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Horticulture News and Tips

(A monthly horticulture column from the CF NEWS)


If you enjoy spring flowering trees (and who doesn't) then May must be your month. One of my favorite May flowering trees happens to be a small native named Prunus virginiana 'Schubert'. Commonly known as chokecherry it has an open oval crown and covers itself with 3" to 6" long racemes of sweetly fragrant white flowers that bloom alongside the finely serrated 2" to 4" oval green leaves. It gently billows in a spring breeze releasing its delicious fragrance. The overall effect is stunning and quite pleasing to the senses. When done blooming the flowers are followed by pea sized dark purple fruits that the birds just love. Not a single drupe will remain on my tree by midsummer. If this wasn't enough of a reason to love this tree the show continues on slowly and by midsummer the leaves have changed from green to dark purple. If you didn't notice the gradual change you would think it was a different tree. Not too large, easy to grow in zones 2-7, beautiful fragrant flowers, a changing leaf show and fruit loved by wildlife what more could you ask for in a native tree? Well, unfortunately Prunus virginiana like other stone fruit trees are susceptible to disease.

Black Knot is one such disease that is rapidly becoming a major problem affecting trees in the Prunus family.

Black Knot Disease is caused by the fungus Plowrightia Morbosa (Apiosporina). It is easily identifiable by the long blackish swollen unsightly galls or knots that form along the length of stems and branches and even on the trunks of affected trees. The gall will encircle the branch and may cause the part of the branch beyond the gall to die. If the branch lives the gall will continue to grow and will continue to release spores every spring. It is during wet periods in the spring that the galls or knots expel spores that will infect young shoots or wounded branches causing more galls to form. If left untreated the tree will become highly stressed and very unattractive.

Since Black Knot does not systemically affect a tree the best way to treat this disease is to prune out the infected branch. Remove at least 4" of healthy wood ahead of the gall. You will have to be vigilant in this as it may take several years to completely remove all infections as young galls are easily overlooked. Once removed burn, bury or dispose all branches from the site as spores can still be produced on pruned branches and spread to new areas. I have read that fungicides can help but I'd recommend contacting your local extension office to see what could be safely used in your area.

Sadly, my 'Schubert' is afflicted with this disease so every spring for the last few years we prune out all of the visible knots. I am not sure if we bought it with this disease or if it contracted it when I brought it home. Once I became aware of the disease I noticed a stand of wild chokecherries about two miles away that are infected. It is important to try not to spread this disease and had I known at the time I would have purchased a different flowering tree. But for now I'll keep pruning galls. It's such a pretty little native that I won't give up on it unless I see the problem has spread beyond my tree.

Liz Rinaldi, Horticulture Chair.


"In the Garden"
(Monthly horticulture tips for gardeners)


  • Time to plant the vegetable garden
  • Tend and enjoy your roses!
  • Use organic fertilizer
  • Use watering can so foliage won't get wet
  • Remove leaves with fungus or black spot immediately
  • Plant garlic, chives and rue near to ward off Japanese beetles
  • Stake tall perennials


  • Stake tomatoes and beans
  • Tend newly planted perennials


  • Decide the plants you have enjoyed
  • Tie a colored ribbon around ones you'd like to give another home
  • Stop deadheading plants with good seed heads for the birds to feed on in winter


  • Put down compost and/or organic fertilizer
  • Take cuttings of impatiens, coleus or begonias for flowers in your home all winter
  • Prepare houseplants to bring inside
  • Do this when outside & inside temperatures are the same
  • Check and spray for insects
  • Select bulbs for fall planting


Copyright © The Federated Garden Clubs of Connecticut, Inc.
Last updated
April 28, 2017