Now that you’ve spring-pruned your rose bushes and climbers, it’s time to assess their health. If they’ve started leafing out already, that’s good news. If some canes are black, scratch a cane with a fingernail. If it’s dry and black or brown wood under the outer coat of the cane, that cane is dead. If you can cut out the blackened part of the cane down to a green part, remove the black part.
If your scratch into the cambium is red to chocolate brown, and moist and oozing, it has bacterial cane blight. This rose disease, related to Pseudomonas syringae, appeared in the Treasure Valley a number of years ago and is now known as bacterial cane blight. It may show up in the spring or summer, entering through a pruning wound or where a leaf has been torn from the cane. Try to prune at least 10 inches below the visible disease, then soak your pruners in bleach solution, and spray that shrub with a copper-based fungicide such as Phyton 27. Bleach solution is one part bleach to 10 parts water. Plant physiologist Dr. Krishna Mohan also advised spraying a surviving shrub with Phyton 27 in the fall, when half of rose leaves fall, and a third time in spring.
In our area humidity is usually very low, and unless we have an unusually rainy spring, we don’t have problems with black spot on rose leaves. Black spot and many other diseases are fungi, and may be prevented by generous mulching around plants (not up against the stem or canes of plants) to prevent fungal spores splashing from soil to leaves or stems. This holds true in ornamental and vegetable gardens, especially preventing blights on susceptible plants such as tomatoes.
Many fungal disease spores are ubiquitous on soil, but if we can prevent their transfer to foliage, we can prevent infection of desirable plants.
Perennial plant of the year
Most of us love to watch celebratory fireworks, small explosions in the sky that briefly leave tracers in a ball formation, but what if you could have that patterned sight that lasted for days or even weeks? You can, but you don’t look skyward, look toward the ground.
We know that onions, scallions, chives, garlic, leeks and shallots belong to the genus allium, but there are also many ornamental varieties of allium available, all blossoming in variations of the ball or spherical shape, with tiny flowers (and later seeds or bulbils) at the end of each filament. The genus contains more than 700 species, some perennial, others biennials (that we grow as annuals). One of my favorite blossoms is that of the allium Schubertii, with tiny blossoms at the ends of short and long filaments.
This year the perennial plant of the year is allium Millenial, which grows 12 to 18 inches in height, sports lavender blossoms in July and August, and is hardy to USDA zone 5. It’s said to be deer-proof, too, as are many alliums. Alliums grow from bulbs, sets, seeds and seedlings. The Idaho Department of Agriculture has ruled that “No person shall import into the designated counties bulbs, sets or seedlings of onion, garlic, leek, chives, shallots or other Allium species, including ornamentals, for planting purposes [unless they were produced in] Ada, Bingham, Blaine, Boise, Bonneville, Canyon, Cassia, Elmore, Gem, Gooding, Jefferson, Jerome, Lincoln, Madison, Minidoka, Owyhee, Payette, Power, Twin Falls, and Washington Counties, state of Idaho. and Malheur county, Oregon.”
Note that seeds are not included in this quarantine.
This quarantine is intended to protect the onion-growing producers from a disease called white rot whose sclerotia could be carried by surface water to irrigation water, infecting fields to the southwest. Once white rot is found in a field, it cannot be eradicated or cured with our current knowledge and materials, and that crop may not be grown again in that field. The southwestern Idaho and eastern Oregon onion growers produce more onion poundage annually than any state in the union. Unfortunately, ornamental onions are subject to the same diseases as edible ones, and so are included in the quarantine.
Many varieties of allium are produced in the approved counties, and bulbs, sets and seedlings for them may be bought at locally-owned nurseries and garden centers. I usually sow shallot, leek and onion seeds indoors in early spring, then transplant into the garden, usually interplanting with other garden plants. Allium seeds are usually only viable for one year unless they’ve been pelletized. Pelleted onion seeds may be viable for five or six years.
Send garden questions to firstname.lastname@example.org or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.