pruning wisteria

I have a wisteria that has gone untamed for a few years, and I need to know when and how to go about pruning it back to a reasonable size. It grows up the fence to a pergola-like structure, but it’s gone way past that to begin attaching itself to surrounding trees.

Local pruning expert Cass Turnbull of Plant Amnesty has written about pruning wisteria. Here is a link to the article on Plant Amnesty’s website. The relevant passage (about renovating an out-of-control vine) is excerpted below:

RENOVATION. If it gets away from you or you have moved into a home that already has an enormous wisteria tangle, grabbing and strangling everything in sight, show no mercy. Lop, saw and chain saw whatever is necessary to get it back down. I suggest you cut several feet below where you want the regrown vine to be, since you will experience an upsurge of new shoots the following spring. As with all heading cuts, the new growth occurs directly beneath the cut and heads up from there. You will need some room to let it regrow over the next few years. New
growth will be vegetative (not flowering) and rampant for a few years. I wouldn’t be surprised if some major stems die back partially or totally, if you make cuts one inch or over. But I doubt that you will kill the plant. As some stems die back, cut off the dead bits. Others will supply the replacement shoots to be tamed in upcoming years.

Local gardener Ciscoe Morris also has information about maintaining wisteria vines. Excerpt:

“To prevent damage to your house and to encourage flowering, prune the tendrils to about 4 inches from the main structural vines when they grow beyond a foot long. This is a form of spur pruning. It encourages flower buds to form by concentrating all of the energy that would have been used to grow the long tendril into a 4-inch stub. While you are at it, you may as well construct a shed under the wisteria to store your ladder, because within only a few weeks, new tendrils will begin to grow and you’ll be climbing up to do it all again.

The Royal Horticultural Society also has information on pruning and training wisteria in an article entitled Pruning and Training Wisteria.

According to the American Horticultural Society’s Pruning & Training (edited by Christopher Brickell; DK Publishing, 1996), the times to prune are midwinter and again in summer, about 2 months after flowering. With
an established wisteria, the goal of regular pruning is “to control extension growth and to encourage the production of lateral flowering spurs. The current season’s shoots are cut back in two stages to within two or three buds of their base. These will bear the coming season’s flowers. Growth and flower buds are easily distinguished in late winter,
the former being narrow and pointed, the latter plump and blunt.”

cottonseed hulls as mulch

Can cotton hulls be used as mulch on asparagus?

Here is what Stu Campbell’s book, Mulch It! (Storey Books, 2001) says about cottonseed hulls as mulch:

“These hulls can be used most effectively around plants such as beans,
which are suited to wide-row planting. Apply a 1- to 2-inch layer. Or you
can wait until the plants have grown 3 or 4 inches high, then sift the
mulch down through the leaves… Cottonseed hulls have a fertilizer
value similar to, though not as rich as, cottonseed meal. Because they
are so light, the hulls blow around in the wind.

Campbell discusses mulching asparagus with a choice of hay, leaves,
straw, old manure, and compost for winter protection. You can leave these
mulches in the spring, and the tips will emerge through the mulch. If you
wish to extend your growing season, he recommends dividing your bed in 2
parts in spring. Mulch one half heavily with fine material like cocoa
hulls, leaf mold, or ground corncobs. Leave the other half unmulched
until shoots break through the mulched side. Then mulch the unmulched
side. The half which was mulched earlier will bear a few weeks later than
the other half.”

The National Sustainable Agriculture Information Service has a web page on organic growing of asparagus crops which mentions other types of mulch (such as winter rye as a dying mulch and perennial ryegrass and Dutch white clover as living mulches) for this crop, applied at different times.

It sounds to me as if the main drawback with cottonseed hulls is their light weight. Otherwise, they should be acceptable as a spring mulch.

overwintering banana trees

I have a bunch of banana trees in a greenhouse that are turning brown. Some are totally brown and others are turning brown at the ends of the leaves. The trees are about 10 feet tall. Any idea why they are turning brown and what can I do to fix them?

Are you growing Musa basjoo, Musa ensete, or another species of banana? Also, I wonder if your greenhouse is heated or not. Here is a link to comments on growing Musa basjoo outdoors in the Northwest on the University of British Columbia Botanical Garden Forums.

According to this site, leaves which have browned from the cold can simply be removed in the spring. Here is a link to another discussion of browned banana leaves, from Houzz’s Forum.

Since your plants are under cover, there are probably different issues to consider, such as the humidity and temperature level in the greenhouse, and the amount of water the trees receive. They need to be kept moist but not waterlogged. Here is a link to general cultural information from California Rare Fruit Growers.

According to the book Exotic Gardening in Cool Climates by Myles Challis (Fourth Estate, 1994), Musa ensete [now referred to as Ensete ventricosum] is best overwintered in a greenhouse. It needs a large amount of water during the growing season to match the evaporation from its huge leaves, and it is a heavy feeder. Musa basjoo is the more ‘hardy’ banana. Here is what the Royal Horticultural Society (now archived) says about overwintering Musa ensete, or Ensete:

“To overwinter Ensete, our glasshouse is kept at 16C (61F) by day and 12C (53F) at night – at lower temperatures, lifted plants are prone to rotting. The lower the overwintering temperature, the earlier Ensete should be lifted and established in their winter containers, and the drier they should be kept subsequently. If only frost-free winter quarters are available, permanent container culture may be wiser. Musa species and cultivars are more forgiving of this operation, and can even be stored in a shed or garage.”

If you do not think that cultural conditions are the cause of the problem, you might look at this description of a disease affecting bananas.

Purdue University’s New Crop page has some information about diseases of banana.

You might also bring sample leaves to a Master Gardener Clinic if you suspect a disease is causing the leaf problems. For information about Clinic hours see their website (Plant Clinic Schedule).

diseases that affect Cyclamens

I am a collector of Cyclamens and grow most of my collection in pots. I believe my C. purpurascens are infected with Botrytis, though I have not had this confirmed by any tests. Last year was particularly bad and I had to remove nearly every leaf from both my plants. This summer, as the new leaves emerged, I sprayed the leaves and surface of the grit with a sulfur solution, which seemed to dramatically reduce the infection rate. Now, the infection seems to be back. Can you suggest some methods of control? Do I have to have it confirmed first? I repotted them early this summer, and sterilized the pots and replaced the grit at that time. What else can I do?

What you have done to control Botrytis is what is recommended by the Pacific Northwest Plant Disease Management Handbook. It does indicate the Botrytis can be seed-borne and grow systemically in the plant. Your real solution may be to obtain plants that are certified disease free.

However in researching Botrytis online, I found an article, “Botrytis Blight of Flowering Potted Plants” in Plant Health Progress, from Plant Management Network International. This article was written by a researcher at Cornell University who suggested that Cyclamen are also susceptible to Fusarium wilt and that the symptoms are quite similar. Therefore, I do think it would be wise to take a sample of your diseased plants to a Master Gardener clinic for confirmation. The Master Gardener clinics in Thurston County can be found at their website.

growing bamboo in containers

I am new to the area, and am renting a house that has 3 containers of bamboo plants on the deck. Two of them appear to be dead or dying, although there is still green in the canes. I tried watering them a lot for a week or so, and for one day they seemed to like that, but then they did not any more, and looked worse. Some theories people have offered: the soil is depleted, they need to be thinned, they have been poisoned somehow. Any advice? Or should I just get new ones? And, where would I get new ones?

Bamboo can grow well in containers, but it can also be picky about drainage, fertilizer and container depth.

Here is an American Bamboo Society article (now archived) entitled Planting and Caring for Bamboo.

Your bamboo may have a pest or an infestation of some kind. To be sure, you may want to bag a sample of the leaves and take them to a Cooperative Extension Master Gardener Plant Clinic. Master Gardeners are trained in the identification of plants and pests and a host of other botanical subjects.

To find out where to purchase bamboo locally, try Bamboo Web’s sources search tool.

diseases that affect rhododendrons

My rhododendrons have a problem. What appears to be a white powder covers the buds and spreads up the leaves. What is it, and what can I do to stop it?

I cannot be absolutely certain without seeing the plants, but it sounds as if your rhododendrons could have powdery mildew.

Here is an article from the Washington State University Cooperative Extension which describes this disease. One preventive measure you should certainly take is to clean up all the fallen leaves and twigs under your rhododendrons, because the fungus which causes powdery mildew can overwinter there.

You could bring in a sample to a Master Gardener Clinic, and ask if they can diagnose the disease as well (they are at the Center for Urban Horticulture and other locations–see their website.

dividing Phormium

Can I divide New Zealand flax without killing it? When should I do it? My adult plant, about three years old, has two very healthy looking youngsters that I would like to move.

The best time to divide Phormium is spring, according to American Horticultural Society’s Plant Propagation (DK Publishing, 1999), but what you are describing are new offsets, so you will not be splitting the entire crown of the plant, but instead separating them from the parent plant. Wear gloves when working with Phormium. You may be able to use two garden forks to separate the youngsters from the parent.

bark peeling away

The bark on a Coral Bark Maple is peeling away on one side of the trunk…about 1 1/2 to 2 feet long. The tree looks healthy otherwise. Cause? Anything to do?

Trees (maples and others) are attacked by various diseases and pests, but nothing that removes sections of bark on a trunk. Damage might be from larger pests such as raccoons, deer or squirrels. In the city, squirrels often strip bark from trees for their nests. You might want to:

1. Put chicken wire or other protective barrier around the tree. The tree will heal itself as long as the entire trunk is not girdled (that is when bark is stripped all the way around the trunk so moisture and nutrients can’t flow).

2. Have an arborist look at the tree for an accurate diagnosis. To locate an arborist in your area, contact Plant Amnesty’s referral service or call their Referral Service Coordinator at 206-783-9813 and leave the following information:

Name

General Location (city or town)

Phone Numbers (work, home, cell)

Email (will get the quickest response!)

transplanting lilac

I have a dark purple lilac tree growing on the north side of my home. It does not get a lot of sunlight. I am wondering about replanting it somewhere else in the yard. When can I do this?

Lilacs should be able to tolerate moderate shade, according to The Plant Care Manual by Stefan Buczacki (Crown Publishers, 1993). You can move it to a sunnier location to see if it will thrive there.

The best time to transplant a lilac is before it leafs out (late winter, when it is dormant) but apparently they are somewhat tolerant of being moved at less-than-ideal times. The University of British Columbia Botanical Garden discussion forum also recommends transplanting lilacs in dormancy. Blooming should not be affected, unless your bush is already leafed out and in bud.

plants for a green roof

I am trying to select plants for a green roof on Lopez Island. I would like to use some native plants, and not have to do too much weeding. Can you help me?

The Miller Library has a booklist on green roofs which includes weblinks. With respect to weeds, as a former professional gardener I don’t believe there is a “maintenance-free” garden. However you may be able to come up with a freely seeding grass (Festuca ovina var. glauca comes to mind) that would do well and look good with other plants.

Regarding Pacific Northwest native plants (i.e., grasses), I recommend using a native plant book (such as Pojar and MacKinnon’s Plants of the Pacific Northwest Coast) and searching for those which suit the conditions of the site. You may also find King County’s native plant
guide useful, as it is searchable by site requirements. Washington Native Plant Society offers a similar plant selection guide. There are also native species of Sedum.

The book Green Roof–a Case Study by Christian Werthmann (Princeton Architectural Press, 2007) evaluates green roof plants and planting techniques, and includes observations regarding soil depth, the factors affecting desiccation (i.e., metal edging and the planting medium/size of the plants used), and density considerations. Here are some of the conclusions of the case study:

p.69-insects and other invertebrates need >6″ of soil to survive the cold;
drought tolerance increases with soil depth; probability of seed germination also increases with soil depth
p.76-erosion control (bird repellant?) made from a degradable straw mat (such a mat may be useful for preventing birds from pulling up the plugs)
Plants:
p.95-sweet fern Comptonia peregrine-not too vigorous, suffered from weed infestations
p.96-prickly pear Opuntia fragilis-did well
Phlox subulata, Silene caroliniana-did well
Sedum telephioides, S. lanceolatum, S. stenopetalum-suffered from heat, drought, and birds-these were replaced with European sedums (S. album, S. reflexum, S. spurium, S. cauticola, S. sexangulare, S. floriferum, Sempervivum tectorum, Orostachys boehmeri) and not planted as plugs but as larger plants that started in the green roof substrate (reducing transplant shock)
p.100-mixed prairie perennials with sedums (in 6″ soil), which filled in when perennials died-the architects note that there is no record of prairie plants doing well on green roofs, therefore the backup with succulents-they also note that metal roof edges speed up desiccationPerennials included ice plant (Delosperma nubigenum; my note: be careful about this, as it’s a noxious weed in California and if it spreads by seed, it might become a problem on Lopez); flameflower (Talinum calycinum); Eragrostis spectabilis; Allium schoenoprasum; Allium cernuum; Bouteloua gracilis; Elymus virginicus; Achillea millefolium; Tradescantia bracteata; Solidago nemoralis; Artemisia ludoviciana; Coreopsis verticillata; Asclepias tuberosa; Rudbeckia hirta

p.105-in 3″ soil with nearby metal (and thus an overheating issue), they used proven sedum species; heat from metal can be reduced by using aluminum (proved cooler than wood)

p. 108-conclusions: use a combination of indigenous plants with “successful green roof performers”-thin soil and high light “even overtaxed the hardiest succulents”-soil depth and temperature extremes made a big difference; even a slight difference in soil depth in a harsh environment can mean the difference between success and failure-continuous care and maintenance in the beginning is important for success-plugs grown in peat moss were less successful, since completely dried-out peat moss repels water-dense plantings (and/or rapidly spreading plants) important because bare soil gets hotter than soil covered by a plant.