Perennials With Hollow Pithy Stems That Shelter Stem-Nesting Bees

Australia harbours more than 1,700 native bee species, and a sizeable share of them are cavity nesters. Rather than excavating burrows in the ground, these solitary insects partition the soft interiors of dry plant stems into a chain of brood cells, stocking each one with pollen and nectar before sealing it with leaf fragments or mud. Gardeners who want to support them can look beyond bee hotels and timber blocks, planting perennials whose dead winter stems hold the right kind of hollow, pithy architecture.

In temperate suburbs from Hobart to Adelaide, gardeners are rediscovering the value of leaving stems standing through autumn and early winter. The Perennials in Focus program has spent several seasons evaluating which herbaceous plants reliably produce hollow or pithy stems suitable for reed bees, masked bees, and small carpenter bees. The findings are useful well beyond Chicago, where the trials began, because many of the same species thrive in Australian climate zones.

What follows draws on that trial data alongside Australian field observations, blending horticultural know-how with pollinator ecology. You will find perennials suited to a coastal Sydney courtyard as well as a frost-pocket garden in regional Victoria, with guidance on when to cut back and how to position plants for maximum nesting value.

A useful first step is to understand which bees you are actually trying to host. Australian stem-nesters include Exoneura reed bees, which favour stems with a soft pith that they can chew through, and various Hylaeus species that need pre-formed hollows of around two to six millimetres in diameter. Different perennials support different guests, and matching the two is the heart of thoughtful pollinator garden design.

Why Stem-Nesting Bees Need Hollow Plant Material

Female cavity-nesting bees do not dig soil tunnels the way mining bees do. Instead, they locate a stem of suitable diameter, enter from the broken or cut end, and excavate or rearrange the pith to form individual brood chambers. Each chamber receives a provision mass of pollen and nectar, a single egg, and a partition made of leaf pieces, resin, or mud. A single stem can host a dozen or more developing larvae from autumn through to the following spring.

Hollow-stemmed perennials provide this housing free of charge once flowering finishes. Stems of plants like globe thistle, Joe Pye weed, and blazing star become natural incubators as the pith dries and contracts. Gardeners who tidy too aggressively in autumn can inadvertently remove every available nest site, which is why leaving bundles of cut stems tucked behind a shed or stacked upright in an out-of-the-way corner is now a widely recommended practice.

In Melbourne's inner north, community garden coordinators have noticed steady increases in Exoneura populations where liatris and echinops have been allowed to stand through winter. The pattern is consistent with observations from trials in North America and is one of the reasons the Perennials in Focus network has begun publishing region-specific guidance for Australian conditions.

Best Hollow-Stemmed Perennials for Australian Gardens

Several non-native perennials have proven particularly valuable across multiple trial sites. Liatris spicata produces stiff, upright hollow stems forty to sixty centimetres tall that reed bees readily adopt. Echinops ritro offers similar architecture with the bonus of spherical steel-blue flower heads that attract a wide range of pollinators while in bloom. Helenium autumnale, Monarda didyma, and the taller cultivars of Eutrochium purpureum all dry into usable nesting habitat.

Less common choices include Dipsacus fullonum, which acts as a biennial but reliably produces thick hollow stems loved by larger Hylaeus species. Phlox maculata, with its spotted stems, has a notably pith-filled interior, and Filipendula ulmaria softens wilder corners while doubling as nesting material. Solidago rigida, sometimes overlooked in favour of its leggier relatives, has the firmest hollow architecture of the goldenrods trialled.

In Brisbane's humid subtropics, success with these plants depends on sharp drainage and adequate airflow to prevent stem rot. Gardeners on the coastal strip north of Sydney report similar results, particularly when plants are cut back only partway, leaving ten to twenty centimetres of stem above ground level as a deliberately exposed nest cavity.

Australian Natives With Pithy Centres

Native options should not be overlooked. Xanthorrhoea species, while slow growing, develop a pithy crown that native stingless bees occasionally investigate, though they are not classic stem-nesters. More useful are several Lomandra cultivars, whose older flowering stems dry into hollow tubes favoured by small solitary species in Canberra gardens. Dianella caerulea and Dianella revoluta hold their seed stems into winter, and although the interior is not always fully hollow, the partial pithy core is used by smaller Hylaeus bees.

For gardeners in Western Australia, local species of Stylidium and Patersonia offer similar roles, particularly in bushland-style plantings around Perth and the South West. A mixed border that combines one or two native pithy-stemmed plants with the more dramatic architecture of Liatris or Echinops tends to attract the broadest mix of native bees across the warmer months.

Managing Stems Through the Seasons

Timing of cutback is everything. The recommended approach is to wait until early spring, just as new basal growth appears, before cutting last year's stems down to ground level. This exposes the hollow interiors at the moment when overwintering adult bees are beginning to emerge, ensuring they are not trapped inside drying stems that have not yet been opened up.

For gardeners who prefer a tidier winter look, stems can be cut in late winter and bundled upright in a sheltered spot against a fence or under a dense shrub. The bees emerge from these bundles in their own time, and the gardener regains a cleaner winter border. The Perennials in Focus team publishes snapshots-e-h of trial plots showing how different cutback timings influence bee recovery rates.

Some councils in New South Wales operate under biodiversity overlays that restrict the removal of standing dead material in certain zones. Gardeners should check local guidelines, particularly in bushland interface areas, before extensive cutting. In Victoria, the Native Vegetation Framework encourages retention of habitat features, and most local authorities take a relaxed view of leaving hollow stems in private gardens.

Siting and Soil Conditions Across Climate Zones

Perennials for stem-nesting bees prefer the same conditions that suit pollinator-friendly gardens more broadly: full sun, reasonable drainage, and a soil that does not waterlog in winter. In Perth's sandy gravels, echinops and liatris thrive with minimal supplementary watering once established. In Adelaide's Mediterranean climate, deep mulching and a single deep soak every two weeks during the first summer is usually enough.

Gardeners in Sydney's coastal suburbs often need to lift clay-based soils with gypsum and coarse organic matter before these perennials will perform well. Hobart and parts of Melbourne present the opposite challenge, with cool summers and high rainfall encouraging rot in stems that have not been given enough airflow. Spacing plants generously and avoiding overhead irrigation are the simplest remedies.

Container gardeners on apartment balconies in Brisbane and Melbourne can still host stem-nesting bees by growing compact Liatris cultivars or dwarf Helenium in deep pots, leaving the previous season's stems in place across winter in a sunny corner. Statistical work on emergence patterns, including a mathematical probability model that links stem diameter to bee size, suggests even small plantings can support a handful of nesting females each year.

Pairing Perennials With Other Bee Habitat

A diverse planting outperforms a monoculture every time. Pairing hollow-stemmed perennials with early-flowering ground covers, late-flowering salvias, and a shallow water source creates a season-long buffet alongside secure nesting habitat. Native ground covers such as Chrysocephalum apiculatum and Scaevola aemula extend floral resources into the shoulder months when stem-nesters are most active.

Adding a few pieces of untreated hardwood with pre-drilled holes complements rather than replaces plant-based habitat, because the two substrate types attract slightly different bee communities. Avoiding insecticide use, particularly systemic neonicotinoids, is the single most protective measure a gardener can take.

Perennial	Stem type	Stem diameter	Best climate zones	Bee types supported
Liatris spicata	Hollow, upright	4–8 mm	Cool to warm temperate	Exoneura, small Hylaeus
Echinops ritro	Hollow, stiff	5–10 mm	Temperate, Mediterranean	Reed bees, Hylaeus
Helenium autumnale	Partly pithy	4–7 mm	Temperate	Small reed bees
Eutrochium purpureum	Hollow, tall	6–12 mm	Cool temperate, moist	Larger Hylaeus
Lomandra longifolia	Hollow, leathery	3–5 mm	Subtropical, temperate	Tiny reed bees
Dianella caerulea	Partial pith	3–6 mm	Most Australian zones	Hylaeus, Exoneura
Dipsacus fullonum	Thick hollow	8–15 mm	Cool temperate	Large Hylaeus

Browse the full Perennials in Focus plant database to compare regional trial results, then plan a winter cutback schedule that keeps your stems standing just a little longer this year. Share your observations with local native bee groups, and your garden will be hosting new generations of solitary bees before the next flowering season begins.