Why 70% of Native Bees Nest Underground — And How to Build Habitat They’ll Actually Use

Walk into any garden center and you’ll find bee hotels prominently displayed — bundles of hollow tubes and drilled wood blocks meant to give native bees somewhere to live. The premise makes intuitive sense: bees need nesting spots, bee hotels provide nesting spots.

Except roughly 70% of North America’s native bee species can’t use a bee hotel at all. They nest underground. Mining bees, sweat bees, squash bees, and cellophane bees excavate tunnels beneath your garden soil, spending up to eleven months per year below the surface [1]. No hollow tube helps them.

What makes this consequential for garden planning: the practices most likely to harm these bees — thick mulch, weed barrier fabric, routine tilling, early spring cleanup — are the same ones many gardeners consider responsible care. Meanwhile, the practices that genuinely help them cost nothing extra and require less work than a tidy bed.

This guide focuses on the ground-nesting majority: who they are, what soil conditions they actually require (down to specific sand content), why well-intentioned gardening quietly blocks them, and exactly what to change. It also covers which plants deliver the most value for specialist native bees — and why native plant species aren’t always interchangeable with their ornamental cultivars.

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Meet the Underground Majority

Ground-nesting bees include some of the most diverse and ecologically important native bee groups in North America: mining bees (Andrena, with over 450 species), sweat bees (Halictidae, the most species-rich bee family on the continent), squash bees (Peponapis), cellophane bees (Colletidae), and many bumblebee species. Rutgers NJAES Extension puts the ground-nesting figure at approximately 70% of wild bee species [1]. Utah State University Extension goes higher: “at least three-fourths of our native bee species nest in the ground” [2].

Most of these bees are solitary. Each female selects a site, excavates her own tunnel, provisions individual cells with pollen and nectar, lays a single egg on each, and seals the entrance. She repeats this process dozens of times across a short adult life — typically four to eight weeks above ground. The rest of the year, up to eleven months, her offspring develop underground through egg, larva, and pupa stages before emerging the following season.

Mining bees in the genus Andrena dig tunnels 6–7 inches deep, with lateral cells branching from a central vertical shaft. Each cell is waterproofed with a secretion from specialized abdominal glands — a precise adaptation that keeps eggs viable through variable spring soil conditions. Common ground-nesting species you may already have in your garden include bumblebees, sweat bees (Halictidae), miner bees (Andrena), and cellophane bees — all of them identified by UGA CAES entomologists as ground-dependent nesters [10].

Because ground-nesting bees spend nearly the entire year underground, any disturbance at any time of year can kill developing larvae. This is why no-till farming shows such consistent benefits for pollinators: Penn State Extension cites research showing farms using no-till practices had triple the squash bee visitation compared to conventionally tilled operations [7].

What Ground-Nesting Bees Actually Need from Your Soil

The idea that any patch of bare dirt will attract ground-nesting bees understates how specific their requirements actually are. A 2025 study in Ecology and Evolution examined Andrena vaga nesting sites in urban environments and found that high-density nesting aggregations averaged 39.3% bare ground coverage, compared to 16.9% in low-density areas — and far less in uncolonized control sites [3].

Soil composition mattered as much as bare surface area. Nesting sites averaged 77.2% sand content — firmly sandy loam territory — with warmer soil temperatures at depth, lower moisture levels, and reduced penetration resistance compared to unoccupied nearby soil [3].

The mechanism works like this: mining bees begin nest-building as soil temperature triggers their emergence in early spring. Sandy soil drains excess moisture faster, which keeps it warmer. Warmer, softer soil is exponentially easier for a 12mm bee to excavate than cold, compacted clay. South-facing slopes receive more direct solar radiation and warm faster in March and April than level ground or north-facing aspects. A bee on a shaded, clay-heavy site in early April may be unable to excavate at all, while a neighbor on a sunny sandy slope is already provisioning her first cells.

Overhead irrigation also disrupts nesting behavior in a less obvious way: watering during daylight hours saturates the top inch of soil where nest entrances are located, washing away the chemical and visual cues that ground-nesting females use to relocate their burrows after foraging trips. USU Extension notes that bees irrigated during daylight hours “lose nest entrance cues and become disoriented” [2].

One important nuance from the 2025 research: clearing vegetation to create a bare patch did not automatically attract bees to new areas. Proximity to existing nesting aggregations appears to matter — bees tend to nest where other bees are nesting [3]. A bare patch adjacent to an area where ground-nesting bees are already active is far more likely to be colonized than one in a yard with no existing population.

Why “Good Gardening” Is Quietly Blocking Them

Four common practices — all considered responsible gardening — consistently create barriers for ground-nesting bees:

Thick mulch. A UC Santa Cruz study found a statistically negative correlation between the mulched area of a garden and the number of bee species present (Quistberg et al., 2016) [6]. Even a shallow layer of wood chips raises the compaction of the soil surface, alters its thermal profile, and prevents females from digging entrance tunnels. Utah State University Extension is direct: thick bark mulch, wood chips, and loose gravel are impenetrable to ground-nesting bees [2].

Weed barrier fabric. USU Extension describes landscape fabric as “just as impervious for a bee as pavement” [2]. Fabric blocks sunlight from reaching soil, suppresses the surface warming that triggers emergence, and physically prevents nest excavation. Even if a bee managed to dig through it, she couldn’t re-enter and exit repeatedly throughout her nesting period.

Tilling and digging. Ground-nesting bee larvae can remain underground for up to eleven months. Routine spring bed preparation destroys nests in all development stages. A no-till approach — using a hand dibber for transplants, leaving soil structure intact — dramatically reduces this harm [7]. Penn State Extension notes that farms with no-till practices showed triple the squash bee visitation compared to conventionally tilled operations, a direct measure of how damaging tillage is for ground-nesting species [7].

Overhead irrigation timing. If you must irrigate, do it in late afternoon when most ground-nesters have returned underground. Morning irrigation saturates nest entrances at exactly the moment bees are actively leaving and returning, erasing the chemical trails they use to navigate back to their burrows [2].

Our article on 10 pollinator garden mistakes that drive bees away covers several of these traps in detail, including how well-intentioned planting decisions can undermine the bees you’re trying to help.

How to Build a Bare-Soil Patch That Bees Will Actually Use

Creating ground-nesting habitat doesn’t require a dedicated meadow. A 2×2 foot area is enough to start, though 3×3 feet or larger increases the likelihood of use.

Location: Full sun or south-facing aspect, ideally with a slight slope for drainage. Six or more hours of direct sun per day warms the soil fast enough to trigger nesting and keeps it dry between rain events — both conditions ground-nesting bees require.

Soil: Sandy loam is the target, matching the approximately 77% sand content found at confirmed nesting sites [3]. If your garden runs to clay, amend the top 3–4 inches with coarse builder’s sand (not fine play sand, which compacts). You’re not building a sandbox; you’re reducing penetration resistance so a female bee can excavate.

Management: Leave the patch completely undisturbed — no tilling, no mulching, no raking, no weed barrier. A thin biological crust may develop on the surface over time; this is fine and actually stabilizes the structure. Hand-pull weeds carefully if necessary, disturbing as little soil as possible.

Integration: A bare patch tucked between perennial clumps, along a south-facing foundation wall, or at the base of a garden retaining wall is more likely to be colonized than one in open lawn. Research from UGA CAES suggests that combining floral resources with bare soil patches, positioned near existing bee activity, produces the best results [9]. UGA Extension also specifically recommends leaving “drier patches of your landscape bare of plants” for ground-nesting species that prefer sandy, dry conditions [10].

What not to do: No weed barrier under the patch. No ground cover planted over it. No position under an overhead sprinkler. Colonization may take a full season if your local ground-nesting bee population is sparse — patience matters here.

Leave the Leaves, Leave the Stems

Ground-nesting bees overwinter within an inch or two of the soil surface [5]. A layer of fallen leaves acts as thermal insulation, moderating the freeze-thaw cycles that can kill overwintering larvae and near-surface pupae. Stripping every leaf in autumn — or in an early spring cleanup — exposes these developmental stages to lethal temperature swings.

Penn State Extension provides a practical timing rule: don’t begin spring cleanup until apple trees are blooming in your area — that’s typically when the first mining bees and bumble bees have already emerged from their overwintering sites [5]. A working temperature guideline: once overnight temperatures have held above 50°F (10°C) consistently for two or more weeks, the bulk of ground-emerging bees have moved on.

When you do clean up, relocate leaf piles to garden edges or under shrubs rather than bagging them. Shredding and leaf blowing destroy the physical structure that insulates overwintering insects and may destroy developing chrysalids in the process [5].

Stems matter for cavity-nesters. Roughly 30% of native bees nest in cavities rather than soil [1] — small carpenter bees (Ceratina), orchard mason bees (Osmia), leafcutter bees (Megachile). Many of these species excavate nesting chambers in the hollow or pithy stems of raspberry, sumac, forsythia, roses, and ornamental grasses [2]. Instead of cutting perennials to the ground in autumn, trim them to 12–15 inches. The stub provides a nesting structure for the following season.

If you must clear stems, bundle them and lay them horizontally under a shrub rather than composting. For more on cavity-nesting species — including which bee hotels work, which don’t, and why most commercial designs underperform — see our research-backed guide to bee hotels.

Plants That Actually Deliver: Specialist vs. Generalist Bees

The most important principle in planting for native bees isn’t any single species — it’s a continuous sequence of native bloom from early spring through hard frost. But within that sequence, some plants matter far more than others.

Approximately 25% of native bee species in the eastern United States are pollen specialists (oligolectic): they can only feed their larvae pollen from a single plant family or genus [4]. Specialist bees can visit any flower for nectar, but they must have their specific host plants to reproduce. Without those plants, they disappear from a garden — even a garden full of flowers.

The Asteraceae family — goldenrod, sunflower, aster, coneflower — is the single most important plant family for specialist native bees in North America. Entomologist Jarrod Fowler’s comprehensive documented survey found that Asteraceae supports 62 specialist bee species, more than any other plant family by a wide margin [4]. Here’s the breakdown for the top host plants:

A native goldenrod does far more work for specialist bees than any ornamental variety of the same genus. Modern cultivars bred for showiness — doubled petals, unusual colors, compact habit — often have altered pollen chemistry, reduced pollen quantity, or modified flower morphology that renders them functionally useless to specialist bees, even when they look nearly identical to the wild species. If you’re buying goldenrod or aster, look for straight species rather than named cultivars.

Willow (Salix) deserves special mention as an early-spring lifeline. It blooms in March–April across most USDA zones, delivering critical pollen at the exact moment mining bees first emerge from the soil. An Andrena specialist on willow that finds no willow in flower simply cannot provision her first nest cells [4].

For a continuous bloom sequence across the growing season, these reliable choices cover most USDA zones [1][8][10]:

• Early spring: Native willow (Salix), redbud (Cercis canadensis), serviceberry (Amelanchier), wild blue lupine (Lupinus perennis)
• Late spring: Penstemon, anise hyssop (Agastache foeniculum), golden Alexanders (Zizia aurea)
• Summer: Purple coneflower (Echinacea purpurea), bee balm (Monarda), milkweed (Asclepias incarnata), Joe-Pye weed
• Fall: Goldenrod (Solidago), native asters (Symphyotrichum), mountain mint (Pycnanthemum)

For Southern gardeners in USDA Zones 7–9, UGA Extension recommends American beautyberry (Callicarpa americana), sweet spire (Itea virginica), and Eastern redbud as particularly important for regional native bee communities [10].

I find in my own garden that a single goldenrod clump in early fall — straight-species, not a cultivar — draws more species diversity in a week than anything else I plant all season. The specialist bee activity is visibly different from what I see on ornamental plants nearby.

For a full zone-by-zone breakdown of what to plant and when, our Pollinator Garden Guide on designing a 4-season bloom sequence maps species to bloom windows across USDA zones. It’s the companion planning resource to this habitat guide.

Quick Action Checklist

Frequently Asked Questions

Do ground-nesting bees sting?

Most solitary ground-nesting bees are extremely docile. Unlike honey bees guarding a hive, they have no colony to defend. Mining bees and sweat bees — two of the largest groups — are among the gentlest bees encountered in North American gardens. Males, which often hover near nesting aggregations, cannot sting at all. A female mining bee will only sting if physically pinched or trapped.

Should I remove a ground-nesting bee aggregation in my lawn?

Leave it. Ground-nesting aggregations in lawns are temporary — typically a few weeks in spring — and the bees cause no damage to grass roots or soil structure. They are providing meaningful pollination services to your neighborhood during this period. Moving or treating the site will kill developing larvae underground.

Will any mulch block nesting?

Continuous thick layers of wood chips or bark — even 1–2 inches applied broadly — are sufficient to prevent most ground-nesting bees from excavating. If you want to mulch planted areas, leave unmulched patches of at least 2×2 feet in full-sun areas, and avoid mulching over zones where you’ve observed ground-nesting bee activity.

What if I only have clay soil?

Clay alone is too dense and cold-draining for most ground-nesting bees. Amend the top 3–4 inches of your designated bare patch with coarse builder’s sand to improve drainage and lower penetration resistance. Aim for a consistency that holds its shape loosely when compressed and drains freely within 30–60 seconds after watering.

Are bee hotels useless?

Not entirely. For the roughly 30% of native bees that nest in cavities — mason bees, leafcutter bees, small carpenter bees — a well-designed bee hotel with appropriate tube sizes and proper maintenance can genuinely support reproduction. The issue is that most commercial hotels are poorly designed, lack drainage, and spread disease without annual tube replacement. Our research-backed guide to bee hotels covers what the science shows and how to set one up correctly.

Sources

1. Rutgers NJAES Extension. “Supporting Bees in Your Garden and on Your Farm.” https://njaes.rutgers.edu/fs1280/
2. Utah State University Extension. “Gardening and Landscaping Practices for Nesting Native Bees.” https://extension.usu.edu/pests/research/gardening-for-native-bees
3. Gardein H., Diekötter T., Bloem E., Greil H. (2025). “Barefoot Trees for Bees: Nesting Site Characteristics of the Ground-Nesting Bee Andrena vaga in an Urban Environment.” Ecology and Evolution. https://pmc.ncbi.nlm.nih.gov/articles/PMC12535216/
4. Fowler, J. “Pollen Specialist Bees of the Eastern United States.” https://jarrodfowler.com/specialist_bees.html
5. Penn State Extension. “Delay Garden Cleanup to Benefit Overwintering Insects.” https://extension.psu.edu/delay-garden-cleanup-to-benefit-overwintering-insects
6. UC ANR Bee Gardener Blog. “To Mulch or Not to Mulch: That ‘Bee’ the Question.” Cites Quistberg et al. 2016, UC Santa Cruz. https://ucanr.edu/blog/bee-gardener/article/mulch-or-not-mulch-bee-question
7. Penn State Extension. “What Can We Do to Encourage Native Bees?” https://extension.psu.edu/what-can-we-do-to-encourage-native-bees
8. Penn State Extension (Heather Holm). “Top Gardening Activities to Support Native Bees.” https://extension.psu.edu/heather-holms-top-gardening-activities-to-support-native-bees
9. UGA CAES. “CAES Entomologist Delivers Call to Action: Create More Bee Habitat.” https://fieldreport.caes.uga.edu/features/urban-bee-conservation/
10. UGA CAES Field Report. “Pollinator Habitats.” https://fieldreport.caes.uga.edu/news/6431/