Ornamental Garden Calendar For June

June is my favorite month in the garden. So many perennials and flowering shrubs are blooming and the annuals are beginning to fill out a bit. The landscape is alive with colour and the air is full of a bouquet wonderful fragrances. The temperatures are warming up but but usually still remain comfortable. There is still a lot of work to do in the gardens in June so here is a list of some tips and tasks for the month of June. NOTE: the gardening calendar laid out here is based on Zone 6a in Southern Ontario. You may have to adjust your timing depending on where you are gardening.

Trees and Shrubs

  • Prune lilacs and other spring flowering trees and shrubs once the flowers begin to fade.
  • Dead head lilacs.
  • Candles can be pinched out on pine trees before they expand, if you wish to contain it’s size.
  • Sun scorch may be a problem on Japanese maples that are growing in full sun. Keep these trees well watered. If you have a real problem with this , year after year, you might want to consider relocating the tree (if it is not to big) in the fall or next spring.
  • Honey locust plant bugs active in June be on the look out for them and their damage.
  • Watch for bagworms feeding on many garden plants, but especially juniper and arborvitae. Hand pick or spray with BTK.
  • Begin monitoring your lilacs, flowering crabapples, ninebark and currant bushes for signs of powdery mildew. If it has been a problem in past protective treatments should be applied every 2 weeks. Homemade sprays containing baking soda are usually effective at preventing it from worsening. I use Cornell University Recipe.
  • Continue monitoring for crown galls on euonymus, lilac, willow, honeysuckle, weeping fig, poplar, apple, cherry, plum, apricot, chrysanthemums, asters, daisies, grape vines and brambles like raspberries. 
  • Continue monitoring for fungal galls on  forsythia, viburnum, highbush blueberry, American elm, hickory, maple, oak, and privet.
  • Continue watching for tip die back on junipers and continue protective fungicide treatments for Phomopsis blight, where warranted.
  • June is an excellent month to prune evergreens. Choose a nice dry day to prune and never prune wet foliage.
  • Boxwood leaf miners are mating in the beginning of June if  your boxwood shrubs are infected with them spray insecticidal soap spray at this time; preferably spray in morning when it is cooler and avoid spraying on hot days.
  • As the humidity kicks in monitor trees and shrubs for signs of fungal diseases. Try to avoid overhead watering that serves to keep the leaves wet to long, encouraging fungal diseases.
  • Gypsy moths are active this month be on the lookout for them and their damage. Spray BTK (Bacillus thuringiensis var. kurstaki) if populations warrant it.
  • Now is a good time to prune out any deadwood in your trees and shrubs that you may have missed during dormant pruning. 
  • Aphids and other soft bodied insects can become abundant this time of year, trees and shrubs may be sprayed with insecticidal soap if populations warrant it. Reduce fertilizing if they are abundant, as these insects are attracted to the lush new growth.
  • Viburnum leaf beetles begin reemerging from the soil to resume feeding and mate towards the end of June to mid-July be on the lookout for those. Hand pick and destroy.
  • Monitor apple trees for signs of rust or cankers and remove all diseased material.
  • Many species of Scale insects are actively feeding now. Remove insects by hand or use a cotton swab dipped in rubbing alcohol to wipe them off; a tooth brush also works.
  • Monitor Dogwood, Lilacs, Ash, Peach and Rhododendron for clearwing bore damage.
  • Monitor Green Ash, White and paper Birch, and young flowering Crabapples, Hawthorns and Maples for Flatheaded bore damage.
  • Cool season mites on evergreens are gearing down while warm season mites begin gearing up in June. Watch for stippled leaves and fine webbing, a sign of their presence. Use a summer oil spray or chemical  miticide. I use Cornell University recipe.
  • Keep string trimmer back from tree trunks and shrubs to prevent damage to their vascular system.

Perennials

  • If receiving adequate water perennials are typically growing very actively in June. Be sure to keep them well fertilized to provide nourishment for this new growth.
  • Lavender plants may be lightly pruned back after flowering to encourage a second, but less abundant bloom.
  • Leaf tiers are highly active this month on hydrangeas particularly ‘annabelle’ and ‘incrediball’. Remove affected leaves or pry the leaf open and squish the leaftier caterpillar.
  • Protect your daylilies from leaf scorch by keeping them well watered. They are especially vulnerable to scorch after a period of cloudy skies.
  • During wet periods or a lot of over head watering check daylily leaves for signs of daylily leaf streak and remove infected leaves.
  • Thin plants or reduce their size in order to maintain good air flow in the garden and reduce over crowding.
  • Be on the look out for thrips and leaf hoppers.
  • Deadhead bulbs and spring flowering perennials as blossoms fade.
  • Be on the lookout for vinca stem blight,
  • Be on the lookout for peony blotch.
  • Apply a balanced rose fertilizer after the first show of blooms is past and continue your preventative treatments for black spot.
  • Check the stems of your clematis regularly for reddish lesions on the stems and/or spotting on the leaves and stems, that could be an indication of clematis wilt disease. Prune back diseased vines to healthy wood and disinfect clippers after each cut.
  • Prune wisteria vines back after flowering is finished. Prune the entire vine, thinning it out well and leaving just one or two buds or nodes per branch (the branches grow off of the main stems). Get rid of any branches that hang down and spoil the shape of the plant. To force the plant to branch more horizontally, make your cuts on a down-facing bud. 
  • Continue checking roses for Roseslug Sawflies squish any you find.
  • Aphids and other soft bodied insects can become abundant this time of year, perennials may be sprayed with insecticidal soap if populations warrant it. Reduce fertilizing if they are abundant, as these insects are attracted to the lush new growth.
  • Deadhead salvia plants once flowers begin to fade for a second, less showy bloom later in the season.
  • Deadhead Bleeding hearts, 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, Yarrow, Spider wort, Centaurea, Lady’s mantle, chives and Foxgloves for a continuous display of flowers and/or to keep them from self seeding everywhere.
  • Iris bores are active this month be on the lookout for them and bacterial Soft Rot. Remove infected tubers and black bag them.
  • Remove Columbine leaves infected with leaf-miners and destroy them.

Annuals

  • Planting continues for annual flower displays. Be sure to water frequently in the beginning until they are well established as annuals from cell packs have a very small and shallow root. Using a root stimulator at the time of planting will help to speed up their establishment.
  • If possible water flowers from below rather than overhead watering to keep the leaves dry and help prevent disease. 
  • Deadhead Geraniums, Dahlias, Heliotrope, Zinnias, Marigolds, Pansies, Snap dragons, Verbena, Lantana, Petunias and Cosmos to keep them blooming.
  • Pinch back Basil, Tarragon, Coleus, Mums,  and Asters plants to create bushier and more compact growth.
  • If growing Impatiens be on the look out for downy mildew and remove any infected plants and black bag them. Replant with something different.

Weeds

  • Weeds continue to grow abundantly through June. Keep up to the weeding and do not let anything go to seed. Relief is on it’s way, weed growth typically slows down in July.
  • A few weeds in blooms the month of June include; Yellow rocket, Dam’s-rocket, Stinkweed, Common Purslane, White clover, Rough cinquefoil, Canada thistle, Sow thistle, Giant Hogweed, Cow parsnip, Wild parsnip, Sheppard’s purse, Tufted vetch, Sheep sorrel, Broad-leaved dock, Curled dock, Prostrate knotweed, Lady’s Thumb, Mouse-eared chickweed, Poke weed,  Poison Ivy. Keep these from going to seed to reduce future weeding.

Lawns

  • Water turf as needed to prevent drought stress.
  • Remove no more than 1/3 of the turfs height per mowing.
  • Begin raising your mowing height as the weather begins heating up. 3 to 3 1/2 ” is usually a good height (depending on the variety grown) this time of year.
  • Dandelions are in seed hand pick any being careful not to release the seed on your lawn. Merely mowing them down will give you a bumper crop in the fall. 
  • Grubs may still be feeding until near the end of June when they will stop and pupate in the soil.
  • Surface insects like chinch will begin actively feeding in late June through September. Ensure your lawn remains well watered to reduce their populations. Sprays for these insects may start being applied in June. 
  • Most over-seeding work should be wrapping up by now as it is difficult to germinate grass seed during the heat of summer.

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