Plants For Bog Gardens: How To Build A Bog Garden
By: Susan Patterson, Master Gardener
Nothing beats the natural appeal of a bog garden. Most climates are suitable for growing bog garden plants. They can be designed in various ways based on your landscape and personal needs. Keep reading to learn more about how to build a bog garden.
What is a Bog Garden?
Creating a bog garden in your landscape is an enjoyable project that allows you to experiment with different plant species. So exactly what is a bog garden anyway? Bog gardens exist in nature in low-lying areas or around ponds, lakes, and streams. Bog garden plants love overly moist soil, which is waterlogged, but not standing. These marshy gardens make a lovely attraction in any landscape and can quickly turn an unused, water-logged spot in the yard into a wonderful scenic attraction.
How to Build a Bog Garden
Constructing a bog garden is not a difficult task. Choose a site that receives at least five hours of full sunlight. Dig a hole that is about 2 feet (61 cm.) deep and as wide as you would like your garden to be.
Line the hole with a sheet of pond liner and press it down so that it contours with the hole. Leave at least 12 inches (31 cm.) of liner exposed to accommodate for the bog settling. This edge is easy to hide later on with mulch or small rocks.
In order to keep the plants from rotting, it is necessary to poke drainage holes around the edge of the liner, one foot (31 cm.) below the soil surface. Fill the hole with a mixture of 30 percent coarse sand and 70 percent peat moss, compost, and native soil. Allow the bog to settle for one week and keep it well watered.
Choosing Bog Garden Plants
There are many perfect plants for bog gardens that will naturally adapt to the moist environment. Be sure that you select plants that are appropriate for your growing region. Good choices for a bog garden include some of the following beauties:
- Giant rhubarb– has massive, umbrella-shaped leaves
- Giant marsh marigold– grows up to 3 feet (1 m.) tall with beautiful yellow flowers
- Flag iris– can be purple, blue, yellow, or white with tall stalks and dark green leaves
Other plants for bog gardens include carnivorous species such as Venus flytrap and pitcher plant. Many woodland plants feel right at home in the boggy environment as well. Some of these include:
- Joe-pye weed
- Blue-eyed grass
Be sure to put taller bog plants in the back of your bed and provide plenty of water.
Container Bog Garden
If your space is limited or you are not interested in excavation, consider a container bog garden. A bog garden can be created using any number of containers including whiskey barrels, kiddie swimming pools, and more. Virtually, any relatively shallow container that is wide enough to accommodate some plants will do.
Fill 1/3 of your chosen container with gravel and put a mixture 30 percent sand and 70 percent peat moss on top. Wet the planting medium completely. Let your container bog garden sit for one week, keeping the soil wet.
Then, place your bog plants where you want them and continue to keep the soil wet. Put your bog garden container where it will get at least five hours of daily sun.
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The astilbe flower is promoted by many garden centers for shade gardens. However, without an ample supply of moisture, these late spring through summer flowers will never reach their glorious potential. Astilbes are a slow-growing perennial, so unless you’re planting a large group, start with potted plants.
Depending on the variety, their height ranges from 6 inches to 5 feet. In spite of the astilbe’s need for abundant moisture (dry spells will induce dormancy), some drainage during the winter months is necessary. Astilbes are heavy feeders, so regular soil amendment and fertilizer is important.
How to make a bog garden in a permanently wet area.
Providing the area where you are going to plant bog plants isn't flooded, stagnant or smelly. It is really easy to select bog plants and create a bog garden. Most plants are the same marginals you see around the edges of garden ponds and I have listed a few lower down on this page.
- Planting plan. The same rules apply, as for planting flower borders. Plants look better in groups with the taller plants at the back, low growing in the middle with the ground cover plants in the front.
- Select plants to tolerate sun or shade. When selecting plants check tolerance to shade and position the bog plants appropriately.
- Hard Landscaping, can be as simple or as complex as you want, Simple is probably best, let the plants be the main focus. Timber Bridges can look good and add interest. Stepping stones placed through the bog area will make it easier to plant and maintain your bog garden without getting covered in mud. The stepping stones will also stop the wet soil getting compacted by footprints.
- Seating area. If you are going to include a paved area for seating. Bear in mind on warm evenings the bog area will attract those irritating little insects known as Gnats On the plus side though, the bog plants will also attract more welcome wildlife for you to sit and watch.
- A bog garden will not solve your water-logging problem, but it will make the boggy area look better, interesting and usable.
Bog garden Design and Plants
No water garden is complete without a bog garden as some of the most beautiful and interesting plants thrive in such situations. Many ponds and lakes have a natural perennially damp surround which requires no more attention before introducing plants than to remove unwanted weeds.
If the pond is fed by a natural water supply, it is usually possible to channel the overflow into surrounding land, thus producing an area which is permanently moist without being waterlogged. Alternatively, any low-lying site with a clay subsoil can be periodically flooded over with water to produce a bog garden. During the winter months, rain will supply all the moisture that is required as most bog plants are then dormant.
To make a bog garden on raised ground or where the drainage is very free, creates a different problem which, however, can be overcome with a little effort. Excavate the site to a depth of 38cm (15in) and line the area with poor quality concrete consisting of 12 parts of ballast to 1 part of cement or even weaker, or cover the base with slates, tiles or asbestos sheets slightly overlapping. Another idea is to line the base with a single layer of 500 gauge polythene sheeting perforated in a few places so that it allows water to leak away slowly.
Whatever method is employed, put 6-8cm (23in) of stones or pebbles over the lining to provide adequate drainage. Cover these with a layer of peat tailings or old turves turned upside down. Replace the soil, incorporating liberal quantities of peat, manure or other fibrous material to hold the moisture during times of drought. When finished, the top soil will look like any other herbaceous border, but the roots of the plants will feel the influence of the water, and such conditions should produce an ideal bog garden. Although it is important to water the area in dry weather, it is equally important never to allow the soil to become waterlogged.
Suitable plants There is a wide range of plants suitable for the bog garden. Some of the more popular and interesting kinds include the aconitums (monkshood). The most commonly grown species is A. napellus, with finely cut leaves and purplish-blue flowers, its variety bicolor, with blue and white flowers, and ‘Newry Blue’, flowering June-July on 1-1.3m (3-4ft) stems.
Aruncus sylvester (goat’s beard) if space permits, is a wonderful plant for the back of the bog garden, with large plumes of creamy-white flowers in June and foliage very similar to that of the astilbes and growing to 1.3-1.6m (4-5ft). The numerous varieties of astilbe make excellent bog garden plants, but unfortunately they are frequently grown in dry borders with inadequate moisture, where they never acquire their full splendor. Some of the most popular varieties include: ‘Deutschland’, pure white, ‘Fanal’, deep red with reddish foliage, ‘Koblenz’, rose, ‘Red Sentinel’, very deep red and ‘Rhineland’, bright pink.
The native marsh marigold (Caltha palustris) in both its single and double-flowered forms, is a fine plant for really moist soils. It makes a bold splash of yellow in spring.
Gunnera manicatais probably the most impressive bog plant it is possible to grow in this country, but it is only suitable where there is ample room, as in a large water garden. The foliage resembles enormous rhubarb leaves, often reaching 2.5-3.3m (8-l0ft) in diameter, on stems 3.8m (12ft) or more in height. The flowers are brown—borne in heads about m (3ft) long and something like a bottle brush in appearance. Gunneras require plenty of moisture during the growing season but must not become waterlogged, especially during the winter months, when it is necessary to give the crowns protection by packing the dead leaves over the roots. Extra protection with straw or leaves should always be added in very severe weather.
No garden is complete without hemerocallis (day lily). The species come from Asian riversides and will grow anywhere in the bog garden, in shallow water, in shade or full sun, in heavy wet soil or dry sandy situations. Many hybrids have been produced, giving a wide variety of color from pale yellow to deep red and a flowering period from June to September. Given ample room for development, the plants may be left undisturbed for years. A vast range of hybrids include: ‘C. P. Raffill,’ 0.7m (lift) apricot flowers, July-August `High Tor,’ 2m (6ft) or more in height, yellow flowers, June-July ‘Pink Damask,’ rich pink, and ‘Hiawatha,’ 0.7m (2 1/2ft), copper-red.
Hostas are invaluable semi-shade plants with leaves in various shades of green or green and silver or gold variegations and pale mauve or white flowers. Species include H. fortunei alba, yellow leaves edged with green H. sieboldiana, blue-green foliage H. undulata, large oval leaves H. minor, 30-38cm (12-15 in), pale green leaves and white flowers.
Iris kaempferi and its forms are the most notable of the bog iris. Natives of Japan they are grown beside the paddy fields which are flooded during the summer months but drained in the winter, thus producing ideal growing conditions. As they are lime haters, they must have adequate peat or leaf mold in the soil. These plants are rarely sold as named varieties, but usually as the ‘Higo Strain’ of hybrids.
Lysichitum americanum, the skunk cabbage, indigenous to North America, has large bright yellow arum flowers in April, before the leaves, which make a bold show at the pool side during the summer months. L. camtschatcense from Japan has white flowers and is less vigorous than its American counterpart.
Bog primulas provide some of our best waterside perennials, especially when grown in semi-shade with a background of moisture-loving ferns. Among the best are P. florindae, 0.7m (2.5 ft) sulphur-yellow flowers, June-July P. japonica splendens, crimson-purple, May-June P. japonica ‘Postford White’, an outstanding candelabra type with white flowers P. pulverulenta ‘Bartley Strain’, rose-pink flowers, May-June and P. viali, with mauve flowers, which has bright red buds before opening.
Moisture-loving ferns make an excellent background for bog and water gardens with some shade. Matteuccia struthiopteris, the ostrich feather fern has symmetrical 1m (3ft) long fronds like a shuttlecock. Onoclea sensibilis (the sensitive fern) thrives in shade and moisture and has pale green fronds, 0.3-0.4m (1-1.5 ft) long Osmunda regalis the royal fern is a noble plant, easily grown if given an adequate water supply. When well established it reaches 1.6-2m (5-6ft) in height and will set off any bog or water garden.
Create a bog garden
Our short how-to video shows you how to make the most of damp patches of ground in your garden.
Early spring to late summer is the best time to create a bog garden as the roots have time to get established, in the autumn when food starts to become scarcer they have more chance of being eaten. However, if you put one in autumn, this will create habitat and shelter for animals over the winter.
Your bog garden can be created as an addition to a pond but will work equally well as a standalone feature in low lying areas, for example a badly drained corner.
You can even make one in a container – line half a barrel with punctured plastic (you could use old ripped plastic that’s no use for anything else) and you’re good to go. Or why not fill in an old or leaky pond?
Clay soils that are naturally damp are ideal, but if you only have free draining soils, these will work too, as long as you use a liner and introduce top soil.
- Outline the area where you want your bog garden to go using rope or hose.Make sure you’ve chosen a location away from overhanging trees as you need as much sun as possible.
- Dig a shallow hole 45-50cm deep. Any deeper and you’re getting towards a very a big hole… 45-50cm is enough for most people to dig in the garden and will accommodate the roots of most damp loving perennials (except perhaps Gunnera!) Once lined, pierce with a fork for drainage if using undamaged liner.
- Add a 3 cm layer of grit or gravel.This will help prevent the soil from blocking the drainage holes.
- Put the soil back in the hole, trim back the liner and mix in just a small amount of old compost. You don’t want too many nutrients as this will make the fast growing plants of your bog garden hard to control.
- Plant up your garden and keep watering them until established, if they are drying out (if not, just leave them be). Leave the area to get naturally waterlogged over winter.
Bog Plants – Some of our most unusual and beautiful native species!
What is a “bog plant” ?
In simplest terms, bog plants are plants species that grow in bogs!
Well then, what is a bog? Is it a swamp?
A bog is a specialized habitat, generally a wetland that has accumulated peat. Acidic low-nutrient water occurs at surface level of bogs. Because of this, plant growth and decomposition of organic materials is very slow, and the peat can be several feet deep.
A bog is not a swamp swamps are wooded wetlands. You will not find trees growing in a bog.
What is “peat” ?
Peat is semi-decomposed, dead plant material, mostly composed of sphagnum and other mosses. This dead material is acidic and very absorptive. It holds a lot of moisture.
So, what kind of plants grow in bogs?
There are many plants that grow in bogs, and many of the plants are endemic to bogs (meaning they only occur in bogs). One classification of plants that are perhaps the most famous group of bog plants are carnivorous plants. Yes, plants that eat insects! In Pennsylvania’s boglands, you can find sundews and northern purple pitcher plants these are insect-eating plants, along with the venus flytrap.
Aside from carnivores, some of our most beautiful flowering plants can be found growing in bogs, such as the various species of bog dwelling orchids. Ladies’ tresses, pogonia, and grass pink orchids blooms from summer to fall in a bog.
Bog plants do not need a lot of nutrients from the soil, and can tolerate acidity and excess moisture. This is why carnivorous plants often live in bogs — they find nutrients through consumption of insects.
One of our common holiday food plants grows in bogs too: cranberries! It is not carnivorous, but not only tolerates the conditions of the bog, but thrives in it.
With such special requirements, can I grow bog plants at my house?
YES, YOU CAN! And believe it or not, it really is not very hard! You can create a container bog garden!
All you need is a large pot or container (start with something at least 12” diameter). If there are holes, plug them up (these bog plants don’t require much drainage). I often put a hole in the side of the pot about three quarters up from the bottom to prevent overflowing in rain.
Peat can be purchased at just about any garden center or hardware store. Buy plain peat moss, not something with added fertilizers, etc. Then, get plain perlite (coarse is good) or sand. Create a mix of about 80% peat and 20% perlite or sand fill your container FULL, so it is humped up in the middle. Plant your bog species into the pot. Use mosses from your garden to decorate the surface (just remove the soil from their undersides).
Water with RAIN or DISTILLED water only (no tap water, no spring water, etc). Keep moist, do not allow your bog garden to become too dry. Most bog species prefer full sun (6+ hours). In winter, sink it in your garden soil or mulch to the rim, and cover with leaves or pine bows and place in an area where it will receive snow and rain. An unheated, but attached garage or room can serve as a place to store your bog garden for winter.
What bog species do we have available right now?
Sarracenia purpurea var. purpurea ‘Jersey Girl’ – ‘Jersey Girl’ Northern Pitcher Plant
A lovely selection of our northern purple pitcher plant featuring dark purple pitchers with chartreuse green veining originates from near Ocean City, NJ. This plant has specialized, modified leaves that form pitchers where insects get trapped, drowning in the water caught in the pitchers during rain. Digestive enzymes are released, and the insects are digested, and their nutrients absorbed through the plant tissue. Unusual but interesting flowers up to 12 inches tall arise in early summer.
Drosera filiformis – Thread leaf Sundew
This sundew species has long, thread-like leaves up to 6 inches tall covered in red, sticky tentacles. New leaves emerge curled like fiddle-heads. Each tentacle has a sticky glue-like sap that acts as both an attractive lure for potential prey, and a sticky trap for capturing prey. Insects land on the sticky tentacles and find themselves stuck and likely burning from digestive enzymes that the plant releases. Nutrients from the insect are absorbed straight through the leaves into the plant. You will notice tiny pink flowers throughout the summer.
Drosera intermedia – Spatulate Leaf Sundew
The spatulate leaf sundew is similar to thread leaf sundew, but much smaller, and different in form. This small sundew has spoon shaped leaves, with all the tentacles arranged on the round ends of each leaf. Like with the thread leaf species, you will notice tiny pink flowers throughout the summer.
Dionea muscipula – Venus Flytrap
While not native to Pennsylvania, this famous carnivore is native to the Carolinas (in a very small natural range of about 60 square miles) and just has to be a part of any bog garden! Though a species of more southern origin, the plant is hardy to zone 6 and will usually overwinter with the minimal protection.
Spiranthes odorata – Fragrant Ladies’ Tresses orchid
This is a lovely, dainty, and delicate, fall-blooming orchid that is among the easiest to grow! While not very exciting most of the season, the little white flowers emerge in early fall and will continue blooming until frost. If you get close to them, you will notice their sweet smell. The flowers are arranged in a spiral pattern along the stem, very cool little plant!
Xyris caroliniana – Carolina Yellow-eyed Grass
What a fascinating and cute little plant to complement any bog planter. Tiny, iris-like leaves and adorable yellow flowers that open in the sunshine. It seems every day a new little blossom opens on the “ball” at the end of each flowering stem. This plant is not a true grass, but is related to them.
Pogonia ophioglossoides – Rose Pogonia Orchid
This late spring blooming orchid is a simple charmer, often having just one (maybe two to three) beautiful pink flower on its 4 to 8 inch stems. It will spread by rhizomes, making it an easy one to propagate and move to other bog dishes or share with friends! Or, allow it to fill out a pot by itself for a fantastic display!
Andromeda polifolia – Bog Rosemary
Now, here is a very unusual plant! Unusual in this list, because it is the “upright shrub” listed. Unusual in its genetics, because it is the only member of its genus. Unusual in appearance, as it looks just like culinary rosemary-but it isn’t, and it isn’t even related. Also, unusual in that, unlike most of these bog species, this one appreciates cool temperatures and some shade. While incredibly cold hardy (to zone 2), it is not very heat tolerant, and would probably die anywhere warmer than zone 6. Provide afternoon shade for this species in the dog-days of summer.
Calopogon tuberosus – Grass Pink Orchid
Another pretty orchid to add some charm and grace to your bog planters! This one can grow over 2 feet tall, and feature many magenta to purple flowers on its stems during the summer. Long, grass like leaves grow out of underground corms. The plant will slowly multiply by creating more corms as it ages. Very pretty!
Vaccinium macrocarpon – cranberry
Yes, that’s right, the same cranberry we make sauce out of! You have seen the commercials, with cranberries floating in the bog, right? Well, that is a cranberry farm, a manufactured bog that is intentionally flooded to harvest the cranberries, and to protect them over the winter (yes, they rest under the ice all winter). You do not need to that, of course! The cranberry will happily grow in a bog container, spilling over the sides, and even making berries. The berries add a cool visual appeal to the planter, and also can be eaten, or left for birds and rodents to enjoy.
Bog for Specialized Plants
Growing plants native to sterile acid bogs requires a different approach from the one I took in my garden. The environment of a true bog is unlike a low, wet woodland or meadow. A bog forms slowly in a glacial lake bed with the help of specialized mosses called sphagnum that grow inward from the edges of the lake. As they grow, the lower portions of their stems die but remain attached as the upper stems branch and spread, creating an interwoven mat.
At first the moss floats on the surface of the water. But as the mat grows and decays, it deposits peat on the lake bottom. As the sphagnum spreads outward, the floating mat becomes thick enough for other plants to take root and grow. Eventually, the sphagnum covers the entire lake, and the floating mat of vegetation is dense enough to support flowers, shrubs and even trees.
This kind of bog is called a quaking bog. Walking on it is like walking on a squishy waterbed. The ground trembles or quakes. To re-create this environment in your yard, you need to provide a sterile substrate on which the plants can grow. Clean, medium-coarse sand and peat moss are the best choices. Dig a trench as described in the accompanying chapter. Since most specialized bog plants have sparse root systems, two feet is generally deep enough. I recommend installing perforated pipe in at least two corners of the bog as you may be adding distilled water or rainwater collected elsewhere. A pipe 2 to 4 inches in diameter is ideal. For larger bogs, use the double-pipe system described above.
Fill the excavation with a 50/50 mixture of sphagnum and sand. A living layer of sphagnum at the top of the bog is desirable but may be hard to come by. Carolina Biological Supply Company is a good source. You can reach them at 2700 York Road, Burlington, N.C. 27215 (800) 334-5551.
It is imperative that you let the bog settle for at least a month before planting. The pH of the sand and sphagnum mix and the water need to come into balance before the plants are added. The additional time also allows the soil to settle. If it settles too much after the plants are established, it may bend or break their new roots.
Before planting, wash all the soil from the roots of the new plants to avoid introducing soil-borne microorganisms and worms. If you use live moss, add it after the other plants are in place. The moss is often slow to establish.
Use only rainwater or distilled water in the bog. Tapwater contains minerals and chlorine harmful to bog plants. It is also neutral to alkaline in pH, and bog plants need a highly acidic soil. As with all bogs, consistent water is essential. Bogs are naturally low in nutrients, so do not add fertilizer.
Because it requires so much diligent attention, a specialized bog is not for everyone. Do not waste time and doom plants to a slow death if you are unwilling to manage a true bog garden properly.
Many bog plants, such as pitcher plants, are becoming rare in the wild. If you choose to plant them, purchase them only from reputable dealers who propagate their own plants. Make sure you do not buy wild-collected specimens. Remember that "nursery-grown" does not mean nursery propagated.
A living mulch of sphagnum moss is desirable for an acid bog. Add an additional mulch of pine straw in winter to protect delicate plants, especially in areas where winters are cold and snowfall is erratic. Remove the mulch in the spring to allow the sphagnum to grow.
C. Colston Burrell is an avid plantsman, garden designer, and award-winning author.