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Elisabeth C. Miller Library

Keyword: Drought-tolerant plants

Beth Chatto’s Gravel Garden

One of my favorite books in the Miller Library collection is Beth Chatto’s Gravel Garden. Published in 2000, it recounts the development of a formerly grassy parking area into a garden with gravel used as mulch, and no irrigation once plantings were established.
I visited the Chatto garden in August 2000 when the garden was in its eighth season. I was charmed with the concept and especially the look of the garden. When I learned a book was coming out, it was a must not only for the Miller collection, but also for my home library.
Beth Chatto (1923-2018) was an early proponent of the concept of “right plant, right place,” choosing plants with needs that match the conditions of their garden setting. Gravel Garden is a careful study of what plants have worked in this new garden, and those that have not.
Your mental image of England may be of green meadows and lush gardens nurtured by gentle summer rains.  However, this garden is in Essex, one of the driest counties, and averages only 20” inches of rain per year. By contrast, Seattle has nearly twice that amount. One key difference is the rainfall is distributed evenly through the months, so that the long, droughty summers we experience are not typical there.
Sadly, this may be changing. In June 2023, I attended the Hardy Plant Study Weekend at the University of British Columbia in Vancouver. John Grimshaw, noted author and director of the Yorkshire Arboretum, reported that precipitation throughout the eastern part of England has been diminishing, and summers are drying out.
Last summer was especially bad and the Beth Chatto Garden blog reported that as of mid-August 2022, it had been two months without any rain. A similar drought occurred in 1995. In the book, Chatto describes at the end of that summer “a dry look to this area, but not a dead look.” She continues, “I am often thankful to see how many plants not only survive but look good after this testing period of drought.” A list of the successes, and the few failures, follows. I consult it frequently.
Reviewed by Brian Thompson.

Watering Salvias

I recently planted several purple Salvia plants that have completely faded from beautiful, bright purple to beige. It has been really hot and dry and I’ve been watering them in clay soil once to twice a day. Is it possible that I’m overwatering them? Or do they need even more water since they were just planted?

 

I’m not sure what type of Salvia you are growing, but it is possible you are overwatering them. The heavy clay soil combined with watering 1-2 times daily sounds like too much for a plant that is drought-tolerant once established. To learn more about growing ornamental salvias, see this University of California, Davis Arboretum Review, #44, Fall 2003 article, “Salvias for Every Garden” by Ellen Zagory.

I would suggest watering less often, but watering more deeply, and possibly mulching around the plants. Some xeriscaping resources suggest using gravel, and it is mentioned in “Landscape Water Conservation: Principles of Xeriscape” from New Mexico State University Extension, with the caution that although “some plants native to very well drained soils grow better in gravel mulches […] rock mulch becomes very hot in our climate and can injure or limit growth of some plants. Ultimately, the mulch should be shaded by landscape plants that will provide environmental cooling. Using gravel mulch alone as a landscape element may result in increased home cooling bills and require greater weed control efforts.”

This article by Seattle-area garden writer Ann Lovejoy on drought-tolerant gardening may also be of interest.

 

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growing under Thuja

I have a large Western Red Cedar (Thuja plicata, I think!) under which grow a few weeds but not much else. I would like to find a low maintenance solution for the ground that won’t do any harm to it. Ground cover? Pea gravel? I worry that the shallow root system can be easily smothered so that adding soil and plants is not a good idea, plus the roots are a dense mat and difficult to dig through. Do you have any ideas or suggestions? What native plants might grow under the tree and how can I get them established?

 

As you’ve realized, Western red cedars have a dense mat of roots close to the surface. It’s not a good idea to add soil on top of the roots of trees because their root flare should remain above the soil — and even if you did, the roots of cedars would spread into that soil in a short period of time. It’s also important to keep in mind that under natural conditions the ground beneath Thuja plicata is usually bare of other plants.

If the area beneath your tree isn’t in deep shade and has at least some sun, you could plant spring ephemerals, including bulbs. They emerge in spring when the soil has plenty of moisture, then most die back before our summer droughts. They’re not difficult to plant under large trees because you don’t need to dig a large hole for seeds, bulbs, or small bare-root perennials. Good choices are Anemone blanda, Aquilegia (Columbine), Corydalis lutea, Crocus, Galanthus (snowdrops), Iris reticulata, and various kinds of Narcissus, including daffodils. Most tulips are not long-lived in our area. Hardy Cyclamen emerge and flower at other times of the year, but they’re also an excellent choice. Unfortunately, most of these plants are summer-dormant, when you’ll probably be out in your garden, and some self-seed prolifically under ideal conditions. A valuable resource, available for checkout at the Miller Library, is Planting the Dry Shade Garden, by Graham Rice (2011). Some of the plants he recommends will require regular watering under cedars.

Another option, also feasible if your area has some sun, is to plant our native Western sword fern (Polystichum munitum). It’s evergreen, so has a presence all year, and is the most sun and drought tolerant of our native ferns. I have a 60 foot red cedar in my garden, and have successfully maintained sword ferns beneath it in partly sunny areas, but not in deep shade, where they’ve died out. However, because they won’t survive our summer droughts in nature under these conditions, I’ve needed to water them about every 3 weeks in order to keep them alive. I’ve planted fairly small plants and watered them more often than that during their first year. If your soil is very sandy, sword ferns might not do well.

If you require a reliably showy solution, staging large planters planted with annuals or perennials, shrubs and/or trees might be best. The plants you choose will depend upon how much sun the area receives. Of course, they’ll need to be watered regularly, but large planters don’t need watering as often as small ones. If your hose-bib is not too far away, installing drip irrigation on a timer will ensure that your plants survive when you’re away from home.

drought-tolerant native grasses

I am looking for a native, drought-tolerant grass for a small garden plot in Seattle. Can you suggest a grass that is 2-3 feet tall and at most 2 feet wide.

Native grasses that will do well in a dry meadow setting and grow 2-3 feet tall are:

Festuca idahoensis, Idaho fescue
Bromus carinatus and Bromus marginatus, brome grasses
Elymus glaucus, wild rye grass
Melica species, onion grasses
Calamagrostis nutkaensis, Pacific reedgrass

Each of these grasses grow in very distinct shapes–I recommend that you look at them before choosing which species to plant. Fescues are popular grasses for gardens because of their fine blades and pretty seed heads. Additionally, the Elymus and Bromus will grow much more quickly than the other species.

You can perform searches on each of these species at the USDA Plants Database by typing the plant name into the Plants Name search box–this database will give you additional information about the species and some pictures.

The Washington Native Plant Society website has a list of native plant vendors.

planting over septic drain fields

I am looking for plants suitable for a septic drain field site. I have a very large north facing slope in open sun with a drain field running along the top half. I would like to plant low to no maintenance ground covers and low growing shrubs to cover this area. This is a focal point when driving up to my house so I want it to be eye catching and interesting year round.

I thought of heaths and heathers as a possibility, but I’m not sure if the root system is shallow enough. I also would like to include native ground covers such as ferns, Gaultheria shallon and any others that you might think would work, as well as ornamental grasses and perennial flowers for interest. Can you please offer a resource for planting over drain fields or a list of plants that you think would work?

 

Trees or large shrubs should be kept at least 30 feet away from your drain field. If you do plan to plant trees near a drain field, consult an expert to discuss your ideas and needs. Trees and shrubs generally have extensive root systems that seek out and grow into wet areas like drain fields. Grass is the ideal cover for drain fields. Grasses can be ornamental, mowed in a traditional lawn, or left as an unmowed meadow. You can also try groundcovers and ferns.

The key to planting over the drain field is to select shallow-rooted, low-maintenance, low-water-use plants. When tank covers are buried, keep in mind that plantings over the tank–from inlet to outlet–will have to be removed every three or four years for inspection and pumping.

Planting your drain field will be much different from other experiences you may have had landscaping. First, it is unwise to work the soil, which means no rototilling. Parts of the system may be only six inches under the surface. Adding 2 to 3 inches of topsoil should be fine, but more could be a problem. Second, the plants need to be relatively low-maintenance and low-water use. You will be best off if you select plants for your drain field that, once established, will not require routine watering.

SOURCE: WSU Cooperative Extension – Clallam County

Information can be found here.

Thurston County, Washington, has some information about landscaping a drain field, including plant suggestions, here.

Additionally, the Pacific Northwest Gardener’s Book of Lists (1997, by R. & J. McNeilan) offers a number of groundcover lists for various situations, including groundcovers for dry sites, slopes, and sun and shade. The Miller Library has this book.

selecting lawn grasses for the PNW

I’m looking for a type of lawn grass that is fairly drought-tolerant and will do well in our area (Seattle). Any suggestions?

 

One of the best resources for local information about lawn seed selection and general maintenance is David McDonald’s Ecologically Sound Lawn Care for the Pacific Northwest. It is available in print form as well as online from the City of Seattle. In it, he recommends a mix of turf-type perennial ryegrasses and fine fescues (such as chewings, creeping red, and hard fescue) for their flexibility in a range of local garden conditions. Ryegrasses thrive in full sun, and fescues take sun but will tolerate some shade. He also suggests ecolawns (sometimes called ecoturf) which mix grasses, clovers, yarrow, daisies, and other small flowering plants, because they tolerate dry sites, do not need fertilizer, and generally require only monthly watering. They also need mowing less frequently.