What to Plant in March: First Outdoor Sowings and the Indoor Seeds That Need 6 Weeks of Warmth
March is the hinge month of the gardening year. Winter has not fully let go, but the season’s first real push has already begun — and whether that means indoor seed-starting under grow lights or direct sowing cool-season crops in a raised bed depends entirely on where you live. From Zone 3 to Zone 10, March asks something different of every gardener. But there is a common thread: the decisions you make now — what you start, what you plant, and what you prune — will shape your garden’s productivity for the entire season ahead.
Bare-root season is closing fast. Summer bulb pre-orders are urgent. The last winter pruning jobs must be completed before growth breaks. And if you have been putting off starting tomatoes and peppers indoors, the window is narrowing. March rewards the organised gardener — and punishes anyone who waits for “when it feels like spring.”
This guide covers everything you need to do in March, zone by zone, from indoor sowing to outdoor prep. See the Year-Round Planting Guide for how March fits within the full twelve-month planting calendar.
Zone-by-Zone March Planting Table
The most important rule in March: use your USDA hardiness zone, not the date on the calendar. A warm March day can be followed by a hard freeze a week later. Use soil thermometers, not air temperature, for direct sowing decisions.
Seasonal Garden Calendar
Know exactly what to plant, prune and sow — every month of the year.
| Zone | Average Last Frost | March Priority Tasks |
|---|---|---|
| Zone 3–4 | Late May – June | Start tomatoes, peppers, eggplant 6–8 weeks indoors under grow lights. Start leeks, celery, and celeriac. Prune fruit trees while dormant. Order summer bulbs before sell-out. |
| Zone 5–6 | Late April – Mid May | Same as above plus start squash and cucumbers 3–4 weeks before last frost. Direct sow spinach, peas, and radishes outside if soil is above 40°F. Use row cover. Prune roses and ornamental grasses. |
| Zone 7–8 | Mid March – Early April | Direct sow beets, carrots, lettuce, and Swiss chard. Transplant brassica seedlings started in January. Plant onion sets and seed potatoes. Divide perennials. Last bare-root window. |
| Zone 9–10 | January – February | Cool-season crops at end of cycle. Switch to warm-season transplants (tomatoes, peppers, squash). Dahlia rhizomes and canna into ground. Gladiolus succession planting begins. |
Seeds to Start Indoors in March
For most of the country, March is the month to get warm-season crops started under lights. The 6–8 week rule from seed to transplant is not a suggestion — it is how long these plants need to develop the root mass and stem strength to survive outdoor conditions. Starting too early produces leggy, root-bound transplants. Starting too late means a shortened season.
Tomatoes (Zones 3–8)
Start tomatoes 6–8 weeks before your last expected frost date. Use a heat mat set to 75–80°F — tomatoes germinate in 5–10 days at that temperature versus 14–21 days in cold soil. According to Penn State Extension, consistent bottom heat is the single biggest predictor of uniform germination. Once seedlings emerge, move them off the heat mat and under grow lights at 14–16 hours per day. Thin to one seedling per cell.
Peppers and Eggplant (Zones 3–8)
These are the slowest germinators in the warm-season lineup. Start peppers 8–10 weeks before last frost. Eggplant is similar. Both need soil temperatures of 80–85°F to germinate well — a heat mat is not optional here, it is essential. NC State Cooperative Extension notes that pepper germination rates drop sharply below 65°F. Patience is the key variable: do not panic if nothing emerges in the first ten days.
Celery and Celeriac
Start 10–12 weeks before last frost. Surface-sow these seeds — they need light to germinate, so do not cover with soil. Press them firmly onto a moist seed-starting mix and keep at 65–70°F. Germination is slow and uneven. These are low-urgency crops for many gardeners but worth starting in March if you grow them.
Leeks
Leeks need 10–12 weeks from seed to transplant size. Sow into trays at 65–70°F. They can tolerate slightly cooler conditions than tomatoes or peppers, which makes them ideal for a windowsill if grow-light space is limited. According to University of Minnesota Extension, leeks transplanted at pencil thickness establish far more successfully than undersized transplants.
Early Brassicas (Zone 5–6 Primarily)
Cabbage, broccoli, and cauliflower can be started 6–8 weeks before last frost if you did not start them in February. These are cold-tolerant and can be hardened off and transplanted earlier than warm-season crops. Zone 7–8 gardeners should be transplanting brassicas started in January — not starting new ones.
Geraniums and Pelargoniums
These take 12–16 weeks from seed to flowering transplants, which means March is actually the last sensible window for Zone 5–6 gardeners. Surface-sow at 70–75°F. Germination is variable — 10–21 days. Easier to propagate from cuttings taken in late summer, but seed-grown plants are viable if you start on time.
Grow Light Schedule
LED grow lights should run 14–16 hours per day for seedlings. Keep lights 2–4 inches above the tops of the seedlings and raise as they grow to prevent burning. A cheap timer takes the guesswork out of daily on/off cycles. Purdue Cooperative Extension recommends maintaining a dark period of at least 6–8 hours to support healthy cell development.
Direct Sowing in March
Not everything needs to go under grow lights. A handful of crops are genuinely frost-tolerant and perform best when sown directly into the ground as early as the soil can be worked. The rule is soil temperature, not air temperature — invest in a cheap probe thermometer if you do not already have one.
See also our guide to seasonal june planting.
Peas (Zone 5+)
Peas are one of the earliest direct-sow candidates. They germinate at soil temperatures as low as 45°F and tolerate light frosts after germination. Iowa State Extension recommends sowing peas as soon as the soil is workable — typically 4–6 weeks before the last expected frost in Zone 5–6. Sow 1–2 inches deep, 2 inches apart, in double rows 6 inches apart with a trellis between. Sweet peas can be sown directly in Zone 6+ in cardboard tubes to protect the tap root, or started indoors for Zone 3–5.
Spinach, Lettuce, and Arugula
These cold-season greens germinate at 40–50°F and can be sown in Zone 5+ as soon as the soil is thawed and workable. Succession sow every 2–3 weeks through April for a continuous cut-and-come-again harvest. Arugula in particular bolts quickly once temperatures rise, so March and early April are the sweet spot for outdoor growing.
Radishes
Among the fastest crops from seed to harvest — 25–30 days for most varieties. Sow directly in Zone 5+ from mid-March onward, 0.5 inches deep, thinned to 2 inches apart. Radishes double as row markers for slower-germinating crops like carrots.
Soil Temperature Check
Before direct sowing anything, push a soil thermometer 2 inches into the bed. If you do not have a thermometer, the back-of-hand test is unreliable — soil can feel workable long before it reaches the minimum germination temperature. An inexpensive probe thermometer is one of the most useful tools a vegetable gardener can own.
Pruning and Tidy Jobs in March
March pruning is time-sensitive. Do it too early on tender shrubs and a late frost can damage the fresh cuts. Leave it too long and you are cutting into active growth, wasting the plant’s energy budget. The general rule: prune when you can see the buds swelling but before they break into leaf.
Ornamental Grasses
Cut back all deciduous ornamental grasses — miscanthus, pennisetum, panicum — to 3–4 inches above the crown before new growth emerges. Do not cut back too hard if you can already see the green bases of new shoots. Tie the old foliage into a bundle first for a clean cut. Evergreen grasses such as carex and festuca need only a light comb-through with your fingers, not a hard cut.
Buddleia (Butterfly Bush)
Buddleia blooms on new wood, so a hard cut in early March — reducing stems to 2–3 buds from the main framework — produces the best flowering display. If left unpruned it becomes a leggy, top-heavy shrub with small flower spikes. Do not be afraid to cut hard: it will respond vigorously.
Penstemons
Wait until you can see new shoots emerging at the base before cutting back last year’s stems. This is typically mid-March in Zone 6–7. The old stems provide some frost protection over winter, so premature cutting in a cold March can leave the crown exposed. Once basal growth is clearly visible, cut back to just above it.
Roses
Hybrid teas and floribundas should be pruned in March when forsythia is in bloom — a reliable phenological cue across most of the US. Make angled cuts 0.25 inches above an outward-facing bud to direct new growth away from the centre. Remove any dead, damaged, or crossing stems first, then reduce the remaining healthy stems by around half to two-thirds. See the rose growing guide for full detail. Climbers and ramblers are a different matter: leave these until after their first flowering flush — pruning in March removes the buds they are about to open.
Deciduous Hedges
March is the last window for tidying deciduous hedges — beech, hornbeam, hawthorn — before nesting season begins. From April onward, cutting hedges risks disturbing nesting birds. A clean tidy-up now prevents the need for intervention during the sensitive nesting months.
Bare-Root Planting: The Closing Window
Bare-root season runs from approximately December through March, and the window is tighter than most gardeners realise. Once buds are visibly swelling and shoots are more than half an inch long, the plant is no longer dormant — and bare-root transplanting at that point causes significant stress and increased failure rates. If you still have bare-root roses, fruit trees, or hedging to plant, March is the last call.
According to NC State Cooperative Extension, bare-root plants establish faster than container-grown equivalents when planted during dormancy, because the root system can begin actively growing into surrounding soil without the establishment phase required after container removal. But that advantage disappears once dormancy breaks.
Bare-Root Planting Checklist for March
- Soak roots in a bucket of water for 1–2 hours before planting
- Dig a hole wide enough to spread roots without bending them — a mound in the centre supports the graft union
- For roses: plant with the bud union 1–2 inches below soil in Zone 3–5; at or just above soil in Zone 6+
- Backfill, firm, and water in well
- Mulch to 3 inches, keeping mulch off the stem
- Bare-root strawberry plants can still go in this month in Zone 5–7
Once buds are actively growing and you have missed the bare-root window, switch to container-grown stock. Container plants can be planted year-round in most zones, though summer heat is harder on establishment than spring or autumn planting. For more detail on the transition from late winter planting into early spring tasks, see the February planting guide.
Summer Bulb Pre-Ordering: Do Not Wait
March feels too early to be thinking about dahlias, gladiolus, and canna — but the reality of the specialist bulb trade is that the best varieties sell out between March and May, not at planting time. By the time you are ready to plant in late May or June, the cultivars you wanted will be gone.
- Dahlias: Dinner-plate varieties and show-quality tubers from specialist growers sell out by April most years. Order in March, store tubers if they arrive early.
- Gladiolus corms: Particularly heirloom and bicolour varieties. Plan a succession: plant every 2 weeks from last frost to 10 weeks before first autumn frost for continuous bloom.
- Begonia tubers: Large-flowered varieties for shade containers are popular — order before stock depletes.
- Canna rhizomes: Widely available but the largest, most vigorous rhizomes go early from specialist suppliers.
If tubers arrive before planting time, store dahlias in a cool, dry, frost-free location (45–50°F). Do not let them freeze, and do not let them dry out completely. A paper bag in an unheated basement works well.
You might also find seasonal january planting helpful here.
Lawn Care in March
The lawn needs careful handling in March. Grass that has been dormant over winter is fragile, and working on it while the soil is waterlogged or frost-heaved can cause compaction and damage the crown. Patience here pays off — wait for genuinely dry conditions.
First Mow of the Year
Wait until the grass is actively growing — you can tell because you will be able to see new green tips emerging — and until the soil is dry enough that walking on it leaves no footprints. Set the blade high for the first cut: 3.5 inches. The one-third rule applies always: never remove more than one-third of the grass blade in a single mow. Cutting wet, dormant grass scalps it and leaves entry points for disease.
Moss Control
Do not scarify until the grass is actively growing with sufficient vigour to recover — usually April in most zones. March moss treatments (iron sulphate) are fine, but follow up by raking out the blackened moss and overseeding any bare patches once soil temperatures reach 50°F. According to University of Minnesota Extension, overseeding into cold soil produces poor germination and patchy results.
Spring Fertiliser
Do not apply spring fertiliser in early March when cold snaps are still possible — pushing soft growth into a frost night causes significant damage. Wait until growth is steady and consistent, typically late March in Zone 6–7. A slow-release granular fertiliser is safer than a fast-acting liquid feed in the unpredictable conditions of early spring.
Perennial Division in March
Divide overgrown perennial clumps before growth gets too large to handle easily. The standard advice — divide when a clump shows a dead centre, reduced flowering, or simply looks congested — holds. In March you are dividing before leaves fully emerge, which makes it easier to see the crown structure and less stressful for the plant.
Priority candidates for March division:
- Hostas: Divide as the noses (shoots) are just emerging. They recover fast at this stage.
- Daylilies: Can be divided throughout spring but March gives them the longest growing season to re-establish before summer heat.
- Asters: Divide and replant only the outer sections — the vigorous new growth on the edges — and discard the woody centre.
- Ornamental grasses: After cutting back (see above), large clumps can be divided with a sharp spade or saw. Replant at the same depth and water in thoroughly.
Replant divisions immediately — do not let the roots dry out. Water in well and mulch lightly. Divided plants may look underwhelming for the first season but will establish strongly and reward with better flowering the following year.
For everything coming next in the season, see What to Plant in May. And for the full month-by-month overview, return to the Year-Round Planting Guide.
For background on spring planting tasks across the wider garden, the What to Plant in Spring guide covers the key decisions from late March through May. If bare-root roses are on your March list, the rose growing guide covers planting depth, pruning, and establishment in detail.
Check your frost dates with our free Frost Date Calculator to get personalized results for your garden.
Frequently Asked Questions
What can you plant in March?
In Zone 5+, you can direct sow peas, spinach, lettuce, arugula, and radishes outdoors once soil temperatures reach 40°F. Indoors, March is the key month for starting tomatoes, peppers, eggplant, leeks, celery, and celeriac under grow lights. Zone 7–8 gardeners can also direct sow beets, carrots, and Swiss chard, and transplant brassicas started in January.
Is it too early to plant flowers in March?
For most flowering annuals and tender perennials, yes — March is too early to plant outdoors in Zone 5–7. But it is the right time to start many from seed indoors: geraniums and pelargoniums need 12–16 weeks, so a March start is ideal for a June garden. Hardy annuals like sweet peas can be direct sown in Zone 6+ in March. Wait until after last frost for dahlias, begonias, and other tender flowers.
What vegetables can I plant in March?
Outdoors in Zone 5+: peas, spinach, lettuce, arugula, radishes, and (in Zone 7–8) beets, carrots, Swiss chard, onion sets, and seed potatoes. Indoors for later transplanting: tomatoes, peppers, eggplant, squash (Zone 5–6), leeks, and celery. Zone 9–10 gardeners are transitioning from cool-season crops to warm-season transplants.
When should I start tomatoes in March?
Start tomatoes 6–8 weeks before your expected last frost date. If your last frost is May 15 (typical for Zone 6), that means starting around March 20–April 1. Use a heat mat at 75–80°F and grow lights at 14–16 hours per day. Do not start tomatoes more than 8 weeks early — overgrown, root-bound transplants establish poorly outdoors.
Sources
- NC State Cooperative Extension — bare-root planting and tomato transplanting guidance
- Penn State Extension — seed germination temperatures and heat mat use
- Iowa State Extension — pea direct sowing and bare-root strawberries
- University of Minnesota Extension — lawn overseeding and leek transplanting
- Purdue Cooperative Extension — grow light schedules and seedling development
