Alpine Container Gardening

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Listing
of Alpine Plants and how to use
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There is a rich tradition of European and
American alpine and rock gardening using containers, raised beds, alpine
houses, and open gardens. “Trough” gardening, or the use of stone troughs for
miniature gardens, is the most popular, yet only one of several alpine
gardening forms. This article explores growing alpine plants in containers in
general.

Alpine container gardening incorporates many
styles and forms, as specimens or collections, miniature gardens, living art,
bonsai-like creations, and even tiny, picturesque landscapes. As single
specimens or in groupings, containers accentuate the beauty of certain species
in their unusual forms and rich blooms. Combinations of alpines can create
finely-detailed, miniature gardens or artistic collages with striking contrasts
in color, texture, foliage, and shape. As focal points or as part of a
miniature landscape, dwarf trees and shrubs can add further detail and contrast
with the other elements.

What are alpine and rock garden
plants?

Alpines refer to plants that grow above the tree-line,
generally from higher elevations. Alpines are exposed to various conditions
including extreme moisture levels, low nutrient levels, wide temperature
ranges, shifting substrates, grazing by animals, exposure to wind, and high
light levels. Adaptations include small size, shapes that minimize exposure to
the harsh wind and cold, dormancy under snow, mineral encrustation and crystal
growths, foliage coloration, extensive roots to cling to mountain sides or seek
water and nutrients, hairs for condensation, or spiny growths to deter grazing.
It is important to note that there are many permutations of alpine and
subalpine climates. Alpines thrive in specific conditions, but often can not
compete or survive under certain lowland or even differing alpine
conditions.

Rock garden plants, which include alpine plants, generally
refer to any plants suitable for rock gardens, based on size, foliage,
compatibility with other plants, appearance, growth rate, and other factors.
The categories of rock garden and alpine are interchanged fairly freely.

Which plants are good for containers?

Hundreds of fascinating alpine and rock garden plants are
suitable for container gardening. Depending on the desired effect, plants come
in various forms including mats, cushions, and mounds. Grey, “silver”, and
green mat plants include the raoulia, arenaria, saponaria and azorella. Popular
“cushion” plants or dense, hard mounds include scleranthus, silene, armeria,
and alpine dianthus. There are moss-like “green rocks” of androsace and draba,
as well as alpines that feel like rocks in the calcium-encrusted saxifraga.
Alpines also include the needle-sharp pincushions of the acantholimon,
dianthus, and arenaria. Suitable rock garden plants include numerous heathers,
small shrubs, woodland plants, dwarf or miniature conifers, and small bulb
plants.

Given the wide range of alpine and rock garden plants, there
are practical and aesthetic considerations to guide your selection. Practical
factors include suitability for your climate, size at maturity, nutrient needs,
moisture requirements, and light requirements. The bottom line is the plants
need to thrive and survive in your climate and particular conditions. Aesthetic
factors include color, bloom, texture, comparative size, shape, and foliage.
Books, alpine society journals, and the Internet are good places to find
descriptions and specific needs. What you choose should be based on your
particular tastes and the combined effect you have in mind.

Where can you find alpine plants?

Many local nurseries carry rock garden plants, but usually a
limited number of alpines. Some botanical gardens and arboretums, such as
Strybing Arboretum Society in San Francisco, propagate a number of alpine
plants for regular fund raising sales. A few specialist nurseries throughout
the country also carry alpines. A wide range of plants can be obtained through
mail order companies. Seeds can be obtained through mail order and in
alpine/rock gardening society seed-exchanges.

Plants should be purchased carefully to match your planting
scheme. Plants may be incorrectly identified as rock garden or alpine plants
and can include overly invasive plants or plants that will grow too large.
Also, one should be careful with alpines planted in regular soil and with too
much fertilization. Many of these plants thrive in the rich soil in summer, but
will die from the same conditions in fall and winter if there is too much
moisture. If you do like a particular plant, you may try to remove the soil
from the roots and transplant into a more suitable medium.

It helps to see or read descriptions about the actual
species in gardens, magazines, or books. Many plant genera have a number of
species, both alpine and non-alpine, that vary greatly in form. For instance, a
Gypsophila aretoides is a dense, flat, green mat, while Gypsophila paniculata
is the Baby’s Breath commonly used in flower arrangements. Similarly,
while most gardeners associate Dianthus with carnations and border pinks,
alpine Dianthus are appreciated more as tight mounds or domes with various
foliage color and texture.

What conditions do alpine plants need?

With numerous exceptions, alpine plants generally need
excellent drainage, bright light, protection from winter moisture, and low
nutrients. Many alpine plants are adapted to dry or fast-draining conditions
with fresh water. Consequently, the plants may be susceptible to root rot when
exposed to overly wet conditions such as standing, stagnant water. With some
exceptions, alpines grow in high light due to direct sun exposure and lack of
competition from other plants. Many alpines become dormant to survive winter.
Some are protected under snow cover that keeps the plants relatively dry.
Consequently, many will die if exposed to excessive moisture while dormant.
Lastly, most alpines grow in low nutrient substrates. Excessive nutrients or
organic matter may cause irregular plant growth.

Certain plants require alpine houses or cool green houses to
survive the fall and winter. It is helpful to talk with experienced growers to
find out what plants do best in your area. You can also observe which alpines
thrive in local botanical gardens.

What containers are suitable for alpine
plants?

Alpine container gardening has several advantages. Alpine
containers allow elegant gardening in unusual settings including patios, decks,
balconies, sidewalks, and rooftops. Elevated containers allow a closer view of
the plants. Planting mix and location can be controlled to match the
plants’ needs. The appearance improves with each growing season as plants
fill in and form mounds. Given advantages to using containers, there are both
practical and aesthetic factors in selecting a container.

Practical factors for container selection involve drainage,
depth, volume, weight, and durability. For drainage, containers need holes in
the bottom to allow excess water to drain away. Saucers should be avoided,
where containers sit in water. Container depth is vital where plants will be
exposed to significant rainfall, particularly in the fall and winter. Deeper
pots create better drainage, promote root growth, and allow for greater
low-capacity water retention. While alpines can run roots deep in search of
water, many will suffer if they are only few inches from standing water at the
bottom of a pot. Greater volume allows more room for root development. However,
increased volume means more weight when it comes to moving pots around or
placement on a weak structure. Durability is another factor as alpines can live
in containers for years. Stone, clay, plastic, and solid hypertufa containers
may last for decades, while wooden boxes, wine barrels, and the popular
hypertufa-coated styrofoam container can deteriorate over time.

Aesthetic factors of containers depend on your personal
tastes. These include the size, color, patterns, style, shape, and texture of
the container, as well as the scale compared to the plants. The characteristics
should match the your planting as well as its surroundings.

Can you make your own trough or
container?

Troughs can be great containers for alpines, given
sufficient depth and volume. Troughs come in various sizes and forms, and offer
different options for garden structure and formality. For those who want the
classic look of stone trough planting, but can not find or afford a trough,
there are many people who create their own. You can cast a hypertufa trough or
coat a styrofoam container or a sink with hypertufa mix to create the
appearance of a stone trough. While this article focuses on the planting of
containers, rather than trough building, one recipe for hypertufa is a mix of
one part portland cement, two parts perlite, pumice, or course sand, and two
parts of peat moss. There are many articles and books that can provide
additional recipes and detailed instructions on building your own trough.

What kind of potting mix should be
used?

There is a range of potting mixes suitable for alpines. For
mixed plantings, mediums must be developed to suit the needs of various plants.
As a general rule, the planting mediums must have high drainage, good aeration
for the roots, and adequate nutrients. Most mediums are a mix of inorganic and
organic materials.

Inorganic or drainage materials provide the base for the
mix. Many growers use from 50% to 90% inorganic materials, including gravel
(1/4″ or less), pumice, very coarse sand, perlite, and other materials. Some
reputable growers use 100% inorganic materials. Fine sand (builders and beach
sand) and vermiculite are generally not recommended for containers as they do
not contribute to aeration. Many of these ingredients are available at
nurseries, and landscape and building suppliers. While there is a wide range of
recommended mixes, I tend to use very lean mixes and rely on very dilute
fertilization for nutrients.

Inorganic amendments can be added to provide mineral
elements. Small amounts of green sand (glauconite), rock phosphate (not super
phosphate), red lava rock, and stone meal can provide nutrients over time. Red
lava rock should be used sparingly as it can melt into a clay-like material
under wet conditions. Some nurseries use slow release fertilizers to increase
growth for sale, but these should be used in moderation.

For organic materials, many growers use various soil-less
ingredients such as peat moss, leaf mold, compost, bark, and commercial
soil-less potting mixes. I use combinations that last in the medium and will
not impair drainage. Garden soil is not recommended for alpines in containers
due to the potential for weeds and other problems. Regarding the core
ingredients, you can combine materials in different ways as long as a suitable
balance is maintained between inorganic and organic materials.

Certain plants will require or grow better with specific or
greater proportions of organic material. Based on plant needs and growing
conditions, there is a delicate balance between the amounts of organic material
and drainage materials. Often plants with a good organic base and poor drainage
may thrive in the summer, only to die in winter due to excess moisture. As a
general rule, the drier your winter, the more organic materials you can use.

How do you set up the container?

Set up includes creating the potting mix, preparing,
planting the alpines, hardening off, placing the container, and care until
plants are established.

Create the potting mix using the guidelines in the section
on potting mixes. You can use a wide screen to cover the drainage holes to keep
in the materials. Fill the pot partially to the level at which you will place
the plants. One suggestion is to have a leaner gradation of the planting medium
toward the bottom of the pot. Tamp the mix down lightly and avoid creating air
pockets.

Plants may require minor preparation while planting.
Carefully pick out any weeds, moss, or liverwort around the plant. For plants
that are root bound in their growing pots, it is often necessary to tease out
the roots to ensure new root growth. If the plants are from mail order, it may
be necessary to gently loosen the root ball before planting. Some growers
suggest bare-rooting the plants to encourage plants to extend roots in to the
potting medium, although care should be exercised to minimize root damage.
Examine the root system and original planting medium to determine the
conditions under which the plant was raised. You may be able to determine the
level of watering as well as the richness of the medium. If plants were grown
in regular soil, remove as much soil as you can without seriously damaging the
root system.

Plant the alpines at the soil level in which they were
grown. A layer of top dressing, such as gravel or pumice, or thin sheets of
rock may be used to lift the plant from direct contact with the planting mix.
Mound the material so the plants and soil level is just above the container
rim. This will promote the mounding effect and will compensate for some
settling of material over time.

The plants may need to be hardened off before and/or after
the planting by leaving plants outside in partial shade. If the plants were
raised in a colder climate, plants may need to acclimate to the new light and
temperature range. If the plants have limited root growth such as young
cuttings or suffer root damage in the transition, the roots need to be
established before exposure to strong sunlight. For example, many dwarf
conifers can tolerate strong sun, but only with an extensive root system.

Place the container in a location that meets the needs of
the plants. Most alpines and rock garden plants prefer a sunny or well-lit
location, although there are some that do well or better in partial shade or
full shade. If heavy, containers should be planted at or close to its selected
site. Containers with alpines can be quite heavy due the planting depth
required, the container used, and the type of growing medium. Care should be
exercised in moving the pots, both to protect the container and your back. Due
to light and air circulation requirements, alpines should be grown outside or
in alpine houses. Cool, well-ventilated, green houses or alpine houses are
ideal for alpines that can’t survive winter wet or excessive rain.

Provide care for plants after the planting. Alpines may need
sun protection and increased watering for a short period after planting until
the roots extend into the container. Pick out any weeds that surface. As the
medium settles, add extra top dressing if roots become exposed.

Care and Maintenance

Once set up, alpine containers are relatively low
maintenance. Regular care includes watering, fertilizing, weeding, controlling
aggressive or out-of-scale plants, protection from pests, and winter
protection.

Watering should be regular, but not excessive. Generally,
the growing medium should be damp, but not soggy. With established roots, many
alpines can grow in fairly dry conditions, although some alpines thrive with
frequent watering in the growing season. Given the lean potting mixture, the
plant should not be allowed to dry out completely. During winter dormancy,
plants should not be watered from overhead and should be kept relatively dry.

Remove aggressive or oversized plants that don’t match
the scale of the design. There are also a number of weeds, including tiny
alpine weeds, which thrive in rock garden conditions. Remove weeds carefully so
as not to damage the roots of desirable plants. Mosses and liverworts should
also be removed as these compete with alpines.

Light fertilizing is advisable during the growing season
given the lean planting mix. Nutrient needs vary according to the plant and
time of year, but a general rule is to dilute the fertilizer to quarter-normal
strength or less. With the right potting mix, fertilizing may not even be
necessary for some plants. Keep in minds that growth is slow and many
containers only fill out after a complete growing season. Even if the planting
appears sparse, resist the temptation to over-fertilize as you may create
abnormal growth that can die in winter.

Certain pests can harm alpines. Like other plants, some
alpines are susceptible to aphids, slugs, and snails. These can be removed or
prevented by picking them out, through the careful use of sprays and pellets,
or through organic means. Earthworms are generally discouraged in containers as
they may deposit too much organic material around the roots. Birds can also be
problematic as they occasionally pick apart cushions, pull out seedlings, and
stash their own seeds in the container. Barriers such as covers or stakes can
be used to discourage birds.

Winter is often the test for alpine survival. Winter
protection is required for certain plants that are normally dormant under snow
cover or live in otherwise dry winter climates. It may be necessary to move the
container into a green house or alpine house, or to provide direct protection
under a pane of glass or similar cover. For sensitive plants, watering should
be conducted from the side or bottom, rather than overhead. An antifungal/mold
treatment may be necessary if mold appears. For beginning alpine gardeners, it
is probably easier to start with alpines known to survive outdoors without
protection in winters in your area. Winter also shifts sunlight patterns and
may place plants that need light into shade.

Miniature Garden Design

Aesthetic factors have been mentioned throughout this
article. Alpine and rock gardening allows a wide range of options to suit your
tastes. While not restricting your own creativity and preferences, here are six
general recommendations.

First, combine and space plants with their ultimate size in
mind. Avoid plants that will outgrow the container or grow out of scale with
the other plants. If plants grow too large, they can be removed. Slower growing
plants may need a head start or extra space to develop away from more
aggressive plants. You can use more vigorous plants to compete with each other
and also start with larger specimens of slower plants.

Second, take advantage of contrasts in color, foliage, and
texture. Alpines come in a range of colors, with various shades of greens,
grays, “silvers”, and browns. The fine leaves can create fine detail. In
texture, many alpines are surprisingly dense and rough to the touch.

Third, consider a formulaic approach including using one or
more dwarf conifers, one or more mounding plants, and one or more matting
plants. This high/medium/low combination can create interest with contrasts in
height and color as well as create the appearance of a miniature garden or
landscape.

Fourth, move plants around to suit your design. Many plants
can tolerate the occasional move during the growing season if you minimize root
disturbance, particular in leaner mixtures. Your first planting attempts may
not create the effect you have in mind. As you learn more about the plants, you
will develop a sense of how the plants will grow and combine.

Fifth, patience helps greatly in rock gardening. Many of the
plants grow slowly and take one or two growing seasons to spread or fill out.
Some plants may need to have an established root system to really flourish.

Lastly, draw techniques and ideas from other gardening areas
such as bonsai, stonework, moss gardening, and Japanese and other forms of
Asian rock gardening. Plants, particularly dwarf conifers, can be shaped for
various effects. You can use effective positioning of plants and features to
create a sense of tension, motion, balance, or impact.

Word of encouragement and where to find more
information

Alpine container gardening is well worth exploring. There is
a wonderful array of plants virtually unknown in the regular nursery trade. You
can create tiny gardens for small spaces or projects on a grand scale. You may
enjoy learning which plants thrive under your particular conditions or what
mixes best suit your climate.

You can also get a head start by doing a little research.
There are many good books and journals on alpine gardening. The library can
give you a good introduction to the various forms of alpine gardening and the
range of alpine plants available. Look for books on alpine gardening, alpine
plants, and specific plant genera as well as the North American Rock Garden Society (NARGS) and
Alpine Garden Society
(AGS) quarterly journals.

The North American Rock Garden Society (NARGS) is another
good source. There are local chapters throughout the country. Many members have
substantial experience in growing and propagating alpine plants.

The Internet has many sources on alpine and trough
gardening, including instructional web sites with pictures and articles. There
is also the Alpine-L, an
on-line alpine garden journal, where numerous enthusiasts share
information.

Rick Lupp, Proprietor [253 847-9827]


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