rusty leaves on Asters

Our Asters are green and getting ready to bloom but the
lower 8″ are “rusty” or burnt looking. Did our bark mulch hurt them? Too much
fertilizer? This is their third year in the same spot.

There are quite a few potential causes of the rusty leaves you are
seeing. It might be entirely normal, as mature Asters (renamed Symphyotrichum) can start looking a bit ragged in late summer. It could be due to excessive heat,
overwatering (symptoms include yellowing and dropping of lower leaves),
or fertilizer burn (Asters are sensitive to soluble salts in chemical
fertilizers). It could be a fungal disease, rust, or Aster yellows, a
common disease caused by a microscopic organism (phytoplasma) and spread
from plant to plant by leafhoppers. With Aster yellows, you would notice
a loss of green in the leaf veins, and yellowing of new leaves.
Sometimes, infected outer leaves turn a rusty or reddish purple color. A
good general practice to keep your Asters looking full and less leggy is
to cut them back by one-half to two-thirds when they have reached 12 to
16 inches in late spring/early summer. (Source: The Well-Tended Perennial
Garden by Tracy DiSabato-Aust, Timber Press, 1998).) Here are
links to resources which describe other possible causes of the leaf
problem.

Connecticut Agricultural Experiment Station

Missouri Botanical Garden

To determine the exact cause, it might be worth bringing a sample to a
Master Gardener Clinic.

on replanting seed potatoes

I would like to plant a second crop of potatoes in July. Could I use
potatoes dug from my first crop this year or should I try to find seed
potatoes?

You can plant mid-season and late potatoes this month, but there are
particular varieties that are best suited to planting at this time. This
is one reason not to plant the potatoes you just dug (which are
an earlier variety).

Here are links to additional information:

From the University of Illinois Extension.

Growing Potatoes in the Home Garden from UC Santa Cruz.

Steve Solomon’s Growing Vegetables West of the Cascades (Sasquatch Books,
2000) says that because of the large number of viruses which can affect
potatoes, you should not carry over your seed (replant). It is safest to
use certified virus-free planting seed. He says that your crop might be
fine the first time you replant your own potatoes, but they will become
increasingly susceptible to viruses.

on pruning flowering bulbs

This is my first year planting spring flowering bulbs, which
grew nicely. I cut the dead flower and the stalk once it died back, and now the
foliage is yellow. What am I supposed to do with the yellow foliage? Pull it out? Cut it off? Just leave it alone? Also, will
planting some annual petunias now hurt the bulbs I have planted in the
garden? How close can I plant the petunia to the bulbs? I was going to
try and hide the yellow foliage.

The answer will depend on which bulbs you were growing. For example,
daffodil stems should not be cut back until at least 6 weeks after the
flowers have faded, and you should never tie the foliage in knots or
braid it (this is a common but ill-advised habit). You can leave
daffodils in the ground to naturalize and spread.

With tulips, you also need to wait at least 6 weeks from the fading of
the flowers before cutting back the leaves.

With hyacinths, you can pull away dead foliage and flower stems as they
fade. When the top growth has died down, you can either leave them in the
ground or dig up the bulbs, dry them off, and store them for replanting.

If you are growing iris, you can cut the dead flower stems to the base,
and cut away dead leaves in the summer. If they are bearded iris, the
fan of leaves may be cut back in the fall to about 8 inches above the
base.

(Source: The Plant Care Manual by Stefan Buczacki, Crown Publishers,
1993)

You can certainly plant your annual petunias quite close to bulbs like
daffodils and tulips and other bulbous plants which are quite vertical.
Just don’t plant right on top of the bulbs. To disguise dying bulb foliage, use perennial ground cover plants that keep their leaves over the winter, and that have stems soft enough for bulbs to emerge through them. Hardy geraniums (true geraniums, also called cranesbill) and creeping veronica, such as Veronica peduncularis ‘Georgia Blue,’ are good choices. You can remove dried leaves as needed, and they can be tidied or groomed in early spring.

on amending clay soil

I have typical Seattle clay soil and I want to amend it before planting. I’m re-grading a large (~2000 sq. foot) area and have already added copious amounts of mulch, compost, overturned sod, etc. I’m planning on planting a cover crop of clover this summer, but before doing so thought it’d be a good idea to till in some sand. I was thinking about a level inch over the whole yard before tilling. Is there a particular chemical composition to use or avoid? How about grain size?

You may find this information from Colorado State University Extension on soil amendments useful. Excerpt: Don’t add sand to clay soil–this creates a soil structure similar to concrete.

Professor Linda Chalker-Scott of Washington State University also debunks
the idea of adding sand to improve clay soil.

For good advice on amending the soil, see these links:

Building Fertile Soil and Choosing and Using Cover Crops for the Garden and Orchard from the University of California, Santa Cruz Agroecology Program.

Growing Healthy Soil from Seattle Public Utilities.

It sounds to me as if you have already taken great steps toward improving
your soil, and adding sand not only will not be necessary, but would not
be a good idea.

trees for privacy

I need a large tree for privacy and would like it to be fast growing here in Seattle. I would not like it to be much more than 15 feet wide at maturity but the height doesn’t matter, also evergreen. Would an Incense cedar grow fast?

In addition to Calocedrus decurrens (Incense Cedar), you might also consider Podocarpus or Cryptomeria.

You may want to consult the locally created web pages of Great Plant Picks, and see which evergreen trees they recommend for our area. This is their list of conifers, and here is the information on Incense Cedar.

Incidentally, Great Plant Picks says that Incense Cedar does make a good screening plant. They claim it will mature at 35-40 feet tall in garden conditions (as opposed to in the wild), and about 10 to 12 feet wide, so your original idea of planting this tree sounds like a good one.

native Northwest beach grasses

I live in a community on Camano Island. We have some communal beach front property and would like to plant some native beach grasses that are about one foot high. What species do we have to choose from and where can we purchase them?

I found a list of native Northwest beach grasses in an online symposium moderated by Alfred Wiedemann of Evergreen State College in Olympia. (The symposium was about an invasive species, Ammophila arenaria, or European beach grass, which has been crowding out native species.) Here are some of the plants he mentioned:

Elymus (Leymus) mollis (Dunegrass)

Abronia latifolia

Convolvulus (Calystegia) soldanella

Carex macrocephala

Glehnia leiocarpa

Lathyrus littoralis

Poa macrantha

Here is a Seattle Times article from May 1, 2005 about beach plants by Valerie Easton that may be of interest to you. The Miller Library has the book that is mentioned in the article, Native Plants in the Coastal Garden by April Pettinger (Timber Press, rev. and updated, 2002), and it includes a list of native grasses. These two grasses were specifically recommended for beachside gardens:

Elymus or Leymus mollis (also listed above)

Festuca rubra (Red fescue)

Washington Native Plant Society might also be a good resource for you. They provide a list of nurseries in our area which specialize in native plants. King County’s Native Plant Guide also has a list of sources.

on picking avocados

What causes an avocado to have a foul taste even when it looks superficially just fine? I’d like to know if there is a way of telling simply by looking at them, so I can avoid buying bad ones.

According to the book, Fruit & Nuts by Susanna Lyle (Timber Press, 2006), there are three main varieties of avocado: Mexican, Guatemalan, and West Indian. Mexican fruits tend to be smaller, with thin skins that turn a glossy deep green when ripe. Guatemalan fruits are round or pear-shaped and have pebbled skin. The largest avocados are West Indian, nearly round, with shiny green skin and flesh that is less rich in oil.

Avocados tend to take a long time (sometimes over a year) to reach maturity from the beginning of fruit-set, and sometimes they will not soften and become edible because the stems have a ripening inhibitor. For this reason, they must be picked while still hard, and then allowed to ripen at room temperature. Mexican fruits ripen fastest (6-8 months) but have a shorter storage life. Guatemalan fruits take 12-18 months to ripen and must be stored at about 10 degrees Fahrenheit for over a month.

This factsheet from U.C. Davis about post-harvest quality in avocados describes optimal storage temperatures, and mentions several variables that can lead to an unpleasant flavor:

On-tree storage may result in development of off-flavors or rancidity with overmaturity
Off-flavors may also develop when fruit are harvested during periods of hot weather
>10% CO2 may increase skin and flesh discoloration and off-flavor development, especially when O2 is <1%
Anthracnose: Caused by Colletotrichum gloeosporioides and appears as the fruit begins to soften as circular black spots covered with pinkish spore masses in later stages. Decay can penetrate through the flesh and induce browning and rancid flavor.

There are several scientific articles that discuss heat-induced off-flavors. In one example, “Isolation of Unpleasant Flavor Compounds in the Avocado (Persea americana)” by Brian I. Brown, certain varieties seem more prone to bad flavors than others, and some varieties lose the off-flavor once they are fully ripe.

I’m afraid there does not seem to be an easy way to know in advance which avocados will taste bad. Certainly, you should avoid fruits with dents or obvious discoloration in their skin. You might also complain to the market where you have purchased inedible avocados, and they can relay that information to their distributors and see if it has something to do with how the fruit is harvested or stored.

growing conditions for Avocados

We know avocados like dry soil, but are there specific guidelines to follow?

“Growing conditions: Give avocado direct light; insufficient light will cause spindly growth. Provide a warm temperature and medium humidity. Keep the soil evenly moist but not wet and soggy. Fertilize once a month throughout the year… Use an all-purpose soil mix for repotting… Avocado is vulnerable to aphids, mealybugs, scale insects and thrips.”

Source: The Time-Life Gardener’s Guide; Foliage Houseplants, 1988, p. 125

“Growth habit: The avocado is a dense, evergreen tree, shedding many leaves in early spring. Growth is in frequent flushes during warm weather in southern regions with only one long flush per year in cooler areas.”

“Foliage: Avocado leaves normally remain on the tree for 2 to 3 years.”

Source: California Rare Fruit Growers Association website

plants and spontaneous combustion

My “gas plant,” Dictamnus albus, is finally flowering for the first summer ever, and I am starting to worry: can it spontaneously combust? It’s planted close to the house. I remember stories from a couple of years ago about houses in Seattle catching fire because of sun or extreme heat igniting compost or soil in planters. Are there plants besides Dictamnus that are especially flammable?

Dictamnus is not called the gas plant or the burning bush for nothing. It is in the same family as citrus plants, and contains extremely volatile oils that can indeed reach a high enough temperature to ignite. In Defense of Plants blog describes this aspect of the plant, and asks why a plant might have this capability (to burn out competing vegetation, or merely an unintended consequence of oil production). Excerpt:
“If air temperatures get high enough or if someone takes a match to this plant on a hot day, the oils covering its tissues will ignite in a flash. The oils burn off so quickly that it is of no consequence to the plant. It goes on growing like nothing ever happened.”
Some gardeners amuse themselves and amaze their friends by demonstrating this flare of flame, but I highly recommend you not try it if your plant is up against your house!

You can read more about the flammable properties (and garden merit) of Dictamnus in the June 1995 issue of American Horticulturist. See the article “Ignite the Night” by Robert L. Geneve.

There are other flammable plants. Areas that are accustomed to preparing for summer fire season (such as Grants Pass, Oregon and Ashland, Oregon) have information about which plants are most (and also which are least) likely to ignite. The flammable list includes ornamental juniper, Leyland cypress, Italian cypress, rosemary, arborvitae, eucalyptus, and some ornamental grasses.

If you are concerned about the proximity of this plant to your house, you might consider transplanting it elsewhere in fall, though be aware that Dictamnus has a taproot and is not fond of being moved.

on growing heirloom fruit varieties

I am interested in planting fruit trees on our treeless property. Can you recommend any sources of bare-root heirloom fruit varieties grafted onto modern rootstocks? Or do people who grow heirloom fruits usually use the old rootstocks, too?

I am also interested in finding a descriptive list of how different heirlooms taste, how difficult their pests are to control, and how they do in our region (Puget Sound).

Below are some suggestions:

1. WSU’s fruit research station in Mt. Vernon is the best place to learn about history, grafting rootstocks, varieties, etc. Here is an article from the spring 2013 issue of WSU’s Washington State Magazine on heirloom apples.

2. There is an event in early October at Cloud Mountain Farm in Everson, Washington. They have a fruit festival where you can taste the fruits and talk with experts.

3. An outstanding book you will probably want to buy (or come to the library to review it first) is Fruit, Berry and Nut Inventory, 4th edition, An Inventory of Nursery Catalogs Listing All Fruit, Berry and Nut Varieties Available by Mail Order in the United States. Edited by Ken Whealy, 2009.

We also have many other excellent reference sources about growing tree fruit.

4. You might consider joining the Western Cascade Fruit Society or the Seattle Tree Fruit Society. They offer courses and events, and are very knowledgeable.

5. The staff at Raintree Nursery near Morton, WA offer a wealth of information about what grows well in the Pacific Northwest, best rootstocks, etc.