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Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Continuing education, Potted plants, Container gardening

I am going to create container plantings for some customers, and I wonder if you know the best source (book) for combining plants in containers. Also, where might I take a class in container planting?


The Miller Library has a large number of books in its online catalog on container planting, but here are a few which may be helpful to you:

Container Gardens by Number by Bob Purnell (Reader's Digest, 2004)
Contain Yourself by Kerstin Ouellet (Ball Publishing, 2003)
The Complete Book of Container Gardening edited by Alan Toogood (Quarto Publishing, 1991)
The Book of Container Gardening by Malcolm Hillier (Simon & Schuster, 1991)
A Practical Step-by-Step Guide to Complete Container Gardening compiled by Ideas into Print (Whitecap Books, 1997)

This booklist will give you an idea of the selection of books on the topic.

UW Botanic Gardens occasionally offers classes on container planting, as does Seattle Tilth.

Also, some local nurseries occasionally offer classes. One example is Swanson's Nursery.

Date 2017-01-12
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Plant Answer Line Question

Keywords: Potted plants, Roots, Planting

For how long can purchased plants remain out of the ground?


If the plants are in pots, they can stay out of the ground as long as needed. Keep them watered and they will be fine. But if they are bare root, then you should plant them temporarily (called heeling in) in a trench until you can get them into their proper holes. The most important thing to remember is to keep the roots moist. Keeping the plants out of the sun can help reduce stress as well. If digging a trench is impractical, then cover the roots with damp towels or burlap bags. Of course, planting sooner is better!

Date 2016-12-07
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Plant Answer Line Question

Keywords: Plant nutrients, Citrus limon, Potted plants, Water requirements, Fruit--Care and maintenance

I purchased a small Meyer lemon plant from a nursery in Florence, OR, and it grew, and blossomed very well, and even produced many tiny lemons - all of which have now, at this point, dropped off. The leaves are yellowing, too. It is in a good size container, in full sun. The container sits in a large saucer which does fill with rainwater. This I empty, but the plant remains wet. New blooms are coming on some of the branches, old blooms are shrivelling. No more lemons coming as yet.

My question is, why did the tiny lemons drop off? And, should the plant get overly wet? My nursery person has no information. I would appreciate any information you have.


The following information comes from Citrus (by Lance Walheim, Ironwood Press, 1996).

It sounds as if your container has good drainage, but maybe the plant is getting too much rainwater. That might be causing the leaves to turn yellow. Another cause could be a nitrogen deficiency, which would be most visible in older leaves, which would yellow from the tip to the base.

As far as the plant's water needs, it will need water when the top two to three inches of soil become dry. Frequent watering (or excess rainwater) can leach nutrients from the soil, so the plant will need to be fertilized regularly -- once or twice a month using a liquid, high-nitrogen fertilizer that includes the micronutrients zinc, iron, and manganese.

The small lemons which drop off may not be anything to worry about, as fruit drop occurs normally as the tree varies its fruit load with its carrying capacity. Pea-sized fruit usually drop about one month after bloom. A more noticeable drop occurs in late spring to early summer, when golfball-sized fruit may drop. Other reasons for fruit drop could be conditions which limit tree growth, such as excess heat, lack of soil moisture (not relevant in your case), and fluctuating weather conditions. It is also possible that the fruit drop is due to lack of nitrogen.

Date 2016-12-17
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Plant Answer Line Question

Keywords: Hoya bella, Potted plants, Tropical plants, House plants

My Hoya bella was recently moved outside. It flowered nicely, but now the leaves are a light yellow/green and the soil surface in the pot is covered with moss. What is wrong and what can I do?


Here is some information I found in the book, Subtropical plants: a practical gardening guide (by Jacqueline Sparrow and Gil Hanly, 2002, p. 107), quoted below:

Hoyas do very well in pots. They need bright light, but not sun...Hoyas strike fairly easily from cuttings, taken at the warmest time of the year.

About the yellowing of the leaves...I am pretty confident that this is due to the plant getting too much water (rain, whatever source, while it was outdoors) and the soil not drying out, which also explains what happened to the top of the soil--the moss or algae growth there. I would just gently scrape off the soil surface and put a thin layer of potting soil over it. If the plant starts getting what it needs again (as it did before it was put outdoors), it will hopefully return to its former healthy self.

During its growing season, Hoya bella prefers temps between 64 and 68 degrees; during its rest season, 59 degrees is the recommended minimum temperature (so here in Seattle, right next to a window may be too cold).

University of Florida provides additional information about Hoya bella.

Date 2016-10-26
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Plant Answer Line Question

Keywords: Potted plants, Australian plants, Pruning trees, Eucalyptus

I recently purchased two Eucalyptus gunnii trees and one E. dalrympleana, which are still in their pots. I have them in full sun, facing south. I have been watering them every day - is this appropriate? I know that the gunnii tolerates waterlogged soil.


All Eucalyptus prefer full sun and well-drained soil. They are very drought tolerant when established.
Source: Manual of Woody Landscape Plants, by M. Dirr, 1998, p. 352.

If your plants are in terracotta containers they will need daily water. If they are in non-porous containers you have a bit more leeway, but do not let them dry out while they are young.

Another consideration is whether you plan to grow these trees in containers permanently, or if you are going to be moving them into the garden. If you plan to keep them in pots, bear in mind that these trees will get quite large (70 feet tall by 20 or more feet wide), so you may end up needing to do a lot of pruning from the top as well as root pruning. Sometimes, even when planted out into the garden, urban gardeners with small lots will coppice a tree like Eucalyptus gunnii or E. dalrympleana annually so that it does not overgrow its site, and so that the rounded, juvenile leaves are maintained. See the Royal Horticultural Society's page on eucalyptus pruning for additional details.

If your plan is to move the trees into the garden, it is best to do it when they are relatively young and small, as Eucalyptus generally dislikes root disturbance.

Date 2016-12-02
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Plant Answer Line Question

Keywords: Water-absorbing polymers, Potted plants, Container gardening

I am doing container plantings for clients (some of them big -- the containers, not the clients), and have water concerns. Have you received any feedback on use of those "soil moist" granules that are supposed to cut down on waterings? My fear is that over time, especially with shrubs in a container, there may be some root rot.


Although there is not any conclusive information on whether use of water-absorbing polymers will contribute to root rot in planters, there are quite a few other causes for concern. Local gardener and writer Jessica Salmonson discusses the matter on her web site, Paghat's Garden.
Here is a brief excerpt:

Many of the 'superabsorbent' properties claimed by polymer manufacturers are exaggerated, and during biodegradation these polymers even reverse their effect, depriving plants of moisture. Woodchips, quality compost, or peat do the same job adequately, plus the woodchips or compost provide safe plant nutrients and a medium for beneficial microorganisms such as polymers retard.

And, inevitably, it turns out that some polymers do in fact reach the foodchain, especially the allegedly safer-to-the-environment biodegradable synthetic polymers. These are fed directly to livestock as feed supplements, are dispersed over crops in herbicides & pesticides, & are mixed into garden soils because of preposterous claims of doing away with a need ever again to water the garden.

Extension horticulturist and Washington State University Professor Linda Chalker-Scott has also written on this issue, and states that even beyond the health and environmental concerns, hydrogels do not work well in clay soils, and can decrease a plant's ability to absorb essential nutrients.

Local garden writer Ann Lovejoy writes about a non-polymer alternative in this article in the Seattle Post Intelligencer: "The newest such water holder I've tried is called Quench. This is a granular, sand-colored material that turns cloudy-translucent in water. Unlike polymers, Quench is based on a natural material (cornstarch) in a form that can absorb up to 400 times its weight in water, right up there with good compost or forest duff. Unlike the usual polymers, this stuff lets go with grace. About 95 percent of the stored water is released to plant roots in midsummer, making plants a lot less dependent on people in hot weather."

Date 2016-10-29
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April 11 2017 13:50:16