Dandelions are a "flower" that competes very well with turfgrass. File photo.

The summer moves on and so does gardening. 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: What is the most effective organic method of eliminating dandelions in grass? We planted the grass last fall (removed old grass first) and the dandelions came up soon after. We did not have this problem with the pre-existing lawn. – Marion County

A: Your best option is to hand dig the dandelions and then reseed any bare areas with grass. Make sure to keep the lawn healthy and well-watered so it can outcompete any germinating weeds. 

There aren’t any organic herbicide sprays available that will only target the dandelions. These chemicals will also kill your grass and leave dead spots. And with their deep taproot, the dandelion is likely to survive and grow back, – Brooke Edmunds, OSU Extension horticulturist

Q: I have a problem with spreading weeds in the backyard. I have been digging them out by hand using a garden tool. I sprayed weed killer but it’s not really working. Is there any natural way to keep them from spreading all over the backyard. – Clackamas County

A: Your two weeds are spotted spurge in the first picture and pearlwort in the second picture. They are both very hard to get rid of since birds, wind and shoes spread their tiny seeds.

Here’s an article on weed management from OSU Extension. There are some helpful ideas in there.

Both plants are best dug by hand when small. Take a clump of soil with the roots to avoid leaving rootlets in the soil. If you stay on top of clearing them, the population should decline over time, but especially get them when they are small so they don’t go to seed.

A weed killer with 2,4-D, dicamba, MCPP, and/or fluroxypyr will work on the spurge. Be sure to read and follow the directions carefully for best control.

Unfortunately, small pearlwort seedlings already have root systems large enough to escape the effects of herbicides. Apply preemergence herbicides prior to pearlwort emergence, or thoroughly hand weed pearlwort from containers prior to applying pre-emergent herbicides. Because pearlwort thrives in over irrigated areas, closely monitoring irrigation practices can be one of the best control measures.

Q: In last Saturday’s column, the question dealt with removing trumpet vine. The Master Gardener talked about the physical approach – digging, cutting, starving it out. Then she recommended Roundup. It is generally agreed that this product shouldn’t even be available in stores. I was so sorry to see this recommendation in the column. Coming from a Master Gardener, there is the aura of credibility. Sadly, I think this was a big oversight. Any chance you could address this in a follow-up column? – Multnomah County

A: Thank you for your careful reading and concern about the answer to what I assume was the trumpet vine question in this Oregonian column. If you were referring to another newspaper column, please let me know which one you were referencing.

To clarify the focus of the Extension Master Gardener Program: When we answer gardening questions, our goal is to educate gardeners about the options available to them, with a focus on sustainable gardening. We like to say that we are descriptive, not prescriptive. We help folks understand their options, so that they can choose which approach will work best for their situation. With a vigorous weed like trumpet vine, physical removal can be an effective approach, and I was happy to see that this was the first option given. However, physical removal takes a lot of time, physical labor and sometimes money – something that may or may not work well for this particular gardener.

The second option provided was glyphosate, which is an over-the-counter weed management option to gardeners across the state. The Master Gardener volunteer who answered the question made sure to provide information to limit the damaging effects of glyphosate to other plants, and to maximize effectiveness (thus limiting the need for additional applications) by specifying the timing. Although glyphosate may not be an option that you would personally choose, it may be a preferable option to someone unable to manage the physical removal of the trumpet vine. 

OSU Extension has no position, pro or con, on glyphosate. As the state’s land grant university, we work to educate others about their options and not legislate what they should do. In keeping with this approach, two OSU educators have written an article, in response to frequently received questions about glyphosate. In case you are interested in this information, I have linked it here. – Gail Langellotto, horticulture professor and Extension Master Gardener statewide coordinator

Q: Will great golden digger wasps dig through filter or landscape fabric? I’ve been asked to find a way to break an annual cycle of hundreds of great golden wasps setting up their nurseries in two xeriscape rooftop gardens in Corvallis. Since they are more alarming than dangerous, I’d like to be able to “sell” deterrence rather than eradication. Do you think waiting for the adults to emerge and then very quickly put down a fabric barrier and mulch before another round full-on excavation begins would be effective?

I read that the wasps prefer to create nests in dry, loose soil – the exact conditions currently in the courtyards. If the property managers were to provide irrigation to the areas during the busy weeks, would that likely change soil conditions enough to encourage the females to hunt elsewhere for nursery sites? If that were the case, we could delay installing the fabric and mulch to prevent future excavations.

The property managers are in a little bit of sticky situation – I am impressed that they are even willing to entertain least toxic measures given. – Linn County

A: No, they will not be inclined to burrow through landscape fabric. Yes, if you catch the emergence, you can put down the fabric. No doubt the emergence is staggered so some will be trapped underneath. That could not be helped.

Changing the soil environment could easily work and make the area less suitable for habitation. The property managers might have water restrictions, but you could always try.

Have you seen this information from Galveston County Master Gardeners on the Great Golden Digger Wasps? Your clients might be inclined to ignore them or at least be less panicky about them with more knowledge. Some people take great pride in knowing unusual things that can help “save the pollinators”.

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