plan on moving bulbs in the fall, mark where they are planted with colorful golf tees.
  • Starting now, feed roses a balanced rose food every six weeks during the growing season.
  • Check containers and prepare them for planting. If there was disease in any of them last year, don’t reuse last year’s soil. We recommend cleaning all containers with a solution of 1 part bleach to 10 parts water.
  • Depending on your location, start planting annuals. In many parts of Colorado Springs, mid-May is the time it’s safe to begin planting tender annuals.  But check the weather and your elevation! It’s not unusual to have a hard freeze in late May.
  • Begin planting gladiolus every two weeks through June for a continuous series of blooms.
  • If weather remains warm, transfer seedlings outside but harden them off in a sheltered location for a week before planting.

Late May

  • Transplant tomatoes setting the plants one inch deeper than in the pot.
  • Plant corn, bean, pumpkin, squash, cucumber, and early-maturing melon seeds now if the soil is warm.
  • Plant eggplant and pepper plants when the soil has reached at least 50 degrees.
  • Prune early spring-flowering trees and shrubs such as lilacs and forsythia after flowers fade.
  • Harvest asparagus stalks larger than 3/8 inch until about the end of June. Cut just at soil level.
  • Plant annual seeds outdoors the last week of May. Some suggested flowers are zinnias, salvia, sunflowers and nasturtiums. If you want to grow annual vines you might try Hyacinth Bean vine (Lablab purpureus), one of the Plant Select plants with striking purple flowers and deep purple seed pods. Another good choice is Cardinal Flower vine. Its trumpet-shaped flowers and feathery, deep green foliage attracts hummingbirds.

When you have questions, CSU Extension has research-based answers. Get answers to your horticultural questions by calling the Master Gardener Volunteer Help Desk at 520-7684 or submitting questions anytime at ask.extension.org

 

CSU Extension is located at 17 North Spruce, second floor Room 220

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