Ornamental Garden Calendar For July

Trees and Shrubs

  • July traditionally is a drier month and a good time to prune evergreens like boxwood.
  • Continue to watch your lilacs, flowering crabapples, ninebark and currant bushes for signs of powdery mildew. If it has been a problem in past spray with a solution of 1 Tablespoon of baking soda and 1 Tablespoon of horticultural oil mixed in 1 gallon of water or diluted butter milk- 1 part butter milk to 10 parts water. Begin spraying before the mildew forms and every 2 weeks after. Maintain even soil moisture and try to avoid overhead watering. 
  • Begin protective fungicide sprays for junipers and eastern red cedar. Begin spraying in July every 10-14 days until the end of August. This protects against apple cedar rust.
  • Adult boxwood psyllids are still flying around this month and are laying their eggs. They can be sprayed with an insecticidal soap to help reduce next year’s population. Continue to prune out the cupped leaves.
  • Continue to monitor purple-leaved sand cherries and fruit trees for European fruit lecanium scale, eggs may still be hatching. Remove any found and/or spray crawlers with insecticidal soap.
  • Continue monitoring for crown gall and galls on susceptible trees and shrubs.
  • During the hot dry days in July and August prune out any dead or diseased twigs from junipers infected with either phomopsis blight or kabatina blight. Clean your blades between cuts and burn or black bad the clippings.
  • Adult Viburnum leaf beetles begin emerging from the soil this month, mating and laying their eggs inside young branches. Hand pick them by knocking them into a dish of warm soapy water. Like Japanese beetles they drop to the ground when disturbed so hold your bowl under them.
  • Pine bark adelgid crawlers may be making an appearance on pines this month. Look for the white cottony wax that coats the adult females and clings to the bark on trunks, branches and at the base of needles. Crawlers may be sprayed with an insecticidal soap, wiped off or blasted with a strong jet of water.
  • Honey lotus plant bugs are laying their eggs in the bark this month. If you are spraying for them do so before they lay their eggs.
  • Give wisteria vines a very hard pruning in the back half of the month or the beginning of August. Prune to maintain desired size, shape and to thin out overcrowded stems completely.
  • Keep your dogwood shrubs adequately hydrated this month and monitor them for insect infestations such as scale, bores, sawflies, aphids and club-gall midge and control any found. Both efforts will help to reduce the risk of Botryosphaeria canker.
  • If you live in areas affected by box tree moth pheromone traps can be set up to catch the male moths the first half of the month. By about mid-July begin scouting your boxwoods for signs of the larvae which will be feeding mid-July to mid-August. Treat with BTK if infected.


  • Be on the lookout for signs of powdery mildew on susceptible plants like phlox, roses, asters, coreopsis, delphinium, lungwort, monarda, centaurea and peonies. Avoid overhead watering where possible and maintain even soil moisture. 
  • Prune climbing roses and rambler roses after bloom.
  • Divide bearded iris now.
  • Stop pinching back mums this month.
  • Once daylilies have finished blooming, they may be cut back to the ground if they are diseased or scorched. 
  • Aphids can be a real nuisance this month if there is ample moisture and moderate temperatures. Scout the growing tips, especially flowers, for their presence and squish them, blast them with water, prune them off or spray with an insecticidal soap. Ease up on fertilizers to reduce the succulent new growth that attracts them.
  • The bristly roseslug sawfly is still active watch for them on your roses.
  • Protect the leaves of your daylily plants this month from leaf scorch by keeping plants adequately watered. Be on the lookout for Daylily leaf streak (a fungal disease) and remove infected leaves to slow the spread.
  • Continue dead heading flowers for a continuous bloom. Some of the plants that require dead heading are: Coreopsis, Coral bells, Daylilies, Blanket flowers, Maltese cross, Daisies, Pinks (Dianthus), Columbines, Butterfly weed, Delphiniums, Globe flowers, Buttercups, Pincushions, Gas plants, Golden marguerites, Campanula Bellflowers, Salvia, Yarrow, Spider wort, Centaurea, Lady’s mantle, chives and Foxgloves.
  • Remove Columbine leaves infected with leaf-miners and destroy them.
  • Lavender plants may be lightly pruned back after flowering to encourage a second, but less abundant bloom.
  • Be on the lookout for peony blotch and remove infected leaves and black bag them.
  • If growing Impatiens continue to be on the lookout for downy mildew and remove any infected plants and black bag them. Replant with something different.
  • Taller varieties of sedum (like autumn joy) may be cut back in half if they have grown to tall. To grow shorter plants that do not flop reduce their water.


  • Be on the lookout for powdery mildew on zinnias, begonias, snapdragons and verbena. Avoid overhead watering where possible and maintain even soil moisture. 
  • Deadhead Geraniums, Dahlias, Heliotrope, Zinnias, Marigolds, Pansies, Snap dragons, Verbena, Lantana, Petunias and Cosmos to keep them blooming.
  • Continue to pinch back Basil, Tarragon and Coleus.
  • Cut back petunias by 1/4 to 1/2 of its growth to keep them from getting leggy.


  • Weeds traditionally here in southern Ontario begin to slow down during our summer heat. Where they are well watered though they will still be abundant. Keep up to the weeding and do not let anything go to seed. Weeds in bloom this month Black medick, Lambsquarter, Common mallow, Carpetweed, Redroot pigweed, Prostrate knotweed, Purslane, Prostrate spurge, Spotted Spurge, Common Vervain, Ox-eye daisy, white clover, Chicory, Pineapple weed, Queen Anne’s lace, Curled dock, Heal-all, Milk thistle, Bindweed.


  • Chinch bugs can be a real problem this month. Hot dry conditions are ideal for them. Increase your watering if you are experiencing chinch damage. Insecticidal soap sprays or neem oil sprays may be useful.
  • Pull back on fertilizing over the hot summer months.
  • Keep lawns mowed high to reduce scorching. 3 to 3 1/2 ” is a good mowing height.


  • Japanese beetles make their appearance in July. Hand pick them by knocking them into a dish of warm soapy water. Japanese beetles drop to the ground when disturbed so hold your bowl under them. If you are using a pheromone trap for them, be sure to place it at least 9meters (30′) away of vulnerable plants further if possible. If you are on an acreage or large property 76 meters (250′) is ideal. Place them in a non-flowering tree, like a pine or spruce about 4′ high. Note: these traps will lure about 4 times as many Japanese beetles to your yard then you would normally have; they trap about 75% of those lured…meaning you have not in the end really reduced their numbers.
  • Supplement rainwater with irrigation to ensure 1″ of water per week for established lawns, gardens, trees and shrubs.

Photo credits: all photos taken by the author.

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