Ask an expert: What can I do about my Spanish bluebell infestation?

Gardening season has started, 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 have a few clumps of Spanish bluebells infesting different parts of my yard, and read that they are invasive and pretty hard to get rid of.

Some people say dig up the bulbs, but this is hard because there are numerous baby bulbs that get away. Other advice says to pull the leaves/flowers out to starve the bulb. I even read advice that said to trample the leaves. Do you have any suggestions for how to get rid of these plants? – Multnomah County

A: I am in your shoes, too. I have a large patch of the bluebells.

One year I even bet my husband that his method of burning them would not be as effective as my method of frequently removing the tops with a hoe. It was a tie. Both methods took about the same amount of time, although I think I’m a little more thorough, so my “plot” has a few less than his…after 3 years of this.

The research seems to say that digging them out is the most effective method, as herbicides don’t touch them. The problem with this is, as you mentioned, the bulblets are small and the bulbs themselves can be so deep.

It’s true that if you cut the tops off every 1-2 weeks they will eventually starve, but you have to be very diligent and it’s hard to keep it up for a whole season. Since you have only a few clumps, I would still go with the digging method. I’m going to try that this year with a screen to sift out the smaller bulbs.

I had great success one year telling my grandchildren that they were buried treasure, inviting them to dig with gusto. But that only worked once. I’m on my own again. Persistence is the key for whichever method you try. Thank you so much for being willing to recognize a highly invasive plant and begin the process of getting rid of it.

Hang in there – after four years I’m down to plants I can manage. – Rhonda Frick-Wright, OSU Extension Master Gardener

This rhododendron may need a shader spot.OSU Extension Service

Q: I have three rhododendrons and one is fairly healthy but it has yellow on the leaves and the other two are very sparse. How can I bring the sparse plants back to life and how can I get rid of the yellow issue on the leaves of the healthy one. – Washington County

A: All are seriously stressed, including the leafiest one. (I don’t really know why that one appears to be in much better condition than the others. Perhaps it has a larger root system.) In any event, it will take an extended effort to help the rhodies return to a healthy state, an effort that should focus on regularly scheduled supplemental irrigation, especially during the dry months.

Frankly said, the only way to get rid of both the brown spots and/or the yellow tissues, is to grow new, healthy leaves. The most obvious results of long-term stress are:

  1. Dark brown spots are sunburn, most likely acquired during last year’s excessive temperatures
  2. Yellowing of leaves is where chlorophyll has literally been bleached and killed
  3. The missing leaves and bare, scraggly branches are due to a stressed, low-energy shrub too weak to retain older growth

Much of the stress can be attributed to an inadequate water supply, combined with what appears to be a full-sun exposure. The single drip hose should be supplemented by at least two more drip lines placed concentrically within the outer ring, each one closer to the shrub. Then the system should be run long enough to thoroughly moisten the soil to 12-15 inches deep, once every three weeks through the dry months. The necessary run time to accomplish that may require one to 1.5 hours. (To determine if the soil is adequately moist after an irrigation, probe the soil with a trowel.)

Then, to help conserve soil moisture, whether naturally occurring or supplemental, add a 3-inch-deep mulch of bark chips throughout the rhododendron planting. A particularly helpful side effect of the organic mulch is that it will slowly degrade, thereby providing an extended supply of fertilizer elements for the shrubs.

Another option is to replace the rhodies with shrubs that are better adapted to a sunny site, and potentially to a more water-thrifty diet. You might consider visiting several local garden centers to see, and ask about, various spring-flowering shrubs that will be a better fit to your site. Jean Natter, OSU Extension Master Gardener diagnostician

Ask an expert

Why is this tomato start turning purple?OSU Extension Service

Q: I am wondering if you could help me identify what is going on with my heirloom tomato starts? They are under good-quality grow lights in our house. Germination seemed normal and everything seemed to be going well, until it wasn’t. The symptoms started with the ‘Vernazza’ variety cotyledons turning purple. Next the purple color spread to the first true leaves right above the cotyledons and little bumps appeared on the underside of the purple leaves. As the leaves were getting ready to fall off, they formed a noticeable thick whiteish band around the stems. It almost looked calcified, but wasn’t hard in texture.

The leaves started to curl and at this point we realized it was all of the ‘Vernazza’ variety. It then started spreading to the other tomato varieties, so we isolated all the tomatoes away from the other solanaceous crops. I looked at the roots, and I don’t see anything unusual, I also don’t see any pests.

I was wondering if you have seen this issue before? I plan on reseeding but I am tempted to not seed any ‘Vernazza’ with fear that the seed is what is infected? I reached out to the seed company to also see if they had heard or seen this happen. – Multnomah County

A: First the good news, it is not an infectious disease problem but rather a physiological response by the plants associated with low light conditions and high humidity. Low transpiration rates along with a rise in water absorption due to wet soils increase cell pressure, causing the eruption of epidermal cells so that inner cells enlarge and protrude. Leaves can also exhibit curling and distortions; Sometimes the affected leaves may drop from the plant. Oedema will not spread from one plant to another, but certain varieties are genetically predisposed to develop symptoms earlier or to a greater degree compared to other lines when multiple varieties are sown alongside each other.

You can decrease this problem by providing brighter lighting and/or decreasing the watering amounts or schedule, especially during rainy or overcast conditions. The purplish coloration is a common expression by tomato, but sometimes greater appearance of it can signify that the plants are under stress. Overly wet soil conditions can lead to the stems, petioles and leaves expressing more of this purplish pigmentation. Otherwise, it can be a sign of a nutrient deficiency such as a phosphorous deficiency. But since your seedlings have oedema, I think that the coloration is due to the wet soil, too.

Good luck. I hope that you have a bountiful tomato harvest this season. Cynthia Ocamp, OSU Extension plant pathologist

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