Zone 6 Companion Planting Guide: What I Pair, What I Skip, and When I Plant It
If you garden in Zone 6, you know timing and thoughtful pairings can decide a season. I plan around a typical last frost from late April to mid-May and a first frost from mid- to late October; I then adjust by a week or two for my microclimate. The goal is steady bloom, healthier plants, and stronger stems—without fighting mildew or pests all summer.
How I Think About Pairings
I begin with the site: sun or shade, drainage, and wind determine everything that follows. To keep disease in check, I design for airflow by mixing feathery plants with larger, leafy forms. I layer heights—tall spires in back, mid-border anchors in the middle, and soft edgers up front—so harvest is easy and light reaches what needs it. I also group by water demand: dry-garden classics, such as lavender, belong nowhere near moisture-loving hydrangeas. Finally, I include flowers that feed beneficial insects; Ammi majus, yarrow (Achillea millefolium), and sweet alyssum (Lobularia maritima) are reliable.
My Go-To Guilds in Zone 6
Roses with a Support Squad
Roses with alliums, catmint (Nepeta), lavender (Lavandula), and hardy geraniums. Alliums thread between canes; catmint and geraniums reduce soil splash; lavender invites pollinators and scent. I give each rose a clear base and keep spreaders away from the crown.
Dahlia with Airy Wingmen
Dahlias with cosmos (Cosmos bipinnatus), zinnias (Zinnia elegans), sweet alyssum, and marigolds (Tagetes). Cosmos and zinnias allow light and air to move; alyssum supports hoverflies; marigolds steady the edge. I stake early and keep giant sunflowers a respectful distance.
Peony’s Spring Quartet
Peonies with alliums, bearded iris (Iris germanica), and yarrow. Full sun and drainage suit Zone 6 springs. Iris rhizomes remain exposed; peonies occupy the middle tier; yarrow arrives later with flat umbels for bouquets.
Spring Bulbs That Sing Together
Tulips (Tulipa) and daffodils (Narcissus) with wallflowers (Erysimum) and forget-me-nots (Myosotis). Daffodils discourage browsing; forget-me-nots hide fading bulb foliage. I plant bulbs from mid-October through November and allow leaves to yellow completely.
Prairie-Style Pollinator Patch
Echinacea with rudbeckia (Rudbeckia fulgida), liatris (Liatris spicata), and yarrow. These tolerate heat spells and lean soil, producing sturdy stems and long bloom.
Dry-Garden Dream Team
Lavender with ornamental salvia (Salvia), catmint, gaura (Oenothera lindheimeri), and penstemon. Sharp drainage and full sun are non-negotiable. I do not interplant with hydrangeas or astilbe.
The Sunflower Skirt
Sunflowers (Helianthus annuus) edged with nasturtium (Tropaeolum), calendula, cornflower (Centaurea cyanus), and Ammi majus. I maintain a buffer of eighteen to twenty-four inches around sunflower trunks before tucking in companions.
Cool-Season Cut Bed
Ranunculus (Ranunculus asiaticus), anemone (Anemone coronaria), stock (Matthiola incana), larkspur (Consolida ajacis), and sweet peas (Lathyrus odoratus). Zone 6 springs favor these. I pre-sprout corms, plant under cover in mid- to late March, and trellis sweet peas along one edge. Once heat builds, I pivot to summer annuals.
Shade-Leaning Cuts That Earn Their Keep
Hydrangea (macrophylla or paniculata), astilbe, heuchera, and Japanese anemone (Anemone hupehensis). Even moisture and partial shade are key. I do not force dry-garden species into this guild.
Everlasting Trio
Strawflower (Helichrysum bracteatum), gomphrena (Gomphrena globosa), and statice (Limonium sinuatum). These excel fresh and dried. Lean soil keeps stems strong.
Late-Season Color Block
Asters with rudbeckia and sedum (Hylotelephium). I pinch asters in June for bushiness and leave sedum for structure and fall nectar.
Cottage Spires with Classic Romance
Delphinium (Delphinium elatum), foxglove (Digitalis purpurea), campanula, and roses. I stake well, protect from wind, and allow airflow.
Pairs I Skip (and Why)
Sunflowers suffocating seedlings. Heavy shade and allelopathy can suppress neighbors. I keep a clear ring around trunks.
Bearded iris buried by mulch. Rhizomes must see sun and air to avoid rot.
Roses crammed with spreaders at the crown. Humidity and crowding invite black spot and mildew.
Cool-season flowers held into July beds. Ranunculus, Anemone, stock, larkspur, and sweet peas prefer spring.
Lavender beside hydrangea. Their moisture needs conflict.
Mildew-prone plants packed tight in August humidity. Zinnias, monarda, phlox, and asters need generous spacing and morning irrigation.
My Zone 6 Planting Calendar (At a Glance)
Very early spring (late February–March): Start sweet peas indoors; pre-sprout ranunculus and anemone; direct-sow larkspur, cornflower, calendula as soon as the soil is workable. Transplant stock and snapdragons under cover by late March or early April.
April: Succession sow cool flowers—stock, larkspur, cornflower, nigella, and calendula. Harden off early perennials.
After last frost (mid- to late May): Plant dahlias; set or sow zinnias, cosmos, sunflowers, marigolds, celosia, gomphrena, and basil. Plant lisianthus late May into early June.
June–August: Succession zinnias, cosmos, and sunflowers every two to three weeks until mid-July. Shear sweet alyssum to refresh, and stake or net tall growers.
September–October: Plant or divide perennials (peonies in September–October; bearded iris in July–August; asters, sedum, and echinacea in May–June). Plant bulbs—daffodils from mid-October to November; tulips from mid- to late October. Fall-sow larkspur for spring.
After frost: Lift and store dahlia tubers at forty to fifty degrees Fahrenheit; mulch crowns where needed.
