Quick Answer
In Somerville (Zone 6b, last frost roughly April 27 - May 5), start onions and leeks January 17-31, celery and parsley February 1-15, peppers and eggplant February 28 - March 14, tomatoes March 21 - April 4, and basil and most fast-growing summer annuals April 4-11. A south-facing triple-decker window plus a $40 shop light gives you enough light for 12-15 healthy seedling cells. Plant after the soil hits 55 degrees F and frost risk has passed — usually the second weekend in May.
Why Somerville Specifically
Somerville is dense Zone 6b — last frost around April 27 to May 5, first frost around October 15-20, growing season around 165 days. Triple-deckers offer something most urban gardens don't: south- and west-facing windows two to three stories up, with good winter light angle and no first-floor shading from neighbors' fences. If you're in a Davis Square three-decker with a clear south exposure, you've got better seed-starting light than a Newton ranch.
This schedule is dialed for that setup. Adjust later by a week if you're a North End basement, earlier by a week if you've got Powderhouse Hill rooftop access.
The Schedule
January 17-31: Onions and Leeks
Onions from seed take 8-10 weeks before they can go out. Leeks the same. Both want to plant out in mid-to-late April when the soil is workable and the days are 12+ hours.
- Sow: half-inch deep in 4" pots, 8-12 seeds per pot. Trim tops to 3" when they're 6" tall — keeps energy in the root.
- Light: 14-16 hours under shop lights, or a south window with a strong reflector.
- Plant out: April 18-25, after a week of hardening off.
Best varieties for a Somerville garden bed: 'Patterson' (long-day yellow storage onion), 'Red Wing' (red storage), 'Lancelot' (leek).
February 1-15: Celery, Parsley, Lavender
Celery is the slow one — 10-12 weeks to transplant. Parsley wants 8-10 weeks. Lavender needs cold stratification (2 weeks in the fridge) before sowing.
- Sow: surface-press celery and parsley seeds (they need light to germinate); cover with vermiculite. Lavender 1/4" deep.
- Watch: germination is uneven — celery can take 14-21 days. Don't give up.
- Plant out: mid-May for celery and parsley; lavender after May 15.
February 28 - March 14: Peppers, Eggplant, Tomatillos
These are the heat lovers. They need 8-10 weeks to size up before going outside, and they hate cold soil — so they don't go out until late May or even early June in Somerville.
- Sow: 1/4" deep, bottom heat (a heating mat at 75-80 F triples germination rate).
- Pot up: at the 4-leaf stage, into 4" pots.
- Plant out: May 25 - June 5 once nighttime lows are reliably above 50 F.
March 21 - April 4: Tomatoes
The crown jewel of the indoor schedule. Sow too early and you've got leggy plants by mid-April; sow too late and your first ripe fruit slides into August.
- Sow: 1/4" deep, bottom heat at 75 F until germination, then drop to room temp.
- Pot up twice: from cell to 3" pot at week 2-3, then to 4" pot at week 4-5. Bury the stem each time — adventitious roots form along the buried stem.
- Plant out: May 15-25 in Somerville, after at least 5 nights above 50 F.
What You Need
- One $40 shop-light fixture with 5000K LED tubes (cheap and excellent)
- A south or west window that gets 4+ hours of direct winter sun (most Somerville triple-deckers have one)
- Seed-starting mix (NOT garden soil — sterile and light)
- 6-cell trays with bottom-watering tray
- A heating mat (under $30 for the small ones — pays for itself on peppers and tomatoes alone)
- A small fan on a timer for 30 min twice a day (prevents damping off, strengthens stems)
For seed-starting medium and amendments, browse the full Ottr catalog. For Somerville-specific delivery scheduling on bulk loam and compost when it's time to plant out, the Somerville landscape supply collection has the routing.
Hardening Off (the Step Most Beginners Skip)
7-10 days before plant-out, start moving seedlings outside for increasing daily exposure:
- Day 1: 1 hour, shaded
- Day 3: 3 hours, partial sun
- Day 5: 5 hours, full sun
- Day 7: 8 hours
- Day 9: leave out overnight (if night temps are above 50 F for tomatoes/peppers, above 40 F for everything else)
Skip hardening off and your seedlings sunburn within a day. The transition from a 5,000-lumen shop light to a 100,000-lux June afternoon is brutal.
Where the Plants Go After
When transplant time arrives, see 5 Raised Bed Layouts That Maximize a Small Somerville Yard for layout, and How to Layer a Somerville Raised Bed: Loam, Compost, and Mulch in the Right Order for the bed prep. For the broader plan that includes which beds the seedlings fill, see How to Sketch a Garden Plan in a January Notebook.
For neighboring vegetable timing, 5 Vegetables to Start Indoors in Mid-January for Plymouth County Gardens covers South Shore varieties on a similar Zone 6b schedule.
Zone Reality Check
Somerville and most of west Boston are Zone 6b on the USDA Plant Hardiness Zone Map (revised 2023). Coastal pockets — Charlestown waterfront, parts of East Boston — pull into 7a. Cold microclimates — bottom of Powderhouse Hill, Inner Belt low spots — can act like 6a. For zone-reading details, see How to Read the USDA Hardiness Zone Map for Roslindale and West Boston Neighborhoods.
For region-specific vegetable variety recommendations, the UMass Extension Vegetable Program has the most authoritative MA-tested cultivar list.
