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

The gardening season has started and you may have some questions. For answers, check out Ask an Expert, an online question-and-answer tool from Oregon State University’s Extension Service. OSU Extension Teachers and Master Gardeners respond to questions within two business days, usually less. To ask a question, simply go to OSU Extension Website, enter it and include the county where you live. Here are some questions asked by other gardeners. What is your?

Q: I have a few clumps of bluebells infesting different parts of my garden and have read that they are invasive and quite difficult to get rid of.

Some people say digging up the bulbs, but it’s difficult because there are many baby bulbs escaping. Another tip says to tear off the leaves/flowers to starve the bulb. I even read advice that said to trample the leaves. Do you have any suggestions on how to get rid of these plants? – Multnomah County

A: I am also in your place. I have a large patch of bluebells.

One year I even bet my husband that his method of burning them wouldn’t 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 bit more thorough, so my ‘plot’ has a bit less to it than his…after 3 years of this.

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

It is true that if you cut the tops every 1-2 weeks they will eventually starve to death, but you have to be very diligent and it is difficult to maintain this for an entire season. Since you only have a few clumps, I would always go for the digging method. I’m going to try that this year with a screen to filter small blisters.

I had great success one year telling my grandchildren they were buried treasure, inviting them to dig with enthusiasm. But it only worked once. I am alone again. Perseverance is the key to whatever method you try. Thank you so much for agreeing to recognize a very invasive plant and beginning the process to get rid of it.

Hang in there – after four years I only have factories I can handle. – Rhonda Frick-Wright, OSU Expansion Master Gardener

This rhododendron may need a more shady spot.OSU Extension Service

Q: I have three rhododendrons and one is quite healthy but it has yellow on the leaves and the other two are very sparse. How can I revive the sparse plants and how can I get rid of the yellow problem on the leaves of the healthy plant. – Washington County

A: All are seriously stressed, including the leafiest. (I’m not sure why this one seems to be in much better shape than the others. Perhaps it has a bigger root system.) Either way, it will take a prolonged effort to help the rhodies to regaining a healthy state, an effort that should focus on regularly scheduled supplemental irrigation, especially during the dry months.

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

  1. The dark brown spots are sunburn, most likely acquired during the excessive temperatures of last year
  2. Leaf yellowing is where the chlorophyll has literally been bleached and killed
  3. Missing leaves and bare, unkempt branches are due to a stressed, low-energy shrub that is too weak to maintain older growth

Much of the stress can be attributed to an inadequate water supply, combined with what appears to be full sun exposure. The single drip line should be supplemented by at least two other drip lines placed concentrically in the outer ring, each closer to the shrub. Then the system should run long enough to thoroughly moisten the soil to a depth of 12 to 15 inches, once every three weeks during the dry months. The runtime required to accomplish this may require one to 1.5 hours. (To determine if the soil is sufficiently moist after an irrigation, probe the soil with a trowel.)

Then, to help retain soil moisture, whether natural or supplemental, add a 3-inch-deep mulch bark chips throughout the planting of rhododendrons. A particularly useful side effect of organic mulch is that it breaks down slowly, providing a prolonged supply of nutrients for shrubs.

Another option is to replace the rhododendrons with shrubs better suited to a sunny site, and possibly a more water-efficient supply. You might consider visiting several local garden centers to view and ask about various spring flowering shrubs that will best suit your site. – Jean Natter, OSU Extension Master Gardener diagnostician

Ask an expert

Why is this tomato starting to turn purple?OSU Extension Service

Q: I wonder if you could help me identify what is going on with my heirloom tomato debut? They are under good quality grow lights in our house. Germination seemed normal and everything seemed to be going well, until it wasn’t. Symptoms started with the cotyledons of the ‘Vernazza’ variety turning purple. Then the purple color spread to the first true leaves just above the cotyledons and small bumps appeared on the underside of the purple leaves. As the leaves prepared to drop, they formed a thick, visible whitish band around the stems. It looked almost calcified, but its texture was not hard.

The leaves started to curl and at this point we realized it was the ‘Vernazza’ variety. It then started to spread to other tomato varieties, so we isolated all tomatoes from other nightshade crops. I looked at the roots, and I don’t see anything unusual, nor do I see any pests.

I was wondering if you had seen this problem before? I plan to reseed but am tempted not to sow ‘Vernazza’ for fear that it is the seed that gets infected? I contacted the seed company to also see if they had heard or seen this happening. – Multnomah County

A: First of all the good news, this is not an infectious disease problem but rather a physiological plant response associated with low light conditions and high humidity. Low transpiration rates along with increased water uptake due to moist soils increase cellular pressure, causing epidermal cells to erupt so that inner cells enlarge and protrude. Sheets may also exhibit ripples and distortions; sometimes the affected leaves may drop from the plant. Edema does not spread from plant to plant, but some varieties are genetically predisposed to develop symptoms earlier or to a greater degree than other lines when multiple varieties are sown side by side.

You can reduce this problem by providing brighter lighting and/or decreasing watering amounts or timing, especially on rainy or overcast days. Purplish coloring is a common expression in tomatoes, but sometimes a greater appearance of it can mean plants are under stress. Too wet soil conditions can cause stems, petioles and leaves to express more of this purplish pigmentation. If not, it may be a sign of a nutrient deficiency like phosphorus deficiency. But since your seedlings have edema, I think the staining is also due to the wet soil.

Good luck. I hope you will have a good crop of tomatoes this season. – Cynthia Ocamb, OSU Extension Plant Pathologist

Edward K. Thompson