December 2003
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Garden design using shade plants and shade trees   

Gardening Newsletter - December 2003, Issue 16

While I’m enjoying the mild weather we are having on the East coast, I worry about the plants. I saw a daffodil springing up from the ground yesterday. If this weather continues the plants will be extremely confused. Is it global warming or Mother Nature playing tricks?

The big news for the coming year at My Shade Garden is that a considerable effort is going to be made on adding more shade loving plants to the plant database. We are on a mission to disprove the notion that nothing grows in the shade.

We are already getting busy with requests for garden installations in the spring. Its not too early to start making your gardening plans. Order your garden designs now, before the busy season!

Happy Holidays!

Rebecca Green
Horticulturist

Salt: Fertilizer or Ice Melt

Fertilizer or SaltYou may have heard of fertilizer burn. Fertilizer burn occurs when a plant is exposed to an excessive amount of salt. The salt causes the plant to loose water and get brown spots. Yes, most non-organic fertilizers, chemical fertilizers, contain a large amount of salt. That is why you can sometimes kill a plant or your lawn if you fertilize it too much.

Of course salt is also used to melt ice in the winter. As such, if you need to melt some ice near a garden or lawn area an ideal method would be to use a chemical fertilizer. As the ice melts the water that runs off into your planting area will fertilize your plants. However, you shouldn’t overdo a good thing. Just like you can damage or kill your plants in the growing season from too much salt in fertilizer, so can you in the winter.

There are many different types of salt. Urea, which is common in chemical fertilizers, only melts ice when the temperature is 21 degrees F or warmer. Sometimes fertilizers contain calcium chloride or magnesium chloride. These salts melt ice until the temperature drops down to –25 degrees F. Sodium chloride, which is table salt, melts ice down to 12 degrees F. Of all of these salts urea poses the least threat to plants.

Frequently, plants along highways are severely damaged or killed from road salt. Some plants are more sensitive to salt than others. Consequently, when planting a screen or hedge to block the view of a road care should be taken to select salt resistant plants.

The following trees are somewhat resistant to salt:  

Leyland cypress

X Cupressocyparis leylandii

Russian olive

Eleagnus angustifolia

White ash

Fraxinus americana

Black ash

Fraxinus nigra

Honeylocust

Gleditsia triacanthos

Kentucky coffetree

Gymnacladus dioicus

American holly

Ilex opaca

Southern magnolia

Magnolia grandiflora

Sweetbay magnolia

Magnolia virginiana

Live oak

Quercus virginiana

Japances pagodatree

Sophora japonica

Black pine

Pinus nigra

 Of these plants, Leyland cypress (X Cupressocyparis leylandii) makes the best screen. However, American holly (Ilex opaca) is the most shade tolerant.

Many pines are sensitive to salt damage, especially white pine (Pinus strobes). Unfortunately, I see this plant frequently used along roads. If you want to use a pine to block the view of a road black pine, Pinus nigra, is the best.

Saxifraga: Shade Loving Succulents

One of the things I love most about horticulture is that there are so many plants you never run out of things to learn. During my studies at the New York Botanical Garden (NYBG) I had to “learn” about many hundreds of different plants. However, my contention has always been you really don’t “know” a plant until you live with it and try to grow it. As such, every gardening season I try to acquire several of the more unusual plants I “learned” about at NYBG in attempts of really getting to “know” them.

A genus of plants that I am currently very excited about getting to “know” up close and personal are Saxifraga, commonly called saxifrage or rockfoil. The name Saxifraga is an old Latin name used by Pliny. It comes from two words saxum, meaning rock, and frangor, meaning to break. It was believe that the plant could break stones in the bladder.

Saxifraga is a genus of about 440 species of mostly succulent, evergreen, mat forming perennials. A few are semi-evergreen and a handful are biennials or annuals. They frequently produce star-shaped or shallowly cup-shaped flowers in shades of pink, white, and yellow. Some of the cup-shaped flowers are known to catch rain and dew. They are mostly native to the North and South Temperate and Arctic regions. A few are found in Asia. They are rare in South America and absent in Australia, South Africa, and the Pacific islands. Some grow in woodlands, while others grow on open hillsides sloping toward the west or northwest rather than the south.

Saxifraga are member of the plant family Saxifragaceae, which includes many well-known shade-loving plants. Foamflower, botanically called Tiarella, is also a member of this family. Heuchera, also known as coralbells, is a member of the Saxifragaceae family too. The family also includes shrubs, such as: Philadelphus (mock orange), Deutzia, and Hydrangea.

With about 440 to choose from, Saxifraga vary considerably, making it difficult to describe your average Saxifraga. However, the appearance of many reminds me of Sedum (stonecrop) or Sempervivum (hens and chicks). There are two major differences for gardeners between Saxifraga and these other succulents: (1) many (not all) Saxifraga love shade, even deep shade; (2) they also like alkaline soil.

Botanists have categorized Saxifraga into sections based on their physical characteristics. Most literature on Saxifraga refers to these sections as though everyone who has passed second grade obviously understands what is being discussed. Of course each section has a difficult Latin name. Don’t be intimidated. Provided below is a short description of the characteristics the plants in each section has. Use this to help you figure out what section(s) of plants will best suit your conditions, needs, wants, and desires.

Section Gymnopera (Robertsonia)

Saxifrages with evergreen, rosetted leaves, flowers in panicles (bunches) on leafless flower stems. Includes the popular variety London pride. Loves shade.

Section Irregulares (Diptera)

Mostly used in rock gardens. They are natives to woodlands, so they like shade. The leaves are usually deciduous. They flower in summer and fall.

Section Ligulatae (Euaizoonia)

These Saxifraga grow best between rocks and are known as the silver Saxafraga. Their silver leaves grow in rosettes and they have sprays of white, yellow, or pink flowers.

Section Porphyrion (Porophyllum)

These Saxifrages bloom in January and February. The leaves are usually evergreen and encrusted in lime from the alkaline soil they grow in. Botanists have subdivided this group into three categories: Eugleria, Kabschia, Oppositifoliae.

The Kabschia Saxifraga are best planted in a scree garden. Scree is a term used to define soil that is composed of loam, sand, leaf mold, and lots of crushed stone. The plants should be planted on a slope facing north or northwest. Good drainage is essential. The roots love to grow under and around large rocks.

Section Saxifraga (Dactyloides)

This group includes what are commonly called the mossy saxifrages. They need a cool, partially shaded spot and spread quickly. After they flower put a fine mixture of sifted loam, leaf mold, and sand on top of them. Gently work the mixture between the leaves with your fingers. A good overhead watering will also help settle the mixture.

This group of Saxifraga tends to turn brown and patchy with age. Eventually it is necessary to dig the plants up, enrich the ground with leaf mold, and divide and replant the plants. This may be done in either spring or fall.

Full sun causes the flowers, especially the red ones, to fade.

Section Xanthizoon

These plants grow into mats or cushions of evergreen fleshy leaves. They get yellow or orange flowers.

Most Saxifraga have similar growing requirements. They all need shade from the midday sun, good drainage, and high humidity when the temperatures are hot. The soil should be gritty, not too rich or poor in nutrients. They enjoy wet springs, but can withstand dry summers. Many require alkaline soil. If your soil is acidic you can make it alkaline by adding lime.

The biggest difference between the growing requirements of the various Saxifraga is the amount of shade a particular species needs. None of them like hot midday sun. However, some need more shade than others. Those whose native habitat is woodland need the most shade. Those that are from mountainous regions prefer to be planted on a north or northwest exposure with protection from the hot sun. Provided below is a description of some that like deep to partial shade.

Saxifraga cortusifolia

This plant is in section Irregulares. Its leaves are kidney-shaped to rounded, lobed, and a glossy green. In late summer it produces small panicles of white cup-shaped flowers. A panicle is a botanical word for a bunch of flowers, resembling a tiny bunch of grapes, only they are bunches of flowers. Plants grow to be about 6 inches tall and 8 inches across. They are native to Japan and hardy in Zones 5-7.

There is a variety of this plant that is sometimes called Saxifraga fortunei. Its full name is Saxifraga cortusifolia var. fortunei. It gets a little larger than the straight species described above, about 1 foot tall and wide. It also needs warmer weather, being hardy in zones 6-8.

The cultivar ‘Rubrifolia’, full name Saxifraga cortusifolia ‘Rubrifolia’, has a lot of red in its leaves. It gets about 8 inches tall and wide.

Saxifraga cuneifolia

These Saxifraga are in section Gymnopera. They have wedge-shaped, green leaves that are purple on their under side. They produce loose panicles (bunches) of white star-shaped flowers that are spotted yellow, or sometimes red. They grow to be about 8 inches tall and 12 inches wide. They are native to Europe (Carpathians to Pyrenees). This plant is hardy in zones 5-7.

Saxifraga x geum

This plant is the child produced by crossing Saxafraga hirsute and Saxafraga umbrosa. It is in the section Gymnopera. It is mat-forming and produces panicles (bunches) of white star-shaped flowers. Its stems are hairy. It grows about 8 inches tall and wide. It is native to Pyrenees and hardy in zones 6-8.

Saxifraga x primulaize

This plant is the result of crossing two other types of Saxifraga. One parent is Saxafraga aizoides and the other is Saxafraga x urbium or Saxafraga umbrosa. This plant is sometimes called Saxafraga ‘Primulaize’. It has fleshy, oval leaves that are green. In summer it gets panicles of star-shaped crimson- or salmon- colored flowers. It is short, only growing about 3 inches tall and 6 inches wide. It is hardy in zones 6-7.

Saxifraga stolonifera, commonly called Mother of thousands

This Saxifraga is in the group Irregulares. It has kidney-shaped to rounded leaves that are deeply cut and green. In summer it produces panicles of white flowers up to 1 inch across, spotted with red or yellow. The flowers have 3 or 4 upper petals and 1 or 2 longer lower petals. It grows about 1 foot tall and wide. It is hardy in zones 6-9. The cultivar ‘Tricolor’, also called ‘Magic Carpet’, has leaves that are patterned red, white, and green. This cultivar is hardy in zones 7-10.

Saxifraga umbrosa var. primuloides also called Saxifraga primuloides

This plant is in the group Gymnopera. It has oval to spoon shaped, crinkled leaves that are green above and red below. It has loose panicles of red-spotted white flowers in summer. It gets about 12 inches tall and wide. It is hardy in zones 1-5. The cultivar ‘Clarence Elliott’, also called ‘Elliott’s Variety’ gets rose-pink flowers and grows about 6 inches tall and across.

Saxifraga x urbium commonly called London Pride

This popular hybrid is a Gymnopera, which means it is a quick spreader. It is a good ground cover, even in poor soil. It has large rosettes of spoon-shaped green leaves. In summer it gets panicles of pink tinted white star-shaped flowers. It grows about 12 inches tall and its spread is indefinite. It is hardy in zones 6-7.

Saxifraga can be used many ways in the landscape. They are excellent planted in walls and rock out croppings. They are ideal in rock gardens. Those that spread make attractive ground covers. They can be used in planters too. Some thrive on moist soil and would be great on a stream bank or around a pond. If you have a lot of succulents in a sunny portion of your garden and want to continue the theme into the shady areas of garden, Saxifraga are the solution. They are also attractive planted around and beneath trees and shrubs.

If you would like to learn more about Saxifraga the Saxifrage Society is a great source. Their website can be found at http://www.saxifraga.org.

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