Building an outdoor bog garden for pitcher plants and flytraps

Why grow carnivorous plants in the ground

A bog garden puts many plants with similar needs into one large, wet bed, and done well it looks natural ^[1]. The bigger soil mass also buffers the plants. The ICPS Sarracenia guide says that in USDA zone 6 Sarracenia are best grown in artificial bogs in the ground ^[3], and the flytrap guide says an in-ground bog works best for flytraps in zones 7 and 8 ^[4]. Even large pots help for the same reason: they moderate soil temperature and moisture ^[5].

The ICPS points to a past president’s garden in Ontario, Canada, as proof of what bogs can do. His kiddie-pool bogs, in a lake-moderated area rated USDA zone 6B, hold every Sarracenia species and many hybrids, along with flytraps and temperate sundews, including S. psittacina, which is hard to keep outdoors in the northern US ^[2]. Strictly speaking, Sarracenia are fen plants that grow where water moves through the soil, but the ICPS says they do well in artificial bogs ^[3].

Choosing the site

• Sun. The plants that do best in bogs are almost all sun lovers, so the Pacific Northwest page says to pick a sunny spot; a west-facing one is fine in a mild coastal climate ^[1]. In very hot, dry areas Sarracenia pitchers can burn, and some afternoon shade helps ^[3].
• Drainage of the ground around it. A bog in a low spot can flood and wash plants out. Choose level ground or a place that slopes away from the bog ^[1].
• Water supply. In wet regions the problem is too much rain; in drier, hotter places it becomes finding large amounts of pure water for summer ^[1].
• Runoff. Keep garden fertilizers and pesticides from washing into the bog ^[1].

Building the bog

The two ICPS bog pages describe slightly different builds. These steps combine them.

1. Pick a liner. The Sarracenia guide lists molded plastic pond shells, plastic sheeting or pond liner ^[3]; the Ontario bogs are kiddie pools sunk into the ground ^[2].
2. Dig deep. For plastic-lined bogs, the Pacific Northwest page recommends about 1.5 to 2 feet (roughly 45 to 60 cm): a deep bog dries out less, and most of these plants have deep roots. Bigger is better in general ^[1].
3. Make overflow holes. Punch holes near the top of the liner ^[1], or, as in Ontario, a third of the way down the sides of the pool ^[2], so excess water drains out instead of drowning the plants.
4. Fill. A 50:50 mix of peat moss and sand, moistened, with more added over the next few days as it settles ^[1]. The Ontario bogs use pure Canadian peat in the bottom half and a peat and sand mix in the top half ^[2]. See soil for choosing peat and sand.
5. Finish the edges. Any edging or decoration should be non-toxic and must not leach minerals or nutrients into the bog ^[1].
6. Plant. Place small plants where they will not be hidden by tall ones, and avoid straight rows ^[1].

Water

For Sarracenia, the ICPS recommends keeping the water level 7 to 18 cm (3 to 7 in) below the soil surface and adding water on the side opposite the drain; the plants tolerate total immersion for short periods ^[3]. How often you water in summer depends on the depth of the bog. The Pacific Northwest author uses a top layer of live sphagnum as a gauge, watering when it dries, and rarely waters in winter, when the plants are dormant and rain is plentiful ^[1].

The water must be low in minerals. The Ontario garden collects rain from the house roof in a tank ^[2], and the ICPS deck page sets the bar for outdoor Sarracenia at tap water under 100 ppm TDS, or plenty of collected summer rain ^[5]. Details are in water.

Rain can be a problem too. In the Pacific Northwest, heavy late-spring rain beats down small plants and splashes them with soil; the author’s answer is a sloped cover of rigid plastic, which then means watering more often ^[1].

What to plant

The Pacific Northwest author lists the plants that succeeded in his North Vancouver bog ^[1]:

He notes that what the successful plants share is a thick underground storage system, either a rhizome or thick roots, and that his results may not carry over to other climates ^[1]. North Vancouver is mild and wet; elsewhere, hardiness decides. The ICPS hardiness notes by USDA zone for Sarracenia and flytraps are summarized in dormancy; in zone 6, for example, the ICPS suggests concentrating on Carolina and highland Sarracenia such as S. flava, S. oreophila, S. jonesii and S. purpurea subsp. purpurea ^[3]. For cold temperate sundews, the ICPS advice is to choose plants from a climate like your own ^[6].

Darlingtonia is the notable exception. Although native to the Pacific Northwest, it did not do well in the author’s bog, because it wants cooler roots and less sun than a bog gives; he grows it in pots in north-facing spots instead ^[1]. The ICPS Darlingtonia guide agrees that in-ground plantings suit it only where the soil stays below about 27 °C (80 °F) in summer, and shows pots sunk in shaded ground with drains that hold the water about 20 cm below the surface ^[7]. See the cobra lily profile.

Winter in the bog

The Ontario method is the most detailed winter routine on the ICPS site ^[2]:

1. Leave the bog uncovered until winter really sets in, which there is mid-December. Mulching too early can stop the plants going fully dormant.
2. When hard freezes threaten, cut back the Sarracenia pitchers and bury the plants in a deep layer of pine needles, 20 cm (8 in) or more.
3. Let snow cover the needles; it adds protection against freeze-thaw cycles.
4. Uncover in mid to late March, easing plants out of dormancy as nights warm. Needles can act like small greenhouses on sunny days, so timing matters.
5. Leave a thin layer of needles for spring frost protection and to hold moisture in summer.

Pine needles work because a deep layer does not pack down, rot or compost. The same page warns that bark mulch deeper than about 5 cm can compost and go anaerobic, and suggests seed-free wheat or other heavy straw if pine needles are not available ^[2]. The Ontario grower adds that winters are hardest in the middle zones, where plants freeze and thaw repeatedly; plants that freeze solid and stay frozen, or that barely freeze at all, do better ^[2].

For flytraps in zones 7 and 8, the ICPS suggests covering the bog with a few inches of pine needles, row cover or both, and stresses not letting the plants dry out, since freeze-drying is the biggest danger ^[4]. In wet, mild winters, trim off dead growth so fungus does not take hold ^[1]. The dormancy planner gives a month-by-month plan.

Animals and pests

• Diggers. Squirrels, raccoons and skunks dig in bogs for worms and grubs, and squirrels will eat flytrap bulbs. The Pacific Northwest author found repellents, electric fencing and noise ineffective and relied on a removable chicken-wire frame ^[1]. The Sarracenia guide notes that raccoons and squirrels are drawn to standing water and live sphagnum, and shows a caged water tray ^[3]; the Darlingtonia guide shows a water-feature planting that raccoons wrecked ^[7]. Jays uproot newly planted flytraps ^[8].
• Slugs and snails. They eat sundews and Sarracenia flowers. The author used beer traps, copper wire around the bog and pet-safe bait, and kept nearby grass short ^[1].
• Strawberry weevils. Notches in the wings of Sarracenia or Darlingtonia pitchers are the sign; the larvae destroy the rhizome and roots. The fix described is to go out about an hour after dark with a flashlight and pick off the adults every night for a week ^[1].
• Aphids. The ICPS checklist notes that aphids love flytraps and deform the leaves ^[8]; see aphids, mealybugs and scale.
• Bears. Keep garbage and yard waste away, and clip off pitchers overloaded with rotting insects ^[1].

Mistakes the sources warn about

• Building in a low spot that floods ^[1].
• Mulching too early, which can keep plants from going fully dormant ^[2].
• A thin compost or bark mulch instead of a deep, open pine-needle layer ^[2].
• Planting Darlingtonia in a sunny bog ^[1].
• Letting fertilizer or pesticide runoff reach the bog ^[1].
• Letting dormant flytraps dry out under winter cover ^[4].