Plant Answer Line questions and answers.
Is there a list of the more cold hardy Alstroemerias?
Here is some general information on Alstroemeria from North Carolina State University Extension, which indicates they are generally hardy to 23 degrees.
The Royal Horticultural Society’s A-Z Encyclopedia of Garden Plants, edited by Christopher Brickell (DK Publishing, 1996) says Alstroemeria aurea and A. ligtu and their hybrids are able to tolerate brief drops in temperature to 5 degrees Fahrenheit.
Can you all give me some recommendations for plants that will form a tight hedge? I want a fast growing plant that does not get more than 2-3 feet tall and 2-3 feet wide. I do not want boxwood. Evergreen with glossy leaves is preferable; flowers do not matter to me.
I collected some information from websites and a couple of books for you. I am making one other plant suggestion, and it is the last item.
Euonymus japonicus ‘Microphyllus’
Ilex crenata ‘Northern Beauty’ is described on the website of Great Plant Picks
Ilex glabra ‘Shamrock’
See Missouri Botanical Garden for information and an image.
This can be grown as a dense hedge. It can reach about 8 feet, but takes pruning well. Evergreen and attractive all year. Small, oval, tooth-edged leaves. Fragrant tiny white flowers in spring. Here in Seattle it can take the full sun but partial shade is okay too.
Great Plant Picks is a local organization with information about plants that do particularly well in the Pacific Northwest.
1. Which plants can be rooted only with hormone?
2. Which plants cannot be rooted, even with hormone?
There is excellent general information on plant propagation in The Brooklyn Botanic Garden Gardener’s Desk Reference (Janet Marinelli, editor; Henry Holt, 1998), which explains which plants are most successfully propagated by seed, by division, by layering, by leaf or hardwood or softwood or stem cuttings, and by root cuttings.
There really is no resource that will provide a comprehensive list of plants that can or cannot successfully be propagated from root cuttings, but a member of the faculty here who specializes in propagation says that the key element that determines whether a plant can be propagated in that way is age. Each plant has different abilities, and some are easily rooted, such as Salix (willow), while others, like Quercus (oak), or Arbutus (madrona), are very hard to root, especially as they mature. As far as use of rooting hormone, it can help the process, and it will prevent rotting, but if you are a strictly organic gardener, you should be aware that it is a chemical substance.
To renovate old Buxus hedge, when is the best time to cut back to 15-30 cm shoots? It appears that new shoots are pushing through now. My American Horticulture Society Pruning and Training book suggests late spring, but that may not apply to Seattle.
I consulted a local organization, Plant Amnesty, and their information sheet on Buxus says that April is the best time to prune. It is important not to prune when it is either too cold (leaves will turn grey) or too hot (same result).
Peter McHoy’s book, A Practical Guide to Pruning, also says to do your renovation pruning in mid- to late spring, and further suggests that drastically reducing the height of the hedge should be done in stages, over two to three years.
What is the purpose of the chemical in store-brand rooting hormone? I’d rather not use anything with chemicals when I’m propagating plants. Are there alternatives?
The chemical in rooting hormone (usually Indole-3-Butyric acid) acts as a growth stimulator. In commercial rooting hormone formulations, it may be combined with fungicide to prevent the development of fungus/fungal diseases during the rooting process, as is the case with a common brand, Rootone, which contains Thiram (a fungicide). The Environmental Protection Agency has more information about Indole-3-Butyric acid.
If you would rather not use synthetic rooting hormone, you can skip this stage altogether, or you can try making willow water to encourage rooting instead. Oregon State University (now archived) explains how to make a rooting tonic using willow.
Why do willow trees propagate so easily?
The technical explanation is that willows (Salix) have preformed or latent root initials that will elongate into an established root system when a part of the parent plant is removed.
If you were to take cut willow branches and make a kind of tea by soaking them in water, that water could be used as a sort of natural rooting hormone to help root other types of plants. This indicates that willows naturally contain a high level of the hormone that contributes to root formation.
I am looking for information about seed germination of Lardizabala biternata. I am wondering what temperature is best for its germination, if it requires light or darkness to germinate, if it needs to be stratified before germination, and the number of days it takes to germinate. I have the seeds started in my greenhouse at 70 degrees under lights and nothing seems to be happening! I have searched the web and looked at all of my reference books, but do not seem to be able to find this information. The seeds came from Sheffield’s Seed Co., Inc. (www.sheffields.com). They do not have any information on their website, although on the seed packet it states that more research is needed!
Below is information on propagating Lardizabala ternata from Plants for a Future.
Propagation
Seed – sow spring in a greenhouse. Prick out the seedlings into individual pots when they are large enough to handle and grow them on in the greenhouse for at least their first winter. Plant out in early summer and, if possible, give the plants some protection for their first winter outdoors. Cuttings of half-ripe wood, 5-10cm long with a heel, June/July in a frame. The cuttings should be put in individual pots. A good percentage. Stem cuttings in spring and autumn.
After locating an article by Dan Hinkley (Washington Park Arboretum Bulletin, Winter 2004), I decided to widen the search to include information on germinating Akebia as well, since they are related.
The California Rare Fruit Growers site has Akebia germination information that might be useful.
The Royal Horticultural Society A-Z Encyclopedia of Garden Plants only says that Lardizabala seed should be sown in containers in a cold frame in spring.
We are looking for a good screening tree/shrub that is evergreen and interesting. The plant cannot grow over 6 feet high. We have very sandy soil, western exposure, and live in the Magnolia neighborhood. We would like it to be drought tolerant as well. I found Myrtus communis (Myrtle) and Rhus (Sumac)–I am not sure which variety of sumac would be best. I found the information on these plants in the Sunset Pacific Northwest Garden Book. I would love to get your advice on these, and if you have any other ideas as well.
Because of the height limitation of your site, I suggest primarily shrubs (rather than trees) that are evergreen and drought-tolerant.
Most of the Rhus I have seen growing in Seattle is of the deciduous type, but there are several evergreen varieties, such as Rhus virens and Rhus lancea. They are natives of Texas and Baja California. They will not be as hardy as the deciduous varieties.
Myrtus communis does well in seaside gardens although it can exceed your 6 foot height limit, reaching 10 feet or more (according to W. J. Bean, Trees and Shrubs Hardy in the British Isles, 8th ed., John Murray, 1973 and Top-Rated Evergreen Shrubs, Golden Press, 1983). The dwarf variety Myrtus communis ‘Compacta,’ would be too low-growing to act as a screen.
I would suggest Osmanthus delavayi, which has small, glossy dark green leaves, and very fragrant white flowers in March. It can eventually grow to 8 feet, but is easily maintained as a hedge or screen (see the website Great Plant Picks for pictures and information).
Other ideas would be Arbutus unedo ‘Compacta’ (Strawberry Tree). Or you could try Ceanothus concha, which has small dark green leaves and blue flowers. The California nursery Las Pilitas has information about this and other varieties of Ceanothus.
You may also wish to come to the Miller Library and browse the many illustrated books on shrubs and trees.
I have two different elderberries that I would like to prune.
1. The first is a ‘Sutherland Gold’ (a cultivar of Sambucus racemosa) that is 5 years old, and I have never pruned it.
2. The second is a ‘Black Beauty’ (a cultivar of Sambucus nigra) that I just bought last year.
When should I prune? At what point on the stems? How far from the ground?
I consulted Peter McHoy’s Practical Guide to Pruning, (Abbeville Press, 1993), and he recommends cutting one stem in three in mid-spring on plants that have been established for three or more years. You would cut to just above the ground level, choosing to prune out the oldest and weakest shoots first. Continue with cutting out shoots that will open up the center of the plant or improve its shape. It may look sparse afterwards, but new shoots will grow and fill in the space.
If you are growing the plants mainly for their foliage, he suggests cutting all the shoots back to 1-2 inches from the framework of the old wood in mid-spring.
Below is some more detailed information from the website of the Ontario Ministry for Agriculture, Food and Rural Affairs, which assumes you are growing the plants for their fruit production.
Pruning:
“During the first two seasons plants should be encouraged to grow vigorously with little to no pruning required. After the second year, pruning should be done annually in early spring. All dead, broken and weak canes should be removed. Three-year-old canes should be removed as they produce less fruit and appear to be more prone to winter injury. Removal of older canes will encourage the growth of new, more fruitful canes.
“Mowing of all the canes in a mature planting may be a method of reducing labour costs while encouraging growth of new canes. The disadvantage of this system is that there is a loss of production in the season following mowing as there is limited production on the one-year-old canes.”
Bulbs in pots – when to plant?
Daffodils & tulips wilting in pots now, what to do with them? Can you put them in the ground right now, or should you wait till fall? Keep them dry, wet, what?
Yes, you can put them in the ground right now or you can lift them, keep them dry and plant them in the fall. Growing in pots is stressful to bulbs, so you may find fewer flowers next year.
Most tulips do not flower reliably each year, even if they were grown in the ground, so many people treat them as annuals (dig up and toss!) BUT some tulips do re-flower (Darwin Hybrids, Fosterianas and species tulips) so if you are not sure what you have, go ahead and replant. Both tulips and daffodils dislike summer water, so make sure you either plant them in a place where they will stay dry or make sure they are planted in really well-drained soil. Mixing gravel into the soil can help with drainage.