managing crabgrass

I used to have a pristine green lawn and it has since been overtaken by crabgrass. I’ve tried organic and chemical weed-and-feed products to no avail. What can I do to get the weeds out?

Local plant expert Arthur Lee Jacobson has written about crabgrass (Digitaria sanguinalis) in his book, Wild Plants of Greater Seattle (2008): “Crabgrass is difficult to get rid of because it seeds itself at an almost unbelievable rate; mowing simply makes if flower nearer to the ground. Control demands diligent weekly hoeing and pulling by hand, from July through at least September. Even a few specimens left to reseed ensure more seedlings next summer.”

According to Ecologically Sound Lawn Care for the Pacific Northwest by David McDonald (Seattle Public Utilities, 1999), weed invasions are best prevented by making a habit of aerating and topdressing to correct soil compaction and build fertile soil. He recommends that you “overseed at summer’s end with locally adapted grasses to fill bare areas with grass rather than weeds. Correct acidity or poor drainage. Mow higher (2-2 1/2 inches, or 1 inch on bentgrass), fertilize moderately with slow-release or natural products, water deeply and infrequently in the summer. Tolerate some broadleaf plants like clover and daisies. Hand weed or spot-spray problem weeds in spring or fall to stop them before they spread.”

There is additional information on crabgrass from University of California, Davis Integrated Pest Management.

Seattle Public Utilities has information on best practices for maintaining a healthy lawn.

Toxic-Free Future (formerly known as Washington Toxics Coalition) also has a helpful lawn care fact sheet that might be helpful to you.

Since the weed-and-feed approach to the problem was not effective (and chemical weed and feed should be avoided), I recommend trying some of the cultural controls discussed above (mow higher, only fertilize at appropriate times and don’t use quick release fertilizer, water less often but more deeply, improve drainage by aerating, build soil by mulching). Solarization might be an option if the problem can’t be addressed by hand-weeding combined with the other methods described.

sowing herb seeds in July and August

Are late July and early August still a good time to start sowing seeds for basil, parsley, and coriander in Seattle?

According to Winter Gardening in the Maritime Northwest by Binda Colebrook (Sasquatch Books, 1998), you can sow coriander in late August to early September and as long as the winter is not too harsh, you should have success. You may want to keep the plants under cover during winter.

When you sow parsley, Colebrook recommends looking for European varieties which are cold-hardier than the American type. The following article, from the British paper The Guardian (July 1, 2006 issue) discusses summer sowing:
Summer-sown parsley by Sue Stickland

Here is an excerpt:

“Spring-sown parsley often struggles, but sow now and it’s easier to get healthy plants. These should give a good crop right through to autumn, and look as decorative in beds, pots and troughs as they do on the plate.

Sow directly where it is to grow, or into small pots for transplanting, and keep it moist. In steady July temperatures, germination should take a couple of weeks (quicker by half than in spring). Plant out seedlings from pots as soon as they are big enough, and before the ‘tap’ root hits the bottom. This will give stronger, more resilient plants.

The main enemies of spring-sown parsley are aphids and carrot flies. Aphids not only make the leaves unappetising, but carry viral diseases; carrot flies tunnel into the roots, weakening the plant, just as they do with their main vegetable host. When parsley starts to yellow and redden, and plants become stunted, one or other of these pests is usually to blame. July sowings avoid the worst attacks, provided you keep them well away from any ailing plants. Never try to grow this herb in the same spot twice.

For vibrant, deep green leaves, the plant must also have rich soil and plenty of moisture. Add well-rotted manure or garden compost (or a bagged equivalent) to a garden patch, and to the potting compost in deep troughs and pots. Don’t forget them in dry spells – most herbs won’t need watering, but parsley will. When it turns cold, bring pots into a cold frame, greenhouse or other warm, protected spot. These late-sown plants will provide welcome fresh sprigs in winter and early spring.”

Basil is a half-hardy annual, and is best sown into pots in early spring, or directly into the garden in late May. I don’t think you can successfully grow an outdoor fall/winter crop. Mary Preus, author of The Northwest Herb Lover’s Handbook (Sasquatch Books, 2000), suggests potting up plants from your garden in September and moving them indoors. If given the right light and care, you can keep harvesting throughout the winter.

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.”