Gardening season is underway, and you may have questions. For answers, turn to Ask an Expert, an online question-and-answer tool from Oregon State University’s Extension Service. OSU Extension faculty and Master Gardeners reply to queries within two business days, usually less. To ask a question, simply go to the OSU Extension website, type it in and include the county where you live. Here are some questions asked by other gardeners. What’s yours?
Q: My roses need help. They didn’t get trimmed back this spring. At spring break, they looked fine. But it kept raining and raining and raining. Can roses drown? I have 35 roses. Pretty much all of them have black spot and most of the leaves have dropped. I’ve given them rose food in the spring. Can you recommend a bee safe systemic food and spray – Linn County
A: There are a couple of fungicides that will help the roses, both a sulfur spray and/or pure Neem oil (purchase online). If the roses are completely covered with black spot, it may be a good idea to cut them back. I would not do a hard cut. By that, I mean not leaving only a few inches of canes on each plant. But I would cut back all dead canes and/or canes that are yellowing. Cut back at least an inch into the good cane material making sure there is no disease in the cane.
Clean up the area around the roses, getting all the infected leaves and canes and put in the garbage, not a compost pile. This fungus will survive in compost unless it is very hot. It will also survive during the winter in the soil. Make sure the center of each plant is open and has good airflow.
Your roses need organic material. Put a manure-based compost around each rose at least 2-3 inches thick and about 5-6 inches wide. After you cut the canes back, use either one of the sprays, follow the directions on the labels. Wear protective clothing, safety glasses and gloves. The sulfur can irritate your skin and burn your eyes. Neem seems to be pretty tame or non-irritating to most people. You need one good spray and then feed the roses a liquid fertilizer (fish emulsion, seaweed or kelp in a solution).
Again, follow the directions on the label. If you cannot get to the pruning right away, feed the roses the liquid fish emulsion.
Watch the development of the leaves, if you see the fungus again, spray making sure you get both the upper and bottom of the leaves.
Here and here are two links from Oregon State University on roses. – Sheryl Casteen, OSU Extension Master Gardener
BlueberryOSU Extension Service
Q: We moved into our house and are surprised all the time by things just coming out of the ground. It has been fun. However, we seem to have a blueberry bush/plant. We don’t know if it edible for us, pets, etc.? Can you help? – Marion County
A: Lucky you! You’ve got a mature blueberry bush loaded with tasty fruit.
Here’s an in-depth publication that has tons of information on how to care for your new plant. Tips for spring pruning are in there, too. It’s called Growing Blueberries in Your Home Garden and available in the OSU Extension publications catalog. There are many blueberry cultivars so it’s hard to tell which one this is exactly. Here is a list of common cultivars sold in Oregon: Blueberry Cultivars for the Pacific Northwest. You might be able to get close by comparing the characteristics listed in the “bush” and “berry” columns to your plant. – Brooke Edmunds, OSU Extension horticulturist
ManrootOSU Extension Service
Q: We discovered a vine growing in our shrubs. It has these large “fruits” and when we cut it open, it has large, lightweight seeds. We have no idea where this came from or what it is. We tried doing a Google image search and other searches and can’t identify the plant. Can you help? – Benton County
A: Lots of people wonder about this one! It is Marah oreganus, coast manroot, commonly called wild cucumber for obvious reasons. It is a common vine in western Oregon. It is not edible. Here’s a link to more information. – Signe Danler, OSU Extension online instructor
Q: Do UV light zappers attract and kill mosquitos? – Washington County
A: I’m not a fan of UV traps because of all the beneficial insects they kill. It turns out mosquitos are not attracted to UV light alone, but it is used to enhance the heat and carbon dioxide in a mosquito trap.
I’m attaching an article about mosquito traps, but the best solution is prevention by not letting water stand in things around your yard like buckets, pools and tire swings. We keep goldfish in our small pond to eat the larvae and that seems to work well for our standing water. Mosquito repellent is also effective if worn diligently. It’s been a wet year with lots of pools of water, so good luck. – Rhonda Frick-Wright, OSU Extension Master Gardener
Tulip bulbs. File photo.
Q: I work at bark/mulch company. I have lots of customers that discuss the depth of bark. More recently I have a co-worker that is saying that bulbs are affected by the depth of bark and when applied over bulbs it should not be over two inches. Is this true. – Clackamas County
A: As to depth of bulbs, the rule of thumb is to plant the bulb three times the height of the bulb (a 2-inch bulb would be planted 6 inches deep, etc.). Bark does not hinder the emergence of the bulbs, but it also doesn’t add nutrients that the bulb needs to grow roots.
The general recommendation seems to be 2-3 inches of mulch over bulbs, but of course if it was a small bulb like crocus that you only plant 3 inches deep, even 2 inches might be too much. So you see there is no hard and fast rule.
Your co-worker may just be trying to simplify life by saying 2 inches maximum, but it really depends on what kind of bulb is being planted. The point of mulch over bulbs is to keep them cool and moist in the summer, from freezing in the winter and weeds down in the spring. I hope this answers your question, and if they want to use 2 inches as a recommendation, it’s probably a good compromise. – Rhonda Frick-Wright, OSU Extension Master Gardener
