iGrow Gardening: Elm tree propagation

David Graper
SDSU Extension Horticulture Specialist

Q I want to start some cuttings from an American elm. Got any pointers? Timing to make the cuttings? Do I need to constantly mist the cuttings or just the soil? Temp – air and soil? Any and all info is greatly appreciated.

A Traditionally, most American elms were just propagated by seed. But as new cultivars were selected, vegetative propagation methods had to be utilized in order to maintain the characteristics of these desirable cultivars. Vegetative methods to produce clones of these desirable cultivars included budding, plant tissue culture and of course cuttings. Since the devastation that Dutch elm disease caused, nearly wiping out the American elm population across the U.S. several new cultivars have been developed that are resistant to this disease. These must be propagated vegetatively to maintain that resistance. Keep in mind that these new disease resistant cultivars, as well as most named cultivars, are typically only propagated by licensed propagators that pay a royalty to the originator.

I checked online and found a few recent studies that described some propagation protocols. It seems that the best option was to use softwood cuttings, harvested in the spring when the new shoots are about 3 inches long. Use a clean, new razor blade to remove the shoots from the tree, then immediately wrap them in moist paper towel and place them in a plastic bag to prevent them from drying out. It is best to harvest the cuttings early in the day when it is still cool, and the cuttings are fully turgid.

The cuttings will need to be dipped in rooting hormone, which contains a mixture of auxin usually IBA or IAA. Small containers or packets of rooting powder or sometimes a liquid formulation can usually be found in the gardening department of hardware stores, discount outlet stores or local garden centers. You will also need a rooting media and container to hold the media. Homeowners should be able to find root cubes, flats to hold them and a clear plastic dome to cover the flat and to maintain high humidity inside the flat. One article suggested using Grodan ‘A-OK’ 1.5 in Starter Rootplugs which are made out of rockwool. But I would think that some of the peat-based or Oasis plugs would also work. Start with a brand new flat and plugs to avoid any chance of contamination from previous use. Or, an older flat could be used if disinfected with 10 percent bleach and then thoroughly rinsed with distilled water several times. Use new plugs. Saturate the plugs with clear water. Remove the lowest leaves of each cutting so that there is about 1 inch of stem exposed. Recut the stem end at a 45-degree angle with a new razor blade then dip the 1-inch end into the rooting powder or liquid. Shake off the excess, then insert the cutting end into the root cube. If necessary, use a small dowel to make a hole first, to accommodate the cutting. When you have all of your cuttings inserted, use a clean spray bottle filled with distilled water to thoroughly mist the cuttings as well as the inside of the flat and dome. Place the dome over the flat then move the whole flat and dome to a bright location to allow the cuttings to root. Some sun exposure is good, but you do not want full sun exposure all day or it may get too warm inside the flat. Alternatively, the flat could be placed under fluorescent or LED lights about 12 inches below the lamps. Monitor the flat to make sure that it does not dry out. There should always be evidence of some condensation on the plastic dome. If necessary, remove the dome and mist with more distilled water.

Check the cuttings after three weeks to see if any have begun to form roots. Grasp a leaf and give a small upward tug on the cutting. If there is resistance, it has likely formed roots. If the cutting just comes out, it may need more time to root. If it has wilted it will likely not root.

In a commercial setting, cuttings may also be rooted in perlite under intermittent mist, with the mist on for 15 seconds every 5 minutes or so. Do not expect all the cuttings to root. Elm cuttings can be difficult to root, often with only 20 to 40 percent success. Once roots grow to an inch in length or so, the plugs can be potted up into potting media. Gradually decrease humidity so that the new little trees have time to adjust to normal humidity levels. Obviously, it is going to take quite some time for these little plants to grow large enough to eventually transplant outdoors and then become acclimatized to outdoor conditions. They will need protection from animals like rabbits or deer that might eat them too. They will need to be given a cold treatment over the winter to allow them to go dormant and set buds for next year’s growth too. It may take a few years before they can be finally trans planted to their permanent location.

The National Garden Bureau Declares: 2019 – Year of the Salvia nemerosa

From tropical forests to high-deserts and urban landscapes, Salvias are among the most common ornamental and culinary plant species you will find.

Although its name is derived from the Latin salvere, meaning to heal or good health, this moniker undoubtedly refers to the common herb Sage (Salvia officinalis) and not the ornamental Salvias we find flowering in our gardens. All Salvia are in the mint family Lamiacea and are cousins to landscape favorites such as Nepeta (Catmint) and Monarda (Beebalm). Indeed, many Salvia species reveal their history through their minty fragrance contained in their leaves. There are more than one thousand species in the genus; however, most are not hardy in northern gardens. This article focuses on the hardy types.

Hardy Salvia History

English botanist George Bentham did the first extensive documentation of this genus in 1836. One fascinating characteristic of Salvia flowers is that they contain a trigger mechanism that deposits pollen on the back side of visiting bees. This pollen then becomes transferred to female Salvia flowers that share the same receptive flower parts encouraging pollination among the same or similar species. The beautiful Salvia we find in our modern gardens originates from plants found in the wooded elevations of Eurasia. The most common hardy species are S. nemorosa and S. pratensis and the many hybrids derived such as S. x sylvestris and S. x superbum. Today, we typically refer to the entire class of these hybrids as S. nemorosa (nemorosa from the Latin ‘of woods’) for simplicity and the reason why we commonly refer to these hardy plants as Woodland Sage. Interestingly, all plants with the common name of Sage are Salvia, but we reserve the true genus name for ornamental rather than culinary species. The Sage you keep in your kitchen is actually Salvia too, and it can also be winter hardy in the north; however, they have lesser ornamental value.

Key Cultivars

Much of the early work in hardy salvia breeding was done by German plantsman Ernst Pagels who is credited with breeding varieties ‘Blauhugel’ (Blue Hill) and ‘Schneehugel’ (Snow Hill) shortly after the Second World War. Both of these are still in commercial cultivation and are found in garden centers during spring and summer.

Today, there are several hundred varieties of hardy garden Salvia from which to choose. Likely the most common and well-known cultivar, also a product of innovative German breeding is ‘Mainacht’ (MayNight). Named Perennial Plant of the Year by the Perennial Plant Association in 1997, May Night remains a favorite among landscapers for its abundance of indigo blue flowers and pest and disease resistance. Other standards include the upright, dark-stemmed variety ‘Caradonna’ and the dark purple cultivar ‘Ostfriesland’ (East Friesland). These tried-and-true classics are being replaced slowly with exciting new varieties from flower breeders in the United States and Europe. Award-winning cultivars such as ‘Blue Marvel’ and ‘Rose Marvel’ present extra-large flowers and provide a much longer flowering window. Newcomer ‘April Night’ is earlier to flower, as the name suggests, and is especially popular with southern gardeners. ‘New Dimension’, ‘Bordeau’ ‘Salute’ and ‘Swifty’ are all new introductions that are bred for improved garden performance. Of interest to the category, breeders are hybridizing S. nemorosa and S. pratensis to provide plants with more open and airier flower presentation. Examples include the Fashionista series and Salvia ‘Blue by You’.

Care and Cultivation

Hardy Salvia like S. nemorosa are considered to be care-free and easy to manage in the garden. They can be in place for years without a need for dividing. They are also a favorite of pollinators like bees and hummingbirds. As a member of the Mint family, their leaves are not on the preferred forage list of deer and rabbits and considered to be a great garden addition where these creatures are a nuisance. Be sure to plant in a location where they will receive at least one-half day of direct sunlight, as this will provide an environment that encourages the highest degree of flowering. Salvia prefers soils rich in organic matter, so it may be necessary to add compost, peat moss or topsoil to your sandy or heavy clay soil before planting. Once established in the garden, Salvia is quite drought tolerant and require watering only when other landscape shrubs such as Hydrangea show signs of wilting. To maintain healthy green growth, plan on fertilizing your Salvia plants when they emerge from dormancy in the spring and once again in early summer. Applying a balanced fertilizer such as 15-15-15 according to label directions will do the trick. Many gardeners experience only one spring flowering display from Salvia because they are unaware that these garden beauties can be encouraged to rebloom several times during the summer and well into fall. Once the first flush of flowers has finished and the flower stems have turned brown, cut the plants back aggressively to about one-third their original size. Doing this causes the Salvia plants to push up new shoots from the root system, and you will be rewarded with a new flush of flowers in four to six weeks. Repeat this process, and it’s possible you may see as many as three or more full cycles of flowering in a single season. Remove all Salvia foliage after it turns brown in the fall to promote healthy new growth the following spring.

Hardy garden Salvia are delightful additions to any central and northern garden, and it is fitting that the National Garden Bureau has deemed 2019 as the Year of the Salvia!

Intermittent mist popagation bed.
Peat pellets also work well for cutting propagation or starting seeds.
Salvia Blue Bouquetta.
Salvia Burgundy Candles.
Salvia Caramia.
Salvia New Dimension Blue.