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Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Failure to fruit, Vaccinium, Plum, Prunus

We have three blueberry bushes of different varieties that have been bearing just fine over the last several years. This year one of them bloomed heavily and looks like it's generating a good crop. The other two only had a few flowers. What could account for this? Is there anything we should be doing to encourage blooming and fruiting?

I am also wondering when we will ever see fruit on the Italian Prune tree I planted several years ago. It was already pretty big when we bought it, and now it is about 2 inches caliper near the base and is about 12 feet tall. Is there anything we can do to encourage some fruit on this? I do not even remember seeing it bloom this year. Could it have something to do with the weather patterns?


One problem might be a lack of bees. There could also be other reasons, such as Botrytis blossom blight, and blueberry shock virus.

Here is a page from Oregon State University which has some good general information on growing blueberries .

Is it possible that the blueberries have become dense and twiggy? If they are not pruned, they may become unproductive. The information below is from University of Florida Cooperative Extension:

Pruning mature blueberry plants is largely a matter of cane removal or cane thinning. The objective of pruning mature bushes is to stimulate the proper balance of vegetative and reproductive growth, and limit plant size. Pruning stimulates the development of new canes which are more productive than older canes. A general rule is to remove about 1/4 to 1/5 of the oldest canes each year (usually one to three of the oldest canes). This will result in continuous cane renewal so that no cane is more than three or four years old. Pruning to reduce the number of flower buds may also be required on some southern highbush cultivars which set heavy crops such as 'Misty'. Flowers should always be removed from one and two-year-old plants by pruning or rubbing them off before fruit set occurs. Most pruning is usually done immediately after harvest during the early summer. Removal of some of the flowers buds to adjust the crop load is usually done during the late winter just before growth begins.

As for the Italian prune, a plum tree may not begin to bear until it is 3 to 6 years old.

You may also want to visit a Master Gardener Clinic with your questions. You can locate a Master Gardener Clinic within King County on this website.

Date 2017-09-27
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Plant Answer Line Question

Keywords: Vaccinium, Planting

I planted some two- to three-year-old blueberry bushes about a year ago. I may not have transplanted them correctly. I did not loosen up the root system of each bush, did not shake out the soil mixture into which they were potted, and did not spread out the roots laterally within a two- to four-inch depth from the surface. Will my improper planting technique prevent these bushes from producing the gallons of berries that are in my dreams?

On the assumption that I need to pull them up and give them a better start, I have these questions:
Is this a good time of the year to pull them up?

Am I correct in loosening the root ball, shaking out the original potting mixture from the roots, and then spreading out the roots to a shallow depth?

Do you have any other tips for transplanting blueberries?


I wonder if the bushes have been healthy despite your not planting them exactly according to directions. You could wait and see how they perform this year, and then decide if you need to replant them. If you want to replant them in any case, the best time is in the early spring, after the soil has thawed but before bud break (in our climate, you may want to do this in very late winter).

According to The Berry Grower's Companion by Barbara Bowling (Timber Press, 2000), you should remove half of the canes of a mature blueberry bush at the base of the plant. Prune any remaining canes back to 3-4 feet high. Dig around the root ball, taking as big a root ball as possible. (If they look rootbound, then do gently loosen the dirt around the roots). Be sure to have your new planting hole prepared beforehand [...] the width of the hole should be sufficient to spread out the roots, and it should be deep enough to plant them at the same level they grew in originally. Make a bit of a mound in the middle of the hole and array the plant's roots over it, and fill in the hole. Tamp down the dirt gently, and water well. Once replanted, you can mulch around the plants with organic matter, such as grass clippings or straw.

Here is an article from Oregon State University entitled Growing Blueberries in the Home Garden which may be helpful.

Date 2018-03-15
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Plant Answer Line Question

Keywords: Vaccinium, Pollination

What flowering plants should I place near my two blueberry plants in containers on my driveway that might attract the kinds of insects to maximize pollination of the blueberry plants?


Almost any plant that flowers at the same time your blueberry plants flower will help attract pollinating insects. This could be anything from apples to clematis to more blueberries. The Xerces Society (a Portland-based conservation organization) has published this useful fact sheet about choosing plants to help our native bees.

Date 2018-03-14
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Plant Answer Line Question

Keywords: Vaccinium, Berries--Diseases and pests, Rubus, Fragaria, Insect pests, Prunus, Fruit--Diseases and pests, Berries

Could you tell me more about a new type of fruit fly that is supposedly infesting fruit here in the Pacific Northwest? Which fruit are affected?


The fruit fly is called the Spotted Wing Drosophila. It is known to affect strawberry, raspberry, blueberry, plum, peach, cherry, and grape. Oregon State University has created an information clearinghouse about this pest. Here is their information for home fruit growers. Washington State University has also devoted several web pages to this fly. Here is their Integrated Pest Management information, excerpted below (SWD stands for Spotted Wing Drosophila):
"Monitor for SWD using traps. [...] These vinegar traps are for monitoring purposes only and will not provide control of SWD. Remember, chemical control is not necessary if SWD is not present.
Composting fruit will likely not be effective at destroying maggots and pupae.
Remove infested and fallen fruit. Destroy or dispose of infested fruit in a sealed container.
Management recommendations are currently being developed for this pest. For the time being, good sanitation practices should be used."

Whatcom County Extension has clear, basic information for home gardeners as well. Since this insect is a relatively recent invader in the Northwest, information is constantly being adjusted and research is ongoing.

Date 2017-08-15
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Plant Answer Line Question

Keywords: Vaccinium, Organic fertilizers, Fertilizers

Is ammonium sulfate considered an organic fertilizer? I'd like to use some on my blueberries, but suspect it is not organic.


According to Fertilizers and Soil Amendments by Roy Hunter Follett (and others), ammonium sulfate is one of the oldest chemical fertilizers, and is "a frequent by-product of the steel industry, particularly the coking of coal." That doesn't sound like it meets organic guidelines. It is also tricky to use because it can cause phosphorus and aluminum to build up in the soil. The Organic Materials Review Institute lists it as a prohibited (for certified organic growers) synthetic crop fertilizer and soil amendment. You might do better using a slow-release certified organic fertilizer labeled for acid-loving plants. Cornell University Extension's publication, Production Guide for Organic Blueberries" mentions fish, soy, and alfalfa meal as organic-acceptable amendments.

Date 2017-07-18
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May 31 2018 13:14:08