SowClock

Sowing indoors vs sowing direct

Some seeds want a cosy head start on a windowsill, others prefer to go straight into the soil. Here is how to tell them apart.

Last updated · Sources checked on

Why start seeds indoors?

What the sources say

Many long-season vegetables must be started indoors in early spring so that they have time to ripen before frost. Check the days to harvest on the seed packet to be sure your choices will ripen in time.

(source: University of Minnesota Extension)

What the sources say

Crops such as tomatoes, peppers, aubergines, onions, leeks, celery and parsley are best started from seed indoors and set out as transplants. Tomatoes, for example, take 6 to 8 weeks from sowing to transplanting.

(source: UNH Extension)

Why sow direct?

What the sources say

Vine crops (cucumbers, squash, melons) have roots that are extremely intolerant of disturbance and perform best from direct seeding; if you use transplants, choose small young plants not more than 2 to 3 weeks from seeding. Soil temperature is one of the best guides to spring planting time.

(source: CSU Extension)

What the sources say

Dill and coriander (cilantro) have a taproot and are difficult to transplant: sow them where they will grow.

(source: Illinois Extension, dill; Illinois Extension, cilantro)

In the SowClock calendar

Our explanation

  • Indoors, then planted out: Tomato, Sweet pepper and chilli, Aubergine (eggplant), Kale, Cabbage, Broccoli, Cauliflower, Brussels sprouts, Onion (from seed), Leek, Basil and Parsley.
  • Either way: Cucumber, Courgette (zucchini) and summer squash, Winter squash, Pumpkin, Melon (cantaloupe), Lettuce, Kohlrabi and Swiss chard.
  • Straight into the ground: Sweet corn, Green beans (snap beans), Peas, Spinach, Carrot, Beetroot, Radish, Coriander (cilantro) and Dill.

Potatoes are planted as seed potatoes.

A few tips for indoor sowing

What the sources say

  • A windowsill is often the coldest place in the house at night and the hottest by day; seedlings there tend to grow tall and thin.
  • Seedlings need 12 to 16 hours of light a day, with some darkness at night; lights should hang close above them.
  • Harden plants off before planting out: two weeks before, put them outside for a few hours in the shade and increase the time each day.
(source: University of Minnesota Extension)

What the sources say

Hardening off takes 2 to 3 weeks; it is essential for tender plants such as tomatoes, basil, peppers and French beans.

(source: RHS)

Good to know: the limits

These are general rules. Seed packets often give advice for a specific variety: when they differ, follow the packet for timings and SowClock for the frost dates.

A friendly guide, not a guarantee. Frost dates are averages of past weather, not forecasts: a frost can come later than the average in any year. Crop timings are general rules from university extension services; your soil, microclimate, variety and the weather on the day matter too. Check your local forecast before planting out tender plants.

Sources

Sources checked on 1 November 2026.