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Helen Chesnut's Garden Notes: Coffee grounds a source of nitrogen for plants that like acidic soil

I have a longstanding habit of saving used coffee grounds and scattering them thinly around and under the blueberries, rhododendrons and other shrubs that prefer an acidic soil

Dear Helen: Our two prune plum trees have produced plenty of plums for years, until this year. Their usual abundance of spring bloom produced no fruit at all. Is there an explanation? Are we the only people with this problem? H.R.

I actually haven’t heard of anyone having a good prune plum crop this year. I’ve been asked your question many times over the summer. My own prune plum tree, which for decades has fed the neighbourhood and my circle of friends as well as myself, produced five poorly developed plums.

When these plum trees were blooming early in the spring, the weather over the entire bloom time was cold, wet and windy. At the time I wondered whether any pollination could be happening. In such prolonged adverse weather, bees and other pollinators had little chance to do their usual good work of moving from flower to flower, pollinating the blooms as they go.

Cold temperatures and wet conditions also affect the quality of the pollen and its ability to move smoothly to the centre of the flower to complete the pollination process.

Dear Helen: In a coffee shop recently I overheard a conversation about using coffee grounds in the garden. Are you aware of this practice?


I have a longstanding habit of saving used coffee grounds, letting them dry out a little, and scattering them thinly around and under the blueberries, rhododendrons and other shrubs that prefer an acidic soil. The coffee grounds are acidic. They are also a source of nitrogen for the plants.

A recent email from a reader told of using the grounds as a scented repellent to deter raccoons from blueberry bushes. It had never occurred to me that the scent might deter pests or predators.

Because coffee grounds tend to cake over in water-repellent mode, and become mouldy when laid thickly on the ground, it is always best to scatter them thinly or scratch them into the soil. Coffee grounds are an excellent addition to compost heaps as well.

Dear Helen: In an extensive container garden on my deck. I have thriving compact rhododendrons, and even blueberries. My problem: a very healthy hydrangea is producing flower clusters that are a muddy pinkish-purple instead of the vivid blue they are supposed to be. Is there anything I can do to begin returning the blooms to the colour I want?


Substances that will acidify the soil will turn the flowers blue. Most commonly recommended is aluminum sulphate, but powdered sulphur could also be sprinkled on the soil and scratched in to begin the acidification process. Apply the sulphur away from the plant’s stems and closer to the pot rim.

Other acidic materials, such as used coffee grounds, can be scratched in to the soil in modest amounts at a time to help acidify the soil.

If you fertilize your rhododendrons with a product specifically for acid-loving flowering plants (rhododendrons, azaleas, camellias), use that, but apply it to container plants more sparingly than is recommended for plants growing in open garden areas.

Weekend column. I’ll be taking time off from writing a column for the upcoming holiday weekend. See you back here next Wednesday.


Abkhazi Garden art show. Abkhazi Garden, 1964 Fairfield Rd. in Victoria, will be displaying painting and sketches inspired by the garden and created by local artists from Monday, Sept. 5, to Oct. 10. On Labour day, weather permitting, artists will be in attendance with their artwork displayed in the garden. The garden is open seven days a week from 11 a.m. to 4 p.m.

VHS meeting. The Victoria Horticultural Society will meet on Tuesday, Sept. 6, from 7 to 8:30 p.m. in the Garth Homer Centre, 813 Darwin Ave. Andy MacKinnon, co-author of the Royal BC Museum guidebook Mushrooms of British Columbia, will speak about mushrooms and fungi. Masks are required in the Garth Homer Centre. Non-member drop-in fee $5. For more information, visit

Floral arts. The Mid Island Floral Art Club will meet on Thursday, Sept. 8, at 2 p.m. in St. Stephen’s Church, 250 Village Way in Qualicum Beach. Theme of the afternoon is “Remembering Lynn Bonner, featuring designs made using her estate containers. New members are welcome. Guest fee $6.

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