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March Gardening Guide

Early Spring | The Growing Season Begins

March marks the true beginning of the outdoor growing season for most gardeners. As the soil warms and days lengthen, cool-season crops can go directly into containers while warm-season seedlings continue growing under lights indoors. This is an exciting month of transition from planning to planting!

What to Plant in March by Zone

Zones 3-5

Cold

Start Indoors

  • Tomatoes
  • Peppers (early month)
  • Broccoli
  • Cabbage
  • Cauliflower
  • Herbs

Plant Outdoors

  • Peas (late month with protection)
  • Spinach (late month)
  • Lettuce under cover

Harvest

  • Indoor herbs
  • Microgreens
  • Sprouts

Prime seed starting month! Start tomatoes early month. Begin cold frame plantings late month. Watch for late snow.

Zones 6-7

Moderate

Start Indoors

  • Tomatoes
  • Cucumbers
  • Squash (late month)
  • Basil
  • Melons (late month)

Plant Outdoors

  • Peas
  • Lettuce
  • Spinach
  • Kale
  • Radishes
  • Onion sets
  • Potatoes (Zone 7)

Harvest

  • Overwintered greens
  • Cold frame crops
  • Early radishes

Busy month! Start warm-season crops indoors while direct sowing cool-season crops outside. Begin hardening off early seedlings.

Zones 8-9

Mild

Start Indoors

  • Melons
  • Squash
  • Cucumbers
  • Pumpkins

Plant Outdoors

  • Tomato transplants (late month)
  • Peppers (late month)
  • All cool-season crops
  • Potatoes
  • Beans (late month)

Harvest

  • Lettuce
  • Spinach
  • Peas
  • Radishes
  • Broccoli
  • Herbs

Transition month! Plant warm-season transplants after last frost. Final cool-season plantings before heat arrives. Harvest winter crops.

Zones 10-11

Warm/Tropical

Start Indoors

  • Start fall tomatoes (late month)

Plant Outdoors

  • Tomatoes
  • Peppers
  • Eggplant
  • Squash
  • Cucumbers
  • Beans
  • Corn
  • Melons

Harvest

  • Cool-season crops before bolting
  • Tomatoes
  • Peppers
  • Citrus
  • Herbs

Warm-season planting in full swing! Harvest remaining cool-season crops before they bolt. Watch for increasing pest pressure.

March Maintenance Tasks

Seed Starting

  • Start tomatoes 6-8 weeks before last frost
  • Begin cucumbers, squash, and melons 3-4 weeks before transplanting
  • Pot up February-started seedlings to larger containers
  • Start basil and other warm-season herbs
  • Thin seedlings to strongest plants
  • Increase fertilizing for fast-growing seedlings
  • Adjust grow light height as seedlings grow

Hardening Off

  • Begin hardening off peppers and eggplant started in February
  • Move seedlings outside for increasing periods each day
  • Start in shade, gradually increase sun exposure
  • Reduce watering slightly to toughen plants
  • Watch weather forecasts for cold snaps
  • Protect seedlings from wind during hardening off
  • Stop fertilizing 1 week before transplanting

Container Prep

  • Clean and fill containers with fresh potting mix
  • Pre-warm containers in sunny locations
  • Install drip irrigation or self-watering systems
  • Position containers for optimal sun exposure
  • Add slow-release fertilizer to soil
  • Check drainage holes are clear
  • Set up supports for climbing plants

Direct Sowing

  • Direct sow peas as soon as soil is workable
  • Plant lettuce, spinach, and arugula seeds
  • Sow radishes for quick harvest
  • Plant onion sets and seed potatoes
  • Start succession planting schedule
  • Cover newly sown seeds with row cover for warmth
  • Keep soil consistently moist for germination

March Pest Watch

As temperatures warm, pest pressure increases. Early detection is crucial for preventing infestations. Inspect plants daily, especially new transplants and tender seedlings.

Aphids

New growth on seedlings and transplants

Signs:

Clusters of small soft-bodied insects, sticky honeydew, curled new leaves

Prevention:

Inspect plants daily, avoid over-fertilizing with nitrogen, encourage beneficial insects

Treatment:

Spray off with water, insecticidal soap, neem oil, introduce ladybugs or lacewings

Cutworms

Soil level around transplants

Signs:

Seedlings cut off at soil level overnight, curled gray caterpillars in soil

Prevention:

Use collars around transplant stems (toilet paper tubes), keep area weed-free

Treatment:

Hand-pick at night, Bacillus thuringiensis (Bt), diatomaceous earth around plants

Flea Beetles

Brassicas, eggplant, and leafy greens

Signs:

Tiny holes in leaves (shot-hole damage), small jumping black beetles

Prevention:

Use row cover immediately after planting, interplant with trap crops

Treatment:

Neem oil, diatomaceous earth, sticky traps, spinosad for severe infestations

Slugs & Snails

Young seedlings, especially in wet conditions

Signs:

Irregular holes in leaves, slime trails, damage appears overnight

Prevention:

Water in morning (not evening), remove debris, copper tape around containers

Treatment:

Hand-pick at night, beer traps, iron phosphate bait, diatomaceous earth when dry

Tips for March Success

Know Your Last Frost Date

Your last frost date is the key to March timing. Count backward to know when to start seeds and forward to know when it's safe to transplant. Build in a buffer - nature doesn't follow calendars exactly.

Prepare for Weather Swings

March weather is notoriously unpredictable. Keep row covers, old sheets, and plastic containers ready for frost protection. Have a plan for moving containers to protected areas if needed.

Start Succession Planting

Begin your succession planting habit now. Plant lettuce and radishes every 2 weeks for continuous harvest. Note planting dates in your garden journal to refine your schedule each year.

Prepare Vertical Structures

Install trellises, stakes, and cages before plants need them. Climbing peas should go in as soon as seeds are sown. Tomato and cucumber supports should be ready before transplanting.

March Container Projects

Cool-Season Salad Container

Beginner

Create a complete salad garden in one large container with lettuce, spinach, radishes, and greens.

Supplies Needed:

  • 5+ gallon container
  • Quality potting mix
  • Lettuce and spinach seeds
  • Radish seeds
  • Row cover

Tips:

  • Mix multiple lettuce varieties for color and texture
  • Radishes mark rows and are ready in 25-30 days
  • Use row cover for frost protection and pest exclusion
  • Begin harvesting outer leaves in 3-4 weeks
  • Succession plant every 2 weeks until heat arrives

Pea Tower Container

Beginner

Grow climbing peas vertically in a container with built-in support for space-efficient harvests.

Supplies Needed:

  • 5+ gallon container
  • 6-foot trellis or netting
  • Stakes or frame
  • Pea seeds
  • Inoculant (optional)

Tips:

  • Install support before planting
  • Soak seeds overnight to speed germination
  • Use pea inoculant for better nitrogen fixation
  • Plant 2 inches apart, 1 inch deep
  • Harvest daily once pods form to encourage more production

Tomato Seedling Station

Intermediate

Set up an efficient seed starting station for tomatoes and other warm-season crops.

Supplies Needed:

  • Seed starting trays with cells
  • Heat mat
  • Grow lights
  • Timer
  • Seed starting mix

Tips:

  • Position lights 2-4 inches above seedlings
  • Run lights 14-16 hours daily
  • Heat mat speeds germination significantly
  • Pot up to 4-inch pots when first true leaves appear
  • Begin fertilizing with dilute liquid fertilizer at potting up

Frequently Asked Questions

What vegetables can I plant outside in March?
In most zones, March is perfect for cool-season crops: lettuce, spinach, kale, peas, radishes, arugula, and Asian greens. These tolerate light frost and prefer cooler soil. In zones 8-11, you can also transplant brassicas (broccoli, cabbage, cauliflower) and plant potatoes. Wait until after your last frost for warm-season crops like tomatoes and peppers.
When should I start tomato seeds in March?
For zones 5-7, early to mid-March is ideal for starting tomatoes indoors (6-8 weeks before last frost). Zone 8 gardeners should have already started tomatoes in February. Count backward from your last frost date and add 2 weeks for hardening off. Starting too early creates overgrown, stressed seedlings.
How do I harden off seedlings started in February?
Begin hardening off 7-10 days before transplanting. Week 1: Place seedlings outside in a sheltered, shaded spot for 2-3 hours, then bring inside. Gradually increase outdoor time and sun exposure daily. By week 2, leave them out overnight if temperatures stay above 50°F. Reduce watering slightly to toughen plants before transplanting.
Is it too late to start peppers in March?
In zones 3-6, early March is the last chance to start peppers from seed (they need 8-10 weeks indoors). In warmer zones, you may be better off buying transplants for this year. Peppers need consistent warmth (75-85°F) for germination and grow slowly, so late starts often produce poorly.
What should I do if we get a late frost in March?
Have protection ready! Cover tender plants with row cover, sheets, or plastic containers before sunset (remove in morning). Move container plants against building walls or into garages overnight. Water soil thoroughly before freeze - moist soil holds more heat. Don't remove covers until temperatures rise above freezing.
Can I direct sow seeds in containers in March?
Yes! Cool-season crops like lettuce, spinach, radishes, peas, and arugula can be direct sown in containers once soil temperatures reach 40-50°F. Pre-warm containers in sunny spots before sowing. Cover with row cover for 4-8 degrees of frost protection. Succession plant every 2 weeks for continuous harvest.
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