reversion in variegated vinca

The variegated vinca growing in light shade in my garden has lost its white borders. Should I move it to a sunnier location?

The technical term for a loss of variegation is reversion. Variegation can be affected by light conditions as well as other factors, as this information from the Royal Horticultural Society suggests: “Variegation may vary during the year and is often less apparent in late summer. Where there is a permanent loss of colour inadequate light is often the cause. Waterlogging can also lead to loss of leaf colour. Reversion may also occur where more vigorous green shoots outgrow variegated shoots.”

Here is a link to some helpful information about variegated plants, from a now-defunct website which was called Enjoy Gardening:
“Understanding all the science behind variegation is quite complicated, so here is the nutshell version. For variegation to be stable, the variegation trait must be caused by a mutated cell or a group of cells that are fit
enough to grow and multiply, and those cells must originate in a region of the plant where they are involved in generating new variegated gene cells. For example, if the mutation originates in a section of a leaf or stem where normal tissue can outgrow the mutation, the variegation pattern will often be unstable and disappear. However, when there is an ‘island’ of mutated cells within a growing point or tip, the variegation has a greater chance of
being stable… Of course, to every set of rules there are always exceptions, which is why it’s quite common for completely stable varieties of plants to lose their patterns over time. And that’s exactly what happens with some
variegated Euonymus shrubs when the ‘normal’ buds produce leaves that have more chlorophyll than the variegated leaves have. Having more chlorophyll allows the normal leaves to grow faster and to out-compete the variegated foliage. In this case, the solution to preserving variegation is to get out the pruners and to lop off the emerging threat of normalcy.”

As suggested above, you can try cutting off the non-variegated (‘normal’) foliage and hope that the variegated foliage will return to dominance.

planting hydrangeas

I would like to plant hydrangeas along a south-facing shed. The site gets some morning sun and quite a lot of afternoon sun from over the roof of the house. This area currently has moss growing on it and has not been previously used for planting. Your reply will help me to decide whether to plant there or not.

I have amended the area where I have planted the hydrangeas with chicken manure and compost. I dug holes about 14 inches deep and and about 14 inches square. I also put a spade full

Most hydrangeas will do well in sun to part shade although full sun in a hot climate would be too much. You also want to bear in mind that hydrangeas, especially Hydrangea macrophylla, prefer adequate moisture. According to Michael Dirr’s Hydrangeas for American Gardens (Timber Press, 2004), an inch of water once or twice a week should be sufficient as long as the plant’s soil needs are met (consistently moist, well-drained, acidic soil which is rich in organic matter such as leaves, compost, well-aged manure). Some species of Hydrangea tolerate heat better than others, according to Dirr. Hydrangea macrophylla, H. serrata, and H. umbellata do not fare as well as H. paniculata. Some species, like H. quercifolia and H. aspera, prefer shadier spots. Dirr recommends using drip irrigation for plantings of Hydrangea, specifically using drip tubing, extender lines, and emitters attached to a garden hose, possibly with a timer.

The Michael Dirr book says that good soil preparation (not just of the planting hole) ahead of time is the best thing for hydrangeas. He does not subscribe to the rule sometimes put forth, that the hole must be 3 times as wide as the root ball. I also consulted Hydrangeas: A Gardener’s Guide by Toni Lawson-Hall and Brian Rothera (Timber Press, 1995) which says the hole should be 2 times the rootball’s width and depth. Be sure to check the state of your plants’ roots. You want to make sure they are not coiled in a spiral or restricted in any way. You may need to tease out or prune the roots a bit before planting.

Professor Linda Chalker-Scott discusses planting procedures in her book, The Informed Gardener (University of Washington Press, 2008), advising that the planting hole only needs to be the depth of the root system, but twice the width. She also recommends against amending the planting hole in any way. Backfill the hole with native soil, not a soil amendment. The idea is not to ‘spoil’ the plant by putting rich compost just in the hole, which will deter the roots from spreading out into the surrounding area. Here is more of her writing on this subject.

You have already amended the surrounding soil, so the addition of gravel to the hole is not necessary, and is possibly not a good idea, according to general planting information from University of Minnesota Extension. Here is an excerpt: “If soil drainage is inadequate, species that are tolerant of poorly drained soils may be planted, or soil drainage may be improved. This can be done in two ways. If a hard pan is present (a compacted, impermeable layer of soil) with an underlying layer of well-drained soil, a hole can be dug down to the permeable layer to provide drainage for the planting hole. If the soil is poorly drained and there is no well-drained layer below, a tile system can be laid. This, however, is expensive and requires the assistance of a professional for proper design. Simply adding gravel to the bottom of the planting hole will further decrease oxygen availability to the root system.”

of gravel at the bottom of the hole to improve drainage as I suspect that the base soil is mostly clayey.

growing conditions for Ribes sanguineum

I received a gift today, a shrub/plant named Ribes sanguineum ‘Inverness White,’ and different neighbors have different ideas of where to plant it.

I only have a little shade in my garden. Will it take full sun, or does it need partial shade? How tall and wide will it get?

In my experience, Ribes sanguineum does best in partly sunny (or partly shady) sites, and does not need much water once established. The plant you have is Ribes sanguineum var. glutinosum ‘Inverness White.’ This cultivated variety is described by California Flora Nursery as 6 feet tall and wide, but plant size will vary with garden conditions.

University of California Berkeley Botanical Garden’s spring 1999 newsletter features flowering currant selections, including the one you have:
“Ribes sanguineum var. glutinosum ‘Inverness White’ is a proven fast grower with wonderful white flower clusters. As the flowers fade they develop a rosy cast, giving a bicolored effect. The typical form of this variety has pale pink flowers. Roger Raiche found this one on Inverness Ridge in Marin County, and it has since made its way around the state to various gardens, both public and private. This plant was featured, with other new introductions, at a national meeting of the American Association of Botanical Gardens and Arboreta […]”

leaf drop in Dogwoods

I have a couple of dogwood trees, both are about 40 years old. In the front yard is a pink dogwood approx 25 ft tall and in the backyard a white one, approx 50 ft tall. Each year in the spring for the past few years the leaves have been browning and falling off the white one. Now the pink one is beginning to develop the same symptoms. Is there anything I can do?

There are several possible causes of leaf drop in Dogwoods. Below, please find referral information for the Master Gardeners and two websites that contain information about pests and diseases of Dogwoods and methods used to control them.

To know for sure what is causing leaf drop in your trees, you may wish to consider bringing a bagged sample of the leaves to the Master Gardeners Diagnostic Clinic here at the Center for Urban Horticulture or another of the many Clinic locations. You can locate a Master Gardener Clinic within King County on this website (Plant Clinic Schedule).

You mentioned that the leaves of your trees turn brown and then drop. These symptoms are commonly found when Dogwoods have been attacked by Anthracnose.
The Washington State University Cooperative Extension’s “Dogwood Anthracnose” page may be of use in helping you determine whether your trees have this disease.

Hopefully, this information will get you started. If you would like more information or have any other questions, please be sure and let us know.

I hope that your trees recover!

insect pests that affect bamboo

I have a “fence” of golden bamboo that is approximately 8 years old. It has a black coating on the leaves as well as small white flying insects that scatter when I move the branches. Any ideas as what has invaded my yard?

While we cannot diagnose plant problems remotely, what you describe sounds a bit like aphids or whitefly.

This page (now archived) from the American Bamboo Society website also has information on insect pests that affect bamboo. Here is an excerpt, about aphids:
“Aphids love bamboo! There are over 50 species of Asian aphids known to feed on Asian bamboos. A good example is Astegopteryx bambusifoliae, which sucks sap from the leaves of Bambusa, Phyllostachys, and Dendrocalamus throughout Southeast Asia. It over-winters on the bamboo plant, where it sucks sap from the leaf undersides and culms. It is most common during the winter and spring, and disappears during hot summers. It is controlled by ladybeetles. In general, aphids aren’t a major problem since there are so many organisms that prey on them, but they can appear in an occasional outbreak that causes wilting of the leaves and shoots, a reduction in vigor, and stunted growth. They can also transmit fungal diseases, such as black mildew.” Bamboo mites are also common in our area.

University of California at Davis “Giant Whitefly” page mentions a black mold that forms during whitefly infestations.

To determine which insect is invading your bamboo, you may want to take a bagged sample to a Master Gardener Clinic for identification. For information about Clinic hours see their website (Plant Clinic Schedule).

browning of leaves in oakleaf Hydrangea

Why are the leaves of my oakleaf Hydrangea turning brown around the edges and falling off?

We do not diagnose plant problems, especially without a sample. It might be wise to bring a sample to your local Master Gardener clinic. You can locate a Master Gardener Clinic within Washington State here.

However, based on my personal experience with my own oakleaf Hydrangea (Hydrangea quercifolia), it is a semi-deciduous shrub that will hold on to its leaves through winter, only to replace them with fresh growth in the spring. All my Hydrangea’s old leaves have turned reddish-brown and look very ratty. Once new growth resumes in spring, I cut off most of the tattered leaves. (Don’t do it too early, in case there is a late frost.)

If you have new growth, do not worry about your shrub, but if you do not have new growth or it is the new growth that is turning brown then you should take a sample leaf into one of the Master Gardener clinics (linked above).

wilting Gerbera daisies

My Gerbera daisies look marvelous, however, the flowers come up only a few inches and then wilt and fall over, but the leaves look great. There are no yellow leaves to denote over watering. What am I doing wrong? They are planted in the ground.

Ideal growing conditions for Gerberas include the following:

SOIL: A medium that has adequate pore space and yet retains substantial amounts of water should be used. Peat moss and peat-like substances, therefore, are essential ingredients in the preparation of media… The soil pH should be adjusted to between 5.5 to 6.2 for optimal gerbera growing conditions. In very acid soils this can be achieved by adding either limestone or dolomite to the soil mix. It would be hard to get too much organic matter into the soil for this plant. A mixture of one-third sand, one-third leaf mold and peat moss, and one-third rich loam…is ideal.

WATER: Moist well-drained… Gerberas require an abundant supply of moisture, but will succumb under waterlogged conditions.Best grown in areas of long, warm summers and high humidity.

FERTILIZATION: Fertilize lightly but regularly… Fertilizers containing a high percentage of an ammonia-type nitrogen should be avoided.

LIGHT: …Provide protection from the afternoon sun in hot climates (i.e. summer in the Pacific Northwest).

PLANTING: The most important factor in gerbera production is transplanting… Gerberas need to be transplanted with the crown at or preferably above soil level. The crown should be visible at all times, and should be allowed to dry out between irrigations.

If you are doing all of this and the flowers are still drooping, you might want to dig one of the plants up and take it to a Master Gardener clinic. If they do not know what is wrong, ask them to send it to the pathology laboratory in Puyallup. It is better to go through Master Gardeners first so you will not be charged. To locate your nearest clinic, go to the WSU Master Gardener Program website
and click on I Want to Talk to a Master Gardener Volunteer.

Sources:
1. Annuals for Every Purpose, by L. Hodgson, 2002, p. 138-139.
2. International Plant Propagators’ Combined Proceedings, vol. 34, 1984, Gerbera Production and its Problems, by B. Tjia, p. 365-381.
3. American Horticultural Society Illustrated Encyclopedia of Gardening; Annuals, ed. by M. Yee, 1982, p. 101-102.
4. Annuals and Perennials, by editors of Sunset Books, 1993, p. 72.

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).