The gardening season is rolling and if you’ve got questions, 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: A landscaper put a single cattail as a decorative touch by a dry creek he’d created in a flower bed. The first year it looked exotic. The second year, I was excited it returned. The third year (now) I spent a great deal of time this winter deep-digging each cattail to remove as much tuber as I could. Then I replanted the bed with perennials.

Ugh! New cattail spikes have returned. What shall I do? I turned that flower bed upside down last winter with a massive mound of tubers and now I’m looking at a dozen new spikes.

Have people had success with the homemade vinegar/salt weed killer? What about touching the base of the new cattail spike with a squirt of Roundup? I’ve never used a “heinous” product like Roundup but, there could come a time. – Josephine County

A: Keep digging those tubers! I don’t mean to be flippant about your problem. Cattails (Typha latifolia) may be exotic looking, but that brown head is full of literally thousands of tiny fruits. When they erupt at the end of the season and fly away on the wind or drop into your “dry pond” they often hit pay dirt. The maintenance staff at Lithia Park in Ashland has done extensive trials of vinegar-based weed killers. The results have all been disappointing. With a tough plant like cattails, I cannot recommend this treatment.

Using glysophate need not be “heinous.” I don’t know how many cattails you need to treat. Cut them off at about 4 inches above the soil and paint the glysophate (Roundup, etc.) on the cut edge. This limits its contact to the plant you want to kill. You may have to repeat this treatment, but it has proved successful with noxious weeds such as Japanese knotweed, which is a very tough, almost bamboo-like weed. I’m thinking that your digging was probably more successful than you feel; it is the seeds and the ability of even a small piece of rhizome to promote continued growth that proliferate the plants. You may actually be winning part of the battle already. – Marjorie Neal, OSU Extension Master Gardener

With some work, clay-based soils can be a good plant medium

Q: Just bought a new old house (1996). While the house does have rhododendrons and other shrubs, I have found the existing soil very hard and lifeless when I have tried to enhance the ground before planting perennials like lavender, etc. I am going to take out some of the existing horribly pruned shrubbery and fill some of the blanks. How is the best way to improve and break up the existing rock-hard dirt? Using a shovel or pick is not an attractive option. – Washington County

A: Judging from your statement that the ground is very hard, it’s likely that you have a clay-based soil. In spite of the many complaints you may have heard, or read, about clay, it’s an excellent media to grow healthy, vigorous plants.

Problems develop with clay in the following conditions:

• When it’s dry, it’s as hard as concrete
• When it’s soggy, it’s mucky and clings to your shoes
• When it’s dry, it’s challenging to moisten without losing water to runoff (either apply water using sprinklers with successive on/off cycles, or wait until the fall rains begin)

Among clay’s benefits are these:

• Holds fertilizer elements well
• Holds moisture well
• Contains a number of naturally-existing fertilizer elements, among them potassium and magnesium
• Provides a sturdy growth media that supports plants

Before you even start removing and/or installing plants, consider waiting until fall to see what you may want to preserve as well as what changes are necessary to achieve your vision for the property. Fall and winter is a good time to plant, plus you’ll have the benefit of rainfall to moisten the ground well.

Consider the following:

• Until you’re ready to start the garden renovation/renewal, use soaker hoses to irrigate existing planting beds of flowers or vegetables, and/or to wind through a hedge. Connect the hoses to an outdoor spigot; add a mechanical timer to set runtime; and use only enough pressure that the hose sweats. (The low flow required for a soaker hose works well with timers you can set for minutes/hours, but not those rated in gallons.)
• Run the irrigation system long enough that soil is moistened to 8 inches deep for existing herbaceous (green) plants, 12 inches for woodies; to test, probe with a trowel.
• Use an organic mulch such as wood chips to conserve moisture for existing shrubs and trees. After the renovation, also use mulch for the new plantings.
• Delay planting until fall but, during the intervening time, decide what you will do including drawing up a planting plan and locating sources for the desired plants and supplies.

After the soil is appropriately moist to dig and amend – see below – rent such tools as a mini-front-end loader or a mini-garden-tractor to help with the heavy-duty tasks of soil preparation, including moving and incorporating soil amendments. See How to Use Compost in Gardens and Landscapes.

A simple test to determine appropriate moisture content to work the soil is as follows:

• A clay soil is too dry if you can’t easily grasp a handful
• A clay soil is too wet if a handful, when squeezed, dribbles
• A clay soil is at the correct moisture content to dig, amend, or till when a squeezed handful holds together after it is released.

– Jean Natter, OSU Extension Master Gardener Diagnostician

What’s on this azalea bush?

Q: What are these white egglike spots on my bush? – Clackamas County

A: That’s a humongous population of azalea bark scale (Eriococcus azalea)! Azalea bark scale are small sucking insects that can cause their most common victims – azalea, pieris and rhododendron – to slowly decline over an extended period of time. (Certain other shrubs may also be affected, but far less often.)

You can physically attack those small beasts by rubbing them off with a toothbrush. Then, because you’re very likely to miss the small, newly hatched larvae (youngsters), follow up with a commercial insecticidal soap spray, diluted according to label directions. Coat all surfaces of the stems and branches thoroughly, front and back, top and bottom. Then repeat the spray, as needed, through the following months. – Jean Natter, OSU Extension Master Gardener Diagnostician

Do windmill palm flowers need to be removed?

Q: My windmill palm is flowering with about eight clusters. Should they be cut off? Is it better to remove or leave them? It is outside and about 5 years old, and this is its first time flowering. I don’t mind the flowers but if it is putting too much energy into the flowers I would rather it put the energy into growth. Would it help to cut them now and in the next season’s growth? – Linn County

A: A windmill palm is pretty hearty around here and while it may have a few issues with aphids or sometimes a fungal disease, there is nothing wrong with leaving the flowers on the tree.

I am attaching a link to information about the windmill palm from Oregon State for your review. Since you are more interested in the growth of the tree, you can take off the flowers. That should give the energy to the growth of the tree.

Mix natural soil with new amendments to get the best results

Q: We just built raised beds that are 2 feet deep. We are thinking of two types of soil; one is 1/3 sandy loam, 1/3 mushroom compost, 1/3 premium compost, the other is 55% fine dark fir, 30% garden mulch, and 5% each of pumice, sand, and mushroom compost. Which of these two mixes would you suggest? Or, do you have other suggestions? – Multnomah County

A: Your first suggestion sounds closer to the recommendation listed here. Note the importance of mixing some of the natural soil beneath the bed with whatever you choose so there is not a water barrier created by two completely different soil types next to each other.

In addition, here are recommendations from Oregon State Extension and some good tips for raised bed gardening. They don’t get as specific about soil but again, notice the recommendation to mix some of your natural soil in with the soil you are ordering. There is also some really good information about raised beds in general in this article. – Rhonda Frick-Wright, OSU Extension Master Gardener