May Zone 5

What to do in the garden in May in Zone 5

  • Fertilize trees, shrubs, perennials  Apply a balanced fertilizer to all your trees, shrubs and perennials if you have not done it yet.  Use liquid or a slow release granular.  Note:  Certain perennials, and shrubs for that matter, do not require fertilizer.  For all your plants, follow recommendations for the specific plant.
  • Feed annuals  Annuals need regular fertilizing for good bloom production, about every 4 weeks.
  • Apply broadleaf weed control  Apply broadleaf weed control in May.  Although you can purchase fertilizer with broad leaf weed control, conditions should be ideal when you apply (read the package) for best results.  Mixing up some weed-b-gone in a tank sprayer is more effective.  It also allows you to spot spray individual weeds are target small areas.  Clover and creeping charlie require several applications.  With a pump sprayer you can target those every few to several days.
  • Plant warm season vegetables  As soon as the soil warms up to about 60 degrees, tomatoes, peppers, etc. can be planted in the garden.  Beans can be direct sown.
  • Transplant  Move shrubs and trees after the soil thaws out and dries up if it hasn’t been done already, before new growth begins, and the weather is cool.  Transplant shock will be minimized.
  • Plant container grown shrubs, roses and trees  Container grown trees, evergreens and shrubs can be planted.
  • Plant perennial seeds  Seed can be sown for just about anything now.  The seeds that need warm soil should germinate easily now.
  • Stake plants  Stake tall plants that need support and protection from wind before they get to tall to confine.
  • Mulch  Apply 2-4 inches of mulch to perennial beds and trees if you haven’t done it yet.  Thick mulch will inhibit weeds and help keep the soil moist.
  • Transplant seedlings  Transplant any annual, perennial or vegetable seedlings into the garden beds if you haven’t done it yet.  Complete the hardening off process first and protect from late frosts.
  • Mow  Get on a regular mowing schedule.  You should not be removing more than 1/3 the length when you mow.
  • Deadhead  Remove spent blooms from early flowering shrubs and shrub roses.  Deadheading will improve the appearance of the shrub and encourage faster re-bloom.  Rhododendrons should be pruned as soon as flowering is complete.  Deadhead the spring flowering bulbs if you haven’t yet, but don’t cut back the foliage until it is yellowed and withered.
  • Spray or dig weeds  Weed season is well underway in May, and it is best to control them before they get well established.  Dig weedswhen the soil is moist to help remove the entire root system.  Many weeds will re-grow from the tiniest bits of root left behind, especially dandelions.  If not opposed to chemicals, apply liquid selective weed control, such as Weed-B-gone, to lawn weeds.  A pint size spray bottle allows you to minimize the chemicals used by applying only to individual weeds.  Be especially cautious of drift to perennials, shrubs and trees.  The slightest wind can carry the spray a long way, damaging foliage.  Non-selective weed control sprays, such as Round-up, will kill every plant it comes in contact with.  Never use weed chemicals in garden beds, the risk of killing plants is too great.  Pull or dig them when the soil is moist, or regularly hoe the soil to pull up weed seedlings that are not well established.  Weeds in the gardens will use up moisture and nutrients that your plants need.
  • Fertilize early bloomers  Early blooming shrubs may need feeding after the first flush of blooms.  Rhododendrons and Azaleas will need an acid fertilizer now to keep the foliage from yellowing, or work cottonseed meal into the surrounding soil.  Each shrub and perennial has unique feeding requirements, be sure to follow maintenance recommendations for each plant.
  • Shape hedges  After a flush of summer growth, shaped and pruned hedges should be trimmed, usually in May.
  • Pinch  Pinch back annuals to promote fuller growth.  Petunias and zinnias in particular will benefit from pinching back when the have reached about 4-6 inches.
  • Water  Water all newly planted shrubs and trees deeply every 7-10 days while the roots are establishing.  Established trees should get a deep soaking as summer heat sets in.
  • Fill the birdbath  Fill shallow birdbaths frequently.  Deep birdbaths can harbor mosquito larvae so empty stale water and refill.
  • Take down the coldframe  By the middle of May you can put away the coldframe.
  • Apply organic fertilizers  Now that the soil is warm enough to activate microbes, compost, manure, fish emulsions and blood and bone meal may be applied in the gardens.


  • Check containers and baskets  Container gardens, hanging baskets and window boxes dry out quickly and need frequent watering.  They will also need to be fertilized regularly.
  • Heat up the compost  If the compost isn’t ready yet but is not heating up, add green plant material such as grass clippings or fruit and vegetable waste, or add a shovel full of manure.
  • Check for insects  Keep an eye on your plants for insects that may be causing damage.  Do not indiscriminately spray insects, as many are beneficial.  Even those that cause visual damage may not necessarily be harming the plant.  Check with your local garden center or extension service to properly identify and treat for insects.  Routinely spraying them off with a garden hose or applying insecticidal soap is often the best course of action.  Or use a water bottle with a small holed tip on it that will produce a strong stream.  Aphids is a common problem.  Although they generally do not do permanent damage, they can inhibit growth and weaken the plant.
  • Check for disease  Keep an eye on your plants for signs of disease such as wilting, leaf drop, and discolored foliage. Check with your local garden center or extension service to properly identify plant disease and treatment.  It is tempting to water and fertilize if a plant appears weak or diseased, but until the problem is identified it is best to withhold both water and fertilizer.  Many diseases are caused by or accelerated by over watering and poor drainage.  Keep watering to a bare minimum until the problem is identified.
  • Check for slugs  June is sometimes a rainy month and will encourage slugs.  If slugs have eaten holes in the foliage of your shade plants such as hosta, pick out the slugs and dispose of them or apply non-toxic Sluggo.
  • Evaluate  Make notes in your garden journal frequently.  Record how each plant is doing and the time of year and weather conditions.  Note whether soil seems to dry out too quickly or hold water too long so you can amend the soil next season.  Note areas that are being shaded more by growing trees so you can move perennials as necessary next season.
  • Drink water and wear sunscreen!
calendarSharon Dwyer