Hibiscus plant care and pruning

How do we prune a Hibiscus tree that is about 3 feet tall? The plants are located in a container outside of our senior center. They wintered inside and are now too bushy at the top. How do we prune so they are more compact? What is the correct way to care for these wonderful flowering trees?

It sounds like you have Hibiscus rosa-sinensis—the tropical evergreen shrub. Late spring is the time to prune. According to the American Horticultural Society Pruning & Training book: Prune established plants by cutting back main shoots by as much as one-third, and shorten laterals, leaving two or three buds. Dead wood attracts canker, so it should be removed promptly. To renovate completely, remove older branches entirely and cut the remainder back hard. The response is usually good, but if most stems have died back, it is best to replace the plant.

(Source: American Horticultural Society Pruning & Training, ed. by C. Brickell, 1996, p. 201).

Other pruning information is available from Hidden Valley Hibiscus.

Also, my personal experience with a 10-year-old Hibiscus is that pinching out tips of stems in spring and summer increases flower production.

Growing avocado plant indoors

We have a large avocado plant (indoors) that is mystifying us. A couple months ago, it shed most of its leaves. The leaf would get droopy and the tips of the leaves would turn brown and dry out and then spread up the leaf. It got down to its last seven leaves and then seemed to stop, although all of these leaves have varying degrees of this leaf tip burn. Now over the last month or more, small new growth is appearing. They have not grown much at all and are only about an eighth of an inch long.

When growing an avocado (Persea species) indoors, you will need to be sure it is getting enough light. It is normal for the plant to drop older leaves. You should also keep the plant in a cool spot. According to The Houseplant Expert by D. G. Hessayon (Expert Books, 2001), your plant will do best if you repot it annually and pinch the tips to encourage bushy growth. Lee Reich discusses growing avocados indoors in an article (now archived) for California Rare Fruit Growers. Here is an excerpt:

“Indoors, avocado plants are often gangly and sparse with leaves. One reason for the plant’s gawky appearance indoors is light. Lack of sufficient light causes stems to stretch for it. Another reason is that avocados shed many buds along their stems, buds that might have grown into side branches. The result is a plant stretching out for light, sending out new growth mostly from the tips of the branches and shedding old leaves.

There are several things indoor gardeners can do to keep their plants more attractive. Most obvious is to give an avocado tree bright light. Also, the stretch for light is exaggerated when warmth stimulates growth, so the ideal spot for the plant is at the brightest window in the coolest room. Beyond that pruning back a stem or pinching out its growing tip stimulates branching by awaking dormant buds (not all are shed) further down the stem. There is nothing that can be done about the shedding of older leaves.”

Grown outdoors in an agricultural setting, avocado plants sometimes get leaf tip burn from salt accumulation, as this article from California Rare Fruit Growers explains. If you are using especially salty tap water or overfertilizing your plant, that might be causing the burnt leaf tips. Other causes could be lack of water, too frequent light watering, or poorly draining soil.

Regulating plant growth

I have a Japanese privet that has turned into a 30-40 foot tree next to my patio. How can I get it to stop blooming and dropping its flower and seeds onto my patio? Is there a hormone or something that I can use to regulate plant growth, similar to what is given to olive trees to stop them from producing?

There is a product called Florel which is an organophosphate pesticide that has been used to regulate plant growth. The active ingredient is Ethephon which has some health concerns, as described by the Environmental Protection Agency.

Florel was described as an alternative to the toxic chemical, NAA (Naphthalene acetic acid) which has traditionally been used to thin fruit, in an article in Arboriculture, by Harris, Clark and Matheny, 2004, p. 403). However, Florel is still a toxic product and overuse can damage your plants.

Another (non-toxic!) option would be to remove the privet and plant something which will not interfere with your enjoyment of the patio.

Deppea splendens plant culture and care

I have a plant, Deppea splendens, purchased through a special offer from Pacific Horticulture. It is a native of Mexico. This year (I’ve had it for about 2 years) it looks very healthy and has gotten quite a bit bigger. It is supposed to flower, but it has yet to do so for me. Any answers?

Deppea splendens is such a rare (previously almost extinct) plant that none of our standard sources have any cultural information. However, there was an article written about it in the April 2000 issue of Pacific Horticulture by Kathy Musial which mentions that it needs a frost-protected spot if it is to flower. The article recommends growing it in a container in colder regions so it may be brought into a sheltered area. Overly dry conditions will also cause the flowers to abort.

Excerpts from the article are included in University of British Columbia Botanical Garden’s “Botany Photo of the Day” web page.

recycling or putting plants up for adoption

Do you know of a website or referral service for “recycling” plants? I have about 10 feet of barberry (Berberis) bushes that I want to get rid of and thought if they could be dug up with enough of the roots, someone could use them. They are quite ornamental, birds love them, and the thorns are quite lethal (for me, not the birds).

You can contact Plant Amnesty’s Adopt-a-Plant program.
You can also try GardenWeb’s Pacific Northwest Garden Exchange, or freecycle. You might also see if there is a “Buy Nothing” group in your area which you can join.

flower arrangement tips

What is the right proportion of cut flowers to create a nice arrangement in a vase? Can you give me some other suggestions about flower arranging?

This Brooklyn Botanic Garden article, provides some helpful tips on different aspects of flower arrangement. Here is an excerpt from Cut Flower Care by Rose Edinger:
“The height of the flowers should be in proportion to the size of the container—that is, the height of the flowers should not exceed one and a half times the height of the container.”

The Miller Library also has many books about flower arranging, two of which I’ve listed below:

Flower Arranging from the Garden (1989), by Daphne and Sid Love
The Complete Guide to Flower Arranging (1995), by Jane Packer

common pests and diseases affecting Japanese maples

I have a lovely, 3-ft. Japanese Maple (Acer palmatum) that has access to full sun. I am guessing it is over 3 years old at least. The tree is leafing beautifully, but last week I noticed there are “pustules” all over the stems and branches. They are yellowish-brown in color and somewhat mottled looking. They form in irregular clusters along the branch. Each pustule is about the size of a ladybug; in fact, at first I thought they were beetles, but they do not move and when I removed one, it was liquid-y inside and left a thin, white streak along the branch. I am a beginner homeowner, so I do not know what this is. Do you have any ideas? What can I do to treat this? I would hate to lose my Japanese Maple.

The best way to determine if your tree is diseased is to bring a sample to a Master Gardener Diagnostic Clinic and ask a Master Gardener to diagnose it for you. This service is free to home gardeners.

What you describe sounds like several quite different problems (canker, or scale, for instance), which is why having a hands-on diagnosis is so important. Below is general information about maple diseases which you can compare with your tree. Additionally, I recommend the book Japanese Maples by J.D. Vertrees and Peter Gregory (Timber Press, 2009). It has sections on the most common pests and diseases affecting Japanese maples.

This page from the University of California Agriculture and Resources about Maples includes an extensive list of diseases and disorders that affect maple trees.

Clemson State University has a factsheet on Maple diseases and insect pests (read the entry on scale).

Try searching for “maple” in Pacific Northwest Guide to Plant Disease Control, and compare the descriptions to see if any ring true with what you are seeing. Ultimately, though, the best thing is to get a hands-on diagnosis from the Master Gardeners, as mentioned above.

grafting a walnut scion onto a maple

Is it possible to graft a walnut scion onto a maple tree?

The book, Plant Propagation edited by Alan Toogood (American Horticultural Society/DK Publishing 1999) says that Juglans regia and Juglans nigra, grown for their edible nuts, are usually whip-and-tongue grafted. You would “use a slightly narrower scion than the stock so the thinner scion bark will align with the stock’s cambium more easily.”

I was not able to find any information on grafting a walnut scion onto a maple, but here is an article (pdf) on by William Reid, which has detailed information.

This publication from the University of Georgia College of Agricultural & Environmental Sciences, entitled “Propagating deciduous fruit plants common to Georgia” (1999) indicates that whip grafting or ring budding will work best for walnuts.

Philadelphus lewisii habitat and care

What is the specific habitat of the Philadelphus lewisii (wild mock orange)?

What does this plant need from the habitat in order to survive?

What range does the Philadelphus lewisii grow in?

What family is it in?

What other plants does it often grow around?

What specific habitat does it need?

Where does it grow?

Is it an annual or a perennial plant?

Philadelphus lewisii is a Northwest native, a common shrub east and west of the Cascades. According to Trees and Shrubs for Pacific Northwest Gardens, 2nd edition by John A. Grant and Carol L. Grant, it will “thrive in almost any garden soil in either full sun or partial shade, and are of the easiest possible culture. The hybrids respond noticeably to generous cultivation , fertilizer, and water. (It belongs to) the group of summer-flowering shrubs that are best pruned immediately after flowering.\”

Philadelphus lewisii is a deciduous shrub (in other words, it is not an annual and, although it has a long life span, it is not like an herbaceous perennial that completes its life cycle and starts over the next spring–it is a woody deciduous plant which loses its leaves in winter). (Source: The Royal Horticultural Society A-Z Encyclopedia of Garden Plants, edited by Christopher Brickell; Dorling Kindersley, 1996).

Here is a link to a page from the Washington Native Plant Society about Philadelphus lewisii and its habitat.

It is a Northwest native (state flower of Idaho), and grows throughout Western North America (from British Columbia south to Oregon), southern Europe, and eastern Asia.

The genus Philadelphus grows in rocky woods, semi-desert, and open areas in wet forest. In gardens, it prefers loamy soil and moderate sun.

The genus Philadelphus belongs to the Hydrangeaceae family.

shrubs or trees that provide privacy screens

What shrubs or trees will grow quickly to provide a privacy screen above the 6 foot fence between me and my neighbor? My back yard is only about 20 feet from house to fence, and the first 10 feet is a concrete patio.

The classic fast-growing evergreens for hedges are Thuja ‘Green Giant’ or Leyland cypress (x Cupressocyparis leylandii), but they are a bit boring and because they grow so fast (1-3 ft/yr) it can be a big chore to keep them at a reasonable height. These trees do not stop at 8 feet, but could get to 30-50 feet.

Another fast evergreen is Pyracantha (Pyracantha crenatoserrata to ~8 feet). It is a shrub, but is easily trained/pruned to grow flat. In the past Forestfarm nursery in Oregon has sold both of these, as do most large nurseries. Be aware, however, that this shrub has fierce thorns!

Various types of bamboo could be an option for a fast screen, but plants may be expensive and running bamboo species MUST have a root barrier installed.