Horticulture Guy

Q. I have a section of a planting bed two 1/2 wide running north & south along the west side of a fence. It gets plenty of afternoon sun. The problem is that the Irises, which used to bloom there haven’t bloomed in several years even after lifting & dividing. Also I tried some Peonys and I’m seeing root rot. With white rhizome looking lines. Is the soil not draining properly? How do I fix it? Ward Neils - Tacoma, WA

A. Thanks for letting me know about the root rot on your peonies since this indicates to me that the soil stays wet. This makes the Peonies prone to root rot. Although some Iris are suitable for wet sites not all are. The best varieties for wet sites are Japanese (Iris ensata) Yellow Flag Iris (Iris pseudoacorus) Siberian Iris (Iris sibirica), and Blue Flag Iris, (Iris versicolor). Other Iris do not do as well in wet soil conditions. Although crowding (solved by division) is one of the conditions sited when Iris fail to bloom regularly, there are other conditions that can also be causing this problem. One example is when an area receives less light over the years due to the growth of nearby trees or shrubs. Two other examples are planting the rhizomes too deep and over fertilization. Assess your situation and determine which may be the culprit and correct the condition or conditions if more than one applies. A solution for wet soil is to build raised beds along the fence. Pruning nearby trees and shrubs to allow additional light, testing your soil (with a SOIL TEST KIT )before fertilizing will ensure proper fertilization and a shallower replanting would address the planting depth issue.

-- HG

Q. I have a 30′ tree I think it is called a “tulip” tree because its flat green leaf shape resembles a flat open tulip. the tree also has a type of flower that resembles a fluted kings crown. It tapers up in a yellow brown and has a rim od yellow. It is quite beautiful. It has bloomed for the last 20 years or more. This year all the budded flowers are dry shaped ready to open but have not. In fact there is not one bloom that has opened. The tree looks great, no signs of any disease. We have it injected for insect control (read billions of aphids) for probably 10 years. Any help would be appreciated. Bob Miller – Lakewood, WA

A. Yes it sounds like you have the Tulip Tree (Liriodendron tulipifera) which some people see a tulip in the leaf shape and others in the flower itself. Aphids as well as scale (brown round stationary insects along the stem) are both insect pests. But if you are controlling the aphids with the “injected” pesticide you should also control the scale. Horticultural oil sprays are also effective in controlling these pests. Tulip Trees are also susceptible to verticillium wilt (a soil borne fungus) powdery mildew, leafspot and cankers. None of these would directly influence the trees flowering. The condition you describe sounds like bud blast, which prevent the flower buds from opening. Insects, fungal disease or poor growing conditions can cause bud blast. Bud blast occurs on many ornamental plants including true tulips and rhododendrons. Since it takes at least 10 years for the Tulip Tree to flower and you say it has bloomed for 20 you probably have a large tree. Since you know you have aphid problems it is possible that although you are trying to control the aphids systemically it has not been entirely successful. The aphid feeding could be causing the bud blast. The height of the tree makes it hard to verify. You may want to consider hiring a professional that has the proper equipment to assess insect populations and to spray horticultural oil on large trees. If the tree is small enough you can use Ready-to-Spray Horticultural Oil which attaches to your hose end using water pressure.

-- HG

Q. Dear Peter! Thank you for your column in the Tribune. My problem is this: I have several Oxalis plants; I think they are Oxalis purpurea. They provide beautiful mounds of green with their rose pink blossoms. Around right now though some of the mounds’ leaves turn brown and curly. What causes this? Our garden tends to be moist – on a hillside. Also how do you get rid of buttercup? Karen Morris - Tacoma, WA

A. Unless you have a warm microclimate in your garden is unlikely if that you have Oxalis purpurea since that a South African native and not generally hardy in the Puget Sound region. Oxalises are notably pest free regardless of which species you have. It is difficult to say exactly why some leaves are turning brown and curling. I could be something cultural. The only disease I know of related to Oxalis is a species of rust that also uses corn as a host. It does not sound like the problem is threatening to the plant so I would just remove and dispose of the effected leaves.

-- HG

Q. We have a very old, well-established wisteria covering almost the entire front of our house. Unfortunately, two of the three largest branches, which are approximately 12 feet in length, are being held up in part by a wooden fence/arbor which we need to remove and replace due to rot. Is there any way to drastically prune back these branches without losing the plant? Or, in the alternative, do you have any suggestions on how we could possibly prop the plant up without doing major damage until a new arbor is in place? Angela Krupa - Tacoma, WA

A. There is little doubt that if you cut the branches back you would get new regrowth below the cuts. You might get more than you hope for and will have to selectively prune to select a new leader that will go back over you new structure. But with a little ingenuity you may be able to prop them as you mention in your question. What may work in this case is a dry-wall T-Square. You can buy them at your local hardware store, but in your case you may want to build your own. You can then make them the appropriate lenght to support your wisteria vines. You can make a “T” one from 2×4’s and making the letter “T” by taking a short piece and nailing it to a longer piece. Use more than one nail so the smaller piece doesn’t swivel around on the single nail. There are many modifications you can make to this basic design to suit your needs. Then you slide the “T” under the vines. You may need a few to be successful. This will take the weight off the decrepit structure and allow you to replace it. Then release the “T” and ease the vines onto your new structure.

-- HG

Q. Hi Peter: I was recently at the Seymour Botanical garden in Tacoma, WA and saw a Valentine Hoya. It had heart shape leaves and a black blossom… very unusual, but I have to have one. Would you know where I might find one? I would appreciate an email response. Thank you, Shirley Owens - Olympia, WA

A. I contacted the Conservatory and with help from Susan Hulbert
Communications Manager and Mary Anderson and found that they don’t sell the Valentine or Sweetheart Hoya (Hoya kerri) at the conservatory but they are available online at plantsforkids.com. Mary also mentioned that Hoya publicalyx is entwined with the Valentine Hoya and it has a deep red (almost black) flower. So you may have been enamored with this Hoya and understandably mistook it for the Valentine Hoya, which has creamy pink flowers with a dark chocolate brown center. Many Hoya flowers are fragrant as well making them extra special in my book. Mary is looking into local sources. If any one reading knows of any local sources you can contact me and I will pass on the info and post it on my website. If readers would like to see what all the excitement is about they can visit the conservatory, which is located at 316 South G Street in Tacoma’s Wright Park. Operating hours are Tuesday through Sunday from
10 a.m. to 4:30 p.m. The Conservatory is closed on Mondays.

-- HG

Q. As the apple maggot larvae live in the ground, is there an effective treatment to apply before they hatch? Is it time to start spraying my apple trees for the apple maggot?

A. This is a timely question since today’s Insect Alert is for the Apple Maggot. The larvae have been in the dormant pupae stage over the winter and are in the process of emerging from the ground as adult flies as you read this column. The first line of defense is laying out tarps under the trees in the fall to prevent infected apples from reaching the ground and releasing the larvae. The next step is larvae control. A specific species (Steinernema feltiae ) of beneficial nematode has been found effective for control of larvae in the soil. These beneficial nematodes are available online and sometimes can be ordered through garden centers. To determine presence of the adult flies (for the purpose of spraying) use either the sticky red apple traps or the yellow sticky traps. There is an organic spray made from kaolin clay (used in the food industry for its anti caking effect) and sometimes goes by the trade name Surround WP Crop Protectant. You can also monitor and manage the adults flies using the Apple maggot traps and lures None of these controls are perfectly effective so I always suggest protecting some of the fruit with plastic bags. Tie them around the fruit to prevent the flies entry. Be sure to leave enough room for developing fruit. This is an insurance policy for some larvae free eggs.

-- HG

Q. Have lost several young cherry trees. Problem seems to be boreres that stress the trees - evidence of sap seeping out of possible entry wounds. Can a systemis insecticide be used? If not, what? John Delaney – Puyallup, WA

A. I have Peach Tree Borers on my cherries this year as well. The sap you see oozing is the trees defense mechanism. When the trees are healthy and well watered the oozing of sap often flushes out the borers. You can also help by taking a thin but strong wire and inserting it into the hole through the sap “skewering” the borer. Systemic insecticides are not recommended on cherries used for consumption since the insecticide will be present in the fruit. Moths lay eggs on the trees and their larvae are the borers. Commercial growers use pheromone traps to catch the adult moths and time their sprays once the eggs are laid. Once the larvae (borers) hatch from the eggs they can be sprayed. But once they bore into the tree external sprays cannot control them. This makes timing critical. Skewering is the best control for the home gardener. Bud break is the time to start looking for the borers.

-- HG

Q. Do insect sprays lose their effectiveness by being carried over from the previous year? Bill McMonagle – Tacoma, WA

A. Yes. Although manufacturers are not required to put an expiration date chemicals can slowly loose their effectiveness over time. In most cases you can expect to get 1-3 year shelf life from the average spray. In other cases they may be effective for over 5 years. But there is no sure way to gauge this gradual loss of effectiveness. There are many variables that come into play. For example insect sprays that depend on living organisms like Bt (Bacillus thuringiensis) can loose their effectiveness faster than other types of sprays depending. But this also depends on the formulation of the Bt. The liquid formulation has a shorter shelf life than the powder formulation when stored under the same conditions. Also, once the seal has been broken and the contents have been exposed to air the spray will loose effectiveness more rapidly than if the product has not been opened. The temperature and storage conditions will are also critical factors. Extreme high or low temperature storage, exposure to sunlight, or high humidity will shorten the shelf life of sprays. The process is gradual. Although the product may not be fully effective it still may provide control of the insect. Since there is no way of knowing the loss of effectiveness I would not try to compensate by using more than the recommended amount or you run the risk of an over application which can be detrimental. Store sprays in a cool dry place that is out of the reach of children and pets. Areas that stay between 40 and 80 degrees are best. I suggest that you only purchase as much as you will use in a season or two. If you can’t use the smallest bottle of concentrate then consider using a ready-to-use (premixed in a hand sprayer) or ready-to-spray (premixed in a hose-end-sprayer) formulation.

-- HG

Q. Hello Peter, I have four grape vines, about eight feet long, that I planted a year ago. I want to have them fill in a grape arbor. Right now they are full of small leaves all along the vine. My question is, “What do I do to get the vines to spread out over the top of the arbor?” I seem to remember reading that cutting off these leaves is one way to do it, but I am concerned about harming the vines. Vincent Troccoli – Edgewood,WA

A. From your question I am assuming you are trying to increase the length of the vines so that they span the top of your arbor and want to limit side growth (laterals). The best way to do this is to pinch back lateral growth that is not contributing to the vines vertical growth up and over the arbor. But it is best to leave four or five leaves on the lateral and pinch just above them. This allows these leaves to contribute energy to the plant without the drain of having an active growing point at the end. Since the lateral growth has just started you may need to wait until the five leaves appear before pinching out the laterals growing point.

-- HG

Q . Where should pruning cuts be made above the node, below a node, or between the nodes on a plant. Ruth Derby - Paden City, WV

A. Pruning cuts below the nodes are too low, pruning cuts between cuts are too high and pruning cuts above the node are, to quote a famous fairly tale character “just right”. Your goal when making a pruning cut is to leave as little extra wood above the new growing point as possible. Pruning just above the new node (or growing point) leaves less non-growing stem that the plant has to defend against bacterial and fungal infections. The small nub above the new growing point can be sealed off. Often on shrubs and roses the pruning cut is made on a slight angle to allow water from rain and irrigation to run off of the cut surface. A horizontal cut can allow water to accumulate. As little as a drop can promote and favor bacterial and fugal infections. Also using a bypass pruner like the Fiskar PowerGear hand pruner, is better than anvil type pruner since the cuts on bypass pruners are much cleaner. Anvil pruners tend to crush stems and are better for cutting dead wood and branches down.

-- HG