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: I’m seeing more and more clover every time I look at my front lawn. I don’t want to use anything that isn’t organic on the lawn. It sounds like clover is a sign of low nitrogen levels.
I’ve found some information about clover here and on other sites and it’s left me even more confused. Should I add fertilizer (and if so, what type)? Or should I pull up the clover and put down grass seed in its place? Or just ignore the clover and accept it as inevitable? – Clackamas County
A: Weeds generally enter lawns when opportunities arise, meaning when the turf canopy thins out from lack of nitrogen, poor or infrequent mowing, disease or insect damage, lack of water, and seeds getting blown in from areas surrounding your property or from ornamental beds. Once weeds get established, they can spread more quickly because of proximity to your lawn. Clover is no different in terms of entering your lawn but it has the added benefit of being able to fix nitrogen from the atmosphere and it grows laterally. Also, it produces seeds at low heights often under your mowing height so the seed heads do not always get mowed off.
Because of these reasons, once clover gets into your lawn, it can spread rapidly, especially if your lawn is not being fertilized. So, to say, “clover is a sign of an underfertilized lawn” is both partially true and also false. It is true that clover will spread faster in an under fertilized lawn, but it is not true necessarily that clover got there because of an under-fertilized lawn. It took the clover to blow in and find a starting spot, and other weeds could have done the same thing.
Interestingly, clover is often included in “Eco-lawn” mixes because, once it is evenly dispersed throughout your lawn, it provides nitrogen to your lawn so you may not have to fertilize your lawn at all (or certainly less), depending on the grass species present.
What you do with the clover is an entirely personal choice. I would fertilize your lawn if it is not dense and healthy. It doesn’t need to be lush green, but some fertilizer can do wonders for improving lawn quality, which will do a much better job of keeping weeds out. However, fertilizer will never remove the weeds that are present. All fertilizers work this time of year. For slow-release fertilizers, use either organic or methylene urea-based products. Polymer coated urea (PCU) products can work well, too. Soluble products can work, but you need to apply them at about half the rate as slow-release products and twice as often or else you get excessive growth spurts. However, when soil temperatures are cold, you need to stick to either soluble fertilizers like urea or ammonium sulfate or a slow-release fertilizer with polymer-coated, sulfur-coated urea (PCSCU). Because the temperatures are lower, you don’t get the big growth spurts.
You will likely have a difficult time finding PCSCU in retail stores and would need to find it online somewhere through a professional site (e.g. Wilbur Ellis, Target Professional Products, Simplot, etc.), in other words, a company that sells to golf courses, parks, schools and landscape maintenance companies. Organic and polymer-coated urea fertilizer products do not release well in cold weather.
– Brian McDonald, OSU Extension turf specialist
Q: We planted some trees and shrubs at our new house. We watered by hand last year. This spring we finished installing a drip system and we are watering in the morning for one hour daily. Is this OK? The trees are waking up, some slowly but with green stems and some new leaves. We are planning a trip to the Alaska highway in June. Should we leave our watering schedule the same? – Deschutes County
A: I can understand your concern about your newly planted landscape. You’re off to a good start with early morning watering. I would suggest you deep water every three to four days instead of daily watering. The soil should be saturated to 10 inches or more. It’s hard to say if you would need more frequent watering while you are away. It really depends on the weather conditions, which can fluctuate wildly year to year. – Christi Jones, OSU Extension Master Gardener
Plum with shot hole diseaseOSU Extension Service
Q: I have a plum tree that based on my research online has shot hole disease. The tree is semi-dwarf and 7-8 years old. It has a lot of young fruit this year, the most it’s ever had. I’ve notice that almost all of the leaves have the spotting that looks like shot hole disease. The advice I’m seeing says that I can’t really treat it except by cutting branches, taking off leaves, etc. What do you recommend? – Multnomah County
A: It just so happens that I have a tree just like yours. I have had this issue for three years. I did not take any leaves off. I do spray with organic fungicides like neem and a sulfur/lime mix. It has not gone away, but it doesn’t get worse either and the tree is growing.
Clean up the area around the tree, take off any low, low branches if you have them, and always water the soil, not the tree.
However, that said, with all the rain we have had it is impossible to keep the leaves dry right now. Both neem (that is pure neem with nothing added to it that you can purchase online), sulfur sprays and even the bicarbonate sprays will take the fungus down a notch. You can alternate sprays using sulfur then wait 10 days minimum and use neem or the bicarbonate spray. Both sulfur and bicarbonate sprays can be purchased locally already mixed. Look for a OMRI label on the bottle, which means the testing labs have seen it and it is okay for organic sprays.
Spray the undersides of the leaves as well as the tops and the whole tree. When spraying make sure it is a windless, dry day over 40 degrees and under 80 degrees. You want the tree to dry out completely afterwards so spray on a “no rain” day/night.
Always read the instructions and follow them. Overdosing the sprayer with neem will clog it and clog the leaves. Too much of any fungicide can kill the tree. Please wear protective gear and glasses. Sulfur can burn, neem doesn’t do much on human skin but you could be allergic to it. Remove fallen leaves, do not put them in the compost pile. – Sheryl Casteen
GinkgoOSU Extension Service
Q: My young ginkgo tree has suddenly developed brown dry outer edges on all its leaves. It was looking great just a few weeks ago. Any suggestions to save it? – Lane County
A: Ginkgo trees are known for their showy fan-shaped leaves. They are considered a “living fossil” and date back to the Jurassic period. Ginkgos are slow growing and do best when planted in full sun and well-drained, moist soil. They are known to be resistant to most disease and pest problems. The fact that your gingko suddenly developed a problem uniformly over the entire plant indicates that this is most likely not a disease or pest issue.
Brown and dry outer edges of your gingko indicate this may be a watering issue. Overwatering issues causes leaves to wilt and turn yellow with brown tips. Overwatering also causes the roots to turn brownish and begin to rot. Underwatering causes the leaves to become dry with brown tips, which is how you described the leaves of your gingko tree. If underwatering continues the leaves will begin to curl, wilt and eventually drop from the tree.
One other factor to consider is when you last fertilized your tree and how much you used. Over fertilization can cause damage to the roots, causing the roots to not properly absorb water. If this occurs, the leaf edges will begin to look brown and dried. If your plant is also underwatered, this will only intensify the effects of fertilizer on the plant and its roots. It is difficult to reverse overfertilization, but watering can help to leach out it out of the soil. – Jan Gano, OSU Extension Master Gardener
What’s eating this strawberry?OSU Extension Service
Q: I have been getting worms in and on my strawberries. What can I do to prevent this or get rid of the current ones? – Polk County
A: The worms could be the larvae of a fly. However, it is also possible that the hole was made by a different pest and the larvae were then laid in the fruit. If eggs are actually being deposited on undamaged fruit, pest management will need to focus on preventing adult flies from accessing the fruit.
Laying a summer-weight floating row cover fabric over the ripening fruit may be one strategy; however, if the fruit is covered too early, pollination may not be complete, and the fruit will not form properly.
Pick ripe fruits daily and promptly remove any damaged or rotting fruit. These should be buried or sealed in a trash bag since the flies are attracted to the smell of fermenting fruit. – Lynne Marie Sullivan, OSU Extension Master Gardener
