Monthly Companion Planting Calendar: What to Plant When

You know which plants help each other (tomato + basil + marigold, carrot + onion, brassicas + dill). What you actually need is a calendar that tells you, month by month, when to start the seeds, when to transplant out, when to direct-sow, and which companion combinations belong in the ground together at each point in the season. That's what this article is.

It's organised the way you'll actually use it: a quick reference table for USDA zones 5–8, then a month-by-month walkthrough from January through December, with the companion combinations that fit each window. Adjust by zone — every guidance below is zone 6 baseline; zone 5 shifts 2–3 weeks later, zone 7 shifts 1–2 weeks earlier, zone 8 shifts 3–4 weeks earlier. Soil temperature is more reliable than calendar date, so we've included the germination thresholds that actually matter.

How to Translate "Month X" to Your Actual Garden

Two numbers run the calendar: your average last spring frost date and your average first fall frost date. Look them up by zip code through the Farmers' Almanac planting calendar or your nearest extension service. NC State Extension notes that "average" means a 50% chance of frost on or after that date — so add a 1–2 week safety buffer for tender transplants like tomatoes.

The second number worth knowing is soil temperature. Oregon State Extension publishes the canonical germination threshold table: peas, lettuce, spinach germinate at 40°F (4°C); carrots and beets need 50°F (10°C); beans and corn want 60°F (16°C); tomatoes, peppers, basil, and squash need 70°F+ (21°C+). Buy an $8 soil thermometer, push it 3 inches (7.5 cm) into the bed, wait two minutes, read the result. Anything you plant before the soil hits its threshold either rots or stalls.

Source: Park Seed — First and Last Frost Dates by USDA Zone and Bonnie Plants — Frost Dates.

Every "Month X" reference below is zone 6 baseline. Zone 5: shift everything 2–3 weeks later. Zone 7: 1–2 weeks earlier. Zone 8: 3–4 weeks earlier. Before any planting, our complete companion planting chart covers which combinations actually work — this article tells you when to plant them.

January — Plan, Order, Stratify

Outside, nothing is happening. Inside, this is when the season is decided. Order seeds early (good cultivars sell out by March). Sketch the layout — which beds get the spring greens, which get the summer heavy hitters, which get the fall brassicas. This is also the only month to cold-stratify certain perennial seeds (like sea kale or some native flowers) by sealing them in a damp paper towel in the fridge for 30–60 days.

Indoor seed-starting begins for slow growers. Onions and leeks (12–14 weeks before last frost) and celery (10–12 weeks) go under lights now. Cornell Cooperative Extension's planting dates guide confirms onions are the earliest practical seed-start for cool-temperate gardeners. Use a heat mat (75°F / 24°C soil) and grow lights on a 14–16 hour timer.

February — Brassicas and Peppers Indoors

Late February is the start gun for indoor seed-starting in zone 6. Brassicas (broccoli, cabbage, cauliflower, kale) and peppers go in trays now — 8–10 weeks before last frost. Eggplant follows the same window. Use a heat mat for peppers and eggplant; brassicas germinate fine at room temperature.

Outside, if the soil thermometer reads above 40°F (4°C), garlic cloves planted last October are pushing green tips. Top-dress with compost. Order onion sets if you didn't seed-start in January.

Companion planning note: When you start tomato seeds in February or March, also start basil. Both transplant out at the same time, and basil grown alongside tomato from day one performs better than basil dropped in next to a mature tomato in June. Homestead and Chill's tomato companion guide has the full pairing protocol.

March — Peas, Spinach, Radishes; Tomatoes Indoors

March is the first real outdoor month for cool-temperate gardeners. The trigger isn't the date — it's soil temperature at 40°F (4°C) and rising, plus a soil that crumbles in your hand instead of clumping into mud. Cornell's first planting dates guide calls this "as soon as soil can be worked," typically 4–6 weeks before last frost.

Direct-sow outdoors: peas (sugar snap, snow, shelling), spinach, lettuce, arugula, radishes, kale seed, mâche, fava beans (overwintered), parsley. Penn State Extension's seed planting guide PDF covers spacing for all of them.

Indoor starts: tomato, pepper (if not already), basil, eggplant, herbs (sage, oregano, thyme starts).

Spring companion combinations to plant together:

Source: Gardenary — 10 Easy Companion Planting Combos and Penn State Extension.

Our spring companion planting deep dive covers the full cool-season pairing logic. Start succession sowing now too — a small lettuce planting every 2 weeks beats one big planting that bolts all at once in June.

April — Hardening Off, Carrots and Beets

Indoor seedlings need hardening off — 7–14 days of gradual outdoor exposure before transplanting. Start with 1 hour of dappled shade and build up. Skip this step and your tomatoes sunburn the day after you plant them out.

Direct-sow outdoors: more peas (extend the harvest), carrots (now that soil is 50°F / 10°C), beets, chard, lettuce, kale, broccoli rabe, more radishes, turnips, parsnips, dill (self-seeding around the future tomato bed).

Transplant out (after last frost in zone 7+): hardened-off brassica starts, lettuce starts, parsley, hardy herbs.

Indoor: cucumber, melon, summer squash, winter squash (3–4 weeks before last frost — they hate root disturbance, so direct-sow if you prefer).

This is also the month to plan succession plantings of beans for June, July, and August. Mark dates on the calendar now, not later.

May — The Big Plant-Out

May is the high-stakes month. Last frost passes (around May 1 in zone 6, May 15 in zone 5) and the warm-season crops finally go in the ground. Audrey's Little Farm runs a useful primer on why planting too early — typically 1–2 weeks before last frost — kills more transplants than any pest. Soil temperature still drives the decision: tomatoes and peppers want 65°F+ (18°C+) at planting depth, ideally 70°F (21°C).

Transplant out (after last frost): tomatoes + basil + marigolds (the canonical trio); peppers + basil; eggplant; cucumbers (or direct-sow); melons; squash; pumpkins.

Direct-sow: bush beans, pole beans (with corn for Three Sisters), summer squash, sweet corn, cucumbers, sunflowers (companion + late pollinator support), nasturtiums.

This is the month for the iconic summer companion combinations:

Source: Garden Betty — Three Sisters Garden Guide and Penn State Master Gardener York County (PDF above).

June — Mulch, Train, Succession Sow

By June, the spring crops are peaking and the summer crops are settling in. Three jobs this month: mulch deeply (3–4 inches / 7.5–10 cm of straw or wood chips around tomatoes, peppers, squash to conserve moisture and suppress weeds); train climbers (tomatoes to single or dual stems; pole beans up the trellis; cucumbers along their support); and continue succession sowing.

Succession sow (every 2–3 weeks): bush beans, lettuce (heat-tolerant cultivars only), radishes, carrots, more dill. Illinois Extension's succession planting chart (PDF) spells out the windows for every crop.

Harvest: overwintered garlic (when half the leaves yellow), peas (before they get starchy), spinach (before bolt), strawberries, lettuce, radishes, last of the cool-season greens.

This is also when fall brassica planning begins. Order seed for fall broccoli, cabbage, kale, and Brussels sprouts — they'll need to start indoors in early-to-mid July.

July — Peak Production, Fall Brassica Starts

July is the cruise month. Most of the garden is producing on its own. The two real tasks: start fall brassicas indoors (8–10 weeks before first fall frost — for zone 6 with Oct 15 first frost, that's mid-July) and direct-sow fall carrots, beets, and turnips mid-month.

Direct-sow: bush beans (last reliable round), summer lettuce (heat-tolerant), more dill, fall carrots, fall beets, turnips, fall peas (zone 7+).

Transplant out (early): Brussels sprouts seedlings if started in May (need 100+ days to mature before first frost).

Harvest: tomatoes (just starting), peppers, summer squash, cucumbers, beans, basil, blueberries, raspberries, currants.

If your tomatoes are showing yellow lower leaves, that's not a calendar problem — it's typically watering or nutrient. Consult our soil health guide on what's likely depleted by mid-summer.

August — Plant Fall Brassicas, Harvest Peak

August is when the fall companion garden goes in. Transplant your indoor-started brassicas (broccoli, cabbage, cauliflower, kale, Brussels sprouts) into beds where the spring greens or peas finished. Pair them with dill (attracts parasitic wasps that target cabbageworms) and sweet alyssum (brings hoverflies). High Mowing Seeds' fall brassica guide covers the timing in detail — for zone 6, August 1–15 is the transplant window.

Direct-sow: spinach, lettuce, arugula, mâche, radishes, kohlrabi, fall turnips, garlic-precursor cover crops.

Harvest: peak tomato, pepper, eggplant, beans, summer squash, melons, sweet corn (1 ear per stalk for sweet corn), basil for pesto, cucumbers, blueberries, blackberries.

Companion combinations to install for fall:

Source: High Mowing Seeds — Fall Planting Guide and UC Master Gardeners Santa Clara — Vegetable Planting Chart.

September — Garlic, Cover Crops, Last Spinach

September is transition. The fall brassicas are bulking up. Tomato production is winding down (frost preparation begins). Two important seeding jobs: plant garlic (mid-September in zone 5, late September in zone 6, October in zone 7+ — cloves need 6–8 weeks of root growth before hard freeze) and sow cover crops on any beds that won't be growing through winter.

Direct-sow cover crops: winter rye (zones 3–9), crimson clover (zones 6–9), hairy vetch (zones 4–9), white clover, oats (will winterkill — that's fine), buckwheat (only if 6 weeks before frost). USDA NRCS's cool-season cover crop research (PDF) covers the planting-date trade-offs for each.

Direct-sow vegetables: last spinach (overwinters), arugula, mâche, lamb's lettuce, last radishes (zones 7+).

Harvest: winter squash (when stems are dry and rinds are hard), pumpkins, last tomatoes, peppers, sweet potatoes, fall lettuce, kale, broccoli, dry beans.

October — Garlic, First Frost, Mulch

The first fall frost lands around October 15 in zone 6, October 30 in zone 7. Cover or harvest tender crops before frost. Brassicas, kale, chard, spinach, and root vegetables all tolerate frost and actually improve in flavour after a cold snap.

Plant garlic (zones 6–7 main window). 4 inches (10 cm) deep, 6 inches (15 cm) apart, pointed end up. Mulch with 4 inches of straw or shredded leaves. Hardneck cultivars for zones 4–7, softneck for zones 7+.

Mulch the food forest and perennial beds. The fall leaf flush is free organic matter — see our sheet mulching guide for converting them into next year's bed.

Harvest: apples, pears, late raspberries, fall brassicas (broccoli heads, cabbage, cauliflower as ready), Brussels sprouts (after frost), kale, chard, fall carrots, beets, parsnips (improved by frost), winter squash storage.

November — Cover, Mulch, Plan

By November, most beds are either covered in mulch, growing cover crops, or holding the last fall brassicas. Wisconsin Extension's monthly gardening guide calls this the "tucking in" month — protect overwintering crops, finish leaf cleanup, and start the next year's planning.

Tasks: top up mulch on garlic beds and overwintering spinach/kale; clean and store tools; review what worked this season; order next year's seeds while inventories are full.

Harvest: Brussels sprouts (best after multiple hard frosts), kale (deepens in flavour), parsnips, fall lettuce under row cover, last carrots before ground freezes.

December — Rest, Read, Plan

Genuine off-season in zones 5–7. The work is mostly indoors: review garden journals, sketch next year's layout, study companion combinations, and rest. In zones 8+, this is a productive month for cool-season crops (lettuce, brassicas, peas, garlic) — adjust the calendar accordingly.

Tasks: finalise seed orders for January delivery; prep indoor seed-starting space (lights, heat mat, trays, soilless mix); inspect and sharpen tools.

Quick-Reference: Companion Combinations by Season

Source: Texas A&M AgriLife — Vegetable Garden Planting Guide (PDF) and OSU Extension Monthly Garden Calendars.

Frequently Asked Questions

What should I plant in my garden right now?

It depends on your USDA zone and the date, but the simple rule is: check soil temperature with an $8 thermometer, then match it to germination thresholds. Soil at 40°F (4°C)? Plant peas, spinach, lettuce, radishes. Soil at 50°F (10°C)? Add carrots, beets, chard. Soil at 60°F (16°C)? Add bush beans, pole beans, corn, squash. Soil at 70°F (21°C)? Plant tomatoes, peppers, basil, eggplant, melons. The calendar dates are guides; soil temperature is the actual signal.

What is the best month to start a garden?

March in zones 6–7, April in zone 5, February in zones 8+. That's when soil first hits 40°F (4°C) and you can direct-sow peas, spinach, and lettuce. If you're starting from scratch, late winter is also when you build the bed (sheet mulching) and order seeds — so the actual "start" is January or February. By March or April, you're planting into a prepared bed.

When should I plant vegetables by month?

Zone 6 baseline: Mar: peas, spinach, lettuce, radishes, parsley. Apr: carrots, beets, chard, brassica transplants, more peas. May: tomatoes, peppers, basil, beans, corn, squash, cucumbers, eggplant. Jun: succession beans and lettuce; mulch heavily. Jul: fall carrots, beets, turnips; start fall brassicas indoors. Aug: transplant fall brassicas; sow fall lettuce, spinach, kale. Sep: garlic, cover crops, last spinach. Oct: garlic, mulching, harvest. Nov–Feb: rest, cover crops, planning. Adjust by zone — earlier in 7–8, later in 4–5.

What are the best planting days?

By soil temperature and weather, not lunar phase. The Old Farmer's Almanac publishes a "best planting days" calendar based on lunar position — that tradition has cultural value but the scientific evidence for moon-phase planting effects is weak. Use it if you enjoy the structure; ignore it without missing anything important. The actual best planting day is one where soil is at the right temperature for the crop, no frost is forecast for the next 7 days, and the soil is workable (crumbles, doesn't clump).

Can I plant vegetables in summer?

Yes — summer is the second main planting window. Direct-sow bush beans, pole beans, summer squash, cucumbers, basil, dill, summer-tolerant lettuce cultivars, fall carrots (mid-July onward), and fall brassica seedlings (start indoors mid-July, transplant August). The trick is avoiding peak heat — sow in the late afternoon or on overcast days, water immediately, and shade tender seedlings if temps exceed 85°F (29°C). Heat-stressed transplants establish poorly.

When should I start seeds indoors?

Count backwards from your last frost date. Onions and leeks: 12–14 weeks before. Brassicas, peppers, and eggplant: 8–10 weeks before. Tomatoes and basil: 6–8 weeks before. Cucumbers, melons, squash: 3–4 weeks before (these dislike root disturbance — many gardeners direct-sow instead). Lettuce, herbs (parsley, cilantro): 4–6 weeks before. Grow a Good Life's seed-starting guide covers the full timing chart.

Should I follow a lunar planting calendar?

Lunar planting (the idea that above-ground crops should be sown during the waxing moon and root crops during the waning moon) is an old practice with weak modern evidence. Some gardeners report success with it; controlled studies show no statistically significant effect. If you want to use it, the framework is published in the Farmers' Almanac. If you prefer evidence-based timing, soil temperature and frost dates will give you the same or better results without the moon-phase tracking.

Resources

• Cornell Cooperative Extension — Planting Dates
• Cornell Cooperative Extension Tompkins — First Planting Dates
• Oregon State Extension — Soil Temperature for Vegetable Seed Germination
• Oregon State Extension — Monthly Garden Calendars
• Penn State Extension — Vegetable Seed Planting Guide (PDF)
• UC Master Gardeners Santa Clara — Vegetable Planting Chart
• UMN Extension — Planting Dates and Distances (PDF)
• Wisconsin Extension Portage — Monthly Gardening Guide
• Illinois Extension — Succession Planting Chart (PDF)
• NC State Extension — Average First and Last Frost Dates
• USDA NRCS — Cool-Season Cover Crop Planting Dates (PDF)
• Texas A&M AgriLife — Vegetable Garden Planting Guide 2025 (PDF)
• Park Seed — First and Last Frost Dates by USDA Zone
• Farmers' Almanac — Planting Calendar by Zip Code
• High Mowing Seeds — Fall Brassica Planting Guide