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Rock Garden Basics

By Todd Boland (Todd_BolandMarch 31, 2012
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Are you trying to garden on a slope? Do you live in a wind-swept area where gardening is a challenge? Do you live on a mountain side or in a cold climate? Do you like to grow as many plants packed into one area as possible? Well rock gardening may be the solution! This article describes the basics in rock garden construction and the best plants to grow.

Gardening picture

(Editor's Note: This article was originally published on March 2, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.) 

What is a Rock Garden?

Basically, it is an attempt to recreate an alpine environment and to grow plants which are associated with an alpine (mountain) or similar area.  In the wild, alpine plants usually grow in mountainous areas above the tree line but they may also occur at sea-level in very exposed northern locations.  Not all rock garden plants are actually true alpines, but due to their small structure they are very suitable for a rock garden.

It should be noted that all low stature plants are not necessarily good choices for a rock garden.  Some plants are simply too robust or invasive as is the case with the popular snow-in-summer, Cerastium tomentosum.  Typical alpine plants are generally slow growing and non-invasive.  When deciding which plants to grow, it pays to get some information about the plant.  Such knowledge will prevent future disappointments.

Choice of Rock Garden Plants

The choice of rock garden plant is endless. Many are easy to grow while others are very challenging. The following list notes those which are relatively care-free and widely available.

Recommended Rock Garden Plants

Rock Garden Plant

Blooming Season

Flower Colour

Alyssum saxitile ‘Basket of Gold'

spring

yellow

Antennaria spp. - Pussytoes

early summer

whitish or pinkish

Arabis spp. - Rockcress

spring

white or pink

Armeria maritima - Thrift

early summer

pink or white

Artemisia schmidtiana ‘Silver Mound'

all season (foliage)

silver foliage

Aquilegia flabellata. - Dwarf Columbine

late spring

mostly blue

Aster alpinus - Alpine Aster

early summer

blue, purple, pink or white

Aster dumosus - Dwarf Michaelmas Daisy

early fall

pink, red, purple or lavender-blue

Aubretia deltoidea - Rockcress

spring/early summer

purple, magenta or lavender-blue

Campanula spp. - Dwarf Harebells

mid-summer

blue or white

Daphne cneorum - Rose Daphne

late spring

pink

Dianthus spp.- Pinks

mid-summer

combinations of pink and white

Euphorbia myrsinites - Spurge

late spring- early summer

yellow

Genista pilosa "Vancouver Gold"

late spring/early summer

yellow

Gentiana acaulis - Trumpet Gentian

late spring

deep blue

Gentiana septemfida - Fall Gentian

late summer-early fall

deep blue

Geranium spp. - Dwarf Hardy Geranium

all summer

purple, pink or blue

Iris pumila - Dwarf Bearded Iris

late spring

variety of colours

Iberis sempervirens  - Evergreen Candytuft

late spring

white

Leontopodium alpinum - Edelweiss

early summer

white

Papaver alpinum - Alpine Poppy

late spring through summer

white, yellow,

orange or pink

Penstemon spp. - Dwarf Beardtongue

early summer

pink, purple, blue or white

Phlox subulata - Moss or Creeping Phlox

late spring/early summer

pink, blue, red or white

Potentilla spp. - Dwarf Cinquefoil

late spring/early summer

yellow

Primula spp. - Dwarf Primrose

spring

pink, purple or white

Pulsatilla vulgaris - Pasque-flower

spring

purple, pink, red or white

Saponaria ocymoides - Soapwort

early summer

pink

Saxifraga paniculata - Encrusted Saxifrage

early summer

mostly white

Saxifraga X arendsii - Mossy Saxifrage

spring

white, pink or red

Sedum spp. - Stonecrop

summer

yellow, pink, red or white

Sempervivum spp. - Hens and Chicks

all season (foliage)

white, pink or red

Thymus spp. - Creeping Thyme

summer

purple, pink or white

Veronica spp. - Speedwell

late spring/summer

blue

Viola spp. - Violets

spring/early summer

blue, purple or white

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Common rock garden plants include (top to bottom, left to right) creeping phlox, thrift, dwarf broom, pinks, saxifrage, bellflower, dwarf columbine, dwarf geranium and pasque-flower

Rock Garden Construction

A rock garden should be a fair representation of an alpine environment.  Bearing this in mind, there are a few criteria which should be followed.

An open area is the best site for a rock garden since alpine areas are rarely sheltered.  In warm regions, it is best to position the rock garden so it is sloping to the east or north to avoid ‘baking' these cool-loving plants.  In colder areas, a southern exposure is fine.

 ImageImageImage

Some scenes from the Memorial University Botanical Garden of Newfoundland, Canada

The type of rock you choose for your rock garden is up to you.  However, one of the most common mistakes made by rock garden beginners is choosing a wide variety of rocks.  It is far better to stick to just one type of rock, such as sandstone, limestone or granite.

Also try to use weathered rock.  Rocks newly dug from below ground level often look "new" and thus are not very natural when you consider a rock garden is supposed to duplicate an exposed, eroded mountainside or rocky outcrop.

Another common mistake when making a rock garden is placing similarly-sized rocks at even intervals on the surface of the ground.  A rock garden is a garden on rock, not rocks on a garden.  To maintain a natural look, rocks should be irregularly placed and be of irregular size.  Be sure not to place all large rocks at the back and small in the front, but to mix and match.  If terraces are made, don't make them all even in slope or size.  Make some slopes steep, others gentle and vary the sizes of each terrace.

Rocks should be buried to a sufficient depth (at least 1/3 of their size should be below-ground) to keep them stable.  If only laid on the surface, they shift during the frosts of winter.

Soil

This is very important, as most rock garden plants prefer well-drained soil.  A general rock garden mix is:

  • 1 part topsoil
  • 1 part organic material (peat, compost and/or leaf mould)
  • 1 part 3/8" chip stone or coarse sand

Alpine plants naturally grow in nutrient-poor soils.  Therefore, it is very important not to over-fertilize your plants.  Too much fertilizer will result in weak, spindly growths which are often prone to excess winter damage or at the other extreme, plants that flower themselves to death.  It is better to use slow-release, organic fertilizers, such as old manure, old compost or bonemeal, rather than just chemical fertilizers. If gardening in acidic areas, you can also lightly dust the entire surface of the rock garden with lime in mid to late September.

Mulch

A 2 - 4 cm mulch of 3/8 to 1/2 inch chip stone is highly recommended.  It can serve several purposes:

  • it slows moisture evaporation from the soil
  • it keeps soil temperatures even
  • it slows the growth of weeds
  • the problem of frost heaving in spring is lessened
  • muddy soil will not spoil the ground-hugging flowers

 ImageImageImage

Examples of Campanula garganica, Gentian angustifolia and Saxifraga caespitosa growing through a stone-mulch layer

Watering

Rock gardens, like all gardens, require regular watering especially during dry weather.  Do not give the plants a light sprinkling every day as this will only encourage plants to produce roots close to the surface rather than deep down.  Shallow-rooted plants are more prone to frost heaving.  A thorough watering once a week is the best method to use.

 ImageImageImage

Examples of some suitable dwarf conifers include Picea abies 'Echinoformis', Tsuga canadensis 'Nana' and Picea mariana 'Nana'

Winter Protection

Many alpine plants are evergreen or semi-evergreen in nature.  For these plants, winter protection is advisable.  If you live in an area of continual snow-cover, no additional protection is required.  However, we are not all that fortunate.

In wetter areas, evergreen boughs are ideal since they trap blowing snow and do not compact into a sodden-mass.  In dry winter areas, you can use leaves, straw or hay as winter protection.  Remember, winter wetness is the #1 killer of rock garden plants!

Small evergreen shrubs in the rock garden can be protected with a wrapping of burlap or a teepee of boughs.  Deciduous shrubs can have their branches gently tied together with a soft string or old pantyhose.

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Some more scenes from the Memorial University Botanical Garden in St. John's, Newfoundland, Canada


  About Todd Boland  
Todd BolandI reside in St. John's, Newfoundland, Canada. I work as a research horticulturist at the Memorial University of Newfoundland Botanical Garden. I am one of the founding members of the Newfoundland Wildflower Society and the current chair of the Newfoundland Rock Garden Society. My garden is quite small but I pack it tight! Outdoors I grow mostly alpines, bulbs and ericaceous shrubs. Indoors, my passion is orchids. When not in the garden, I'm out bird watching, a hobby that has gotten me to some lovely parts of the world.

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Discussion about this article:
SubjectTopic StarterRepliesViewsLast Post
Inside Out Flower loessgardener 0 2 Aug 20, 2012 11:28 AM
rocks steadycam3 0 10 Mar 31, 2012 3:34 PM
Yea, there's hope for my garden's slope. Kerni 1 20 Mar 31, 2012 5:02 AM
Wow Leehallfae 1 10 Apr 6, 2011 8:32 PM
Great article art_n_garden 1 24 Apr 4, 2011 10:35 AM
Dwarf Columbine Oberon46 0 12 Apr 4, 2011 8:11 AM
Thank you - just what I needed to know! carrielamont 6 56 Apr 2, 2011 7:51 AM
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