Pre-sowing: get started

Pre-sowing (raising seedlings) is one of the easiest ways to get a great start to the season – whether you grow vegetables, herbs, or flowers 🌱✨. When you sow indoors first, you typically get stronger plants, more uniform growth, and often an earlier harvest or flowering.

In this guide, you’ll get a practical walkthrough of the whole process: what is suitable for pre-sowing, how to succeed with seed trays and a mini greenhouse (seed trays with a lid), and when heat and grow lights actually make a difference – without it becoming technical or complicated.

🌿 What is pre-sowing?

Pre-sowing means that you sow seeds indoors (or in a greenhouse) before the soil outside is warm enough. The advantage is that you can control the three things that matter most for success: moisture, temperature, and light.

• Earlier start: you can plant out as soon as the weather allows.
• Stronger plants: seedlings get a calm start without cold and driving rain.
• Less waste: you can sow a little extra and choose the strongest.
• Better use of space: many plants in little space in seed trays.

🗓️ When should you pre-sow?

The best time depends on when the plants can go outside and how fast they grow. A simple rule of thumb is to sow 4–12 weeks before transplanting, depending on the variety.

• Slow/warmth-loving: 10–12 weeks before (e.g., chili/peppers, eggplant, celery).
• Typical greenhouse plants: 6–10 weeks before (e.g., tomato).
• Fast plants: 4–6 weeks before (e.g., lettuce, cabbage, many flowers).
• Very fast: 2–4 weeks before (e.g., cucumber, zucchini – so not too early).

🌱 What can you pre-sow?

You can pre-sow quite a lot. Here are some obvious categories:

Vegetables that often benefit most from pre-sowing

• Tomato, chili and pepper
• Eggplant and celery
• Cabbage (pointed cabbage, kale, broccoli, cauliflower)
• Leeks and onions
• Lettuce and spinach (especially if you want an early start)

Herbs that are good to start in seed trays

• Basil, parsley, chives
• Thyme, oregano and sage
• Coriander (can be a bit slow, but easy to manage indoors)

Flowers that become prettier - and earlier - with pre-sowing

• Marigold, zinnia, cosmos, snapdragon
• Lobelia and other small-seeded flowers (can advantageously be sown in a mini greenhouse)

🧰 Equipment that makes pre-sowing easier

Seed trays - overview and uniform sowing

Seed trays make it easier to keep track of varieties, watering, and space. They provide uniform sowing depth and make it easy to sow many at once without mess.

• Overview: easy to label and keep track of many varieties.
• Space-saving: many plants in little space.
• Even watering: especially if you water gently and consistently.

Mini greenhouse - for stable moisture

A mini greenhouse holds in moisture and makes germination more stable – especially in dry indoor air. It is often the simplest way to get an “easy germination phase” because you don’t have to water all the time.

Seed trays with heat - when temperature is the key

Heat can give faster and more uniform germination if you sow early, or if you have a cool room. Heat helps most before and during germination.

Seed trays with grow lights - when daylight isn’t enough

Grow lights are especially relevant after germination, so the plants become compact and sturdy. If the seedlings become long and thin on the windowsill, more light is almost always the solution.

🪴 Step by step: how to pre-sow

1) Seed compost and sowing depth

• Use fine seed compost or light potting soil without large clumps.
• A good rule is to sow at about 2× the seed’s thickness (very small seeds can lie almost on top).

2) Sow in seed trays and water gently

• Sow 1–2 seeds per cell/pot and cover lightly with soil.
• Water carefully so the seeds aren’t washed away.

3) Germination phase: moisture and calm

• Keep the soil evenly moist – not soaking wet.
• Use a mini greenhouse for stable moisture during germination.

4) After germination: light and air

• Provide plenty of light (window or grow lights).
• Gradually give more air by opening/removing the lid.

💧🔥💡 Moisture, heat and light

Moisture

• Overwatering is the most common mistake – especially under a lid.
• Water a little and often, and let the surface dry slightly between waterings.
• Bottom watering can be smart: the soil absorbs on its own, and the surface stays more undisturbed.

Heat

• Heat makes the biggest difference during germination, especially for warmth-loving seeds.
• Once the plants have sprouted, slightly cooler temperatures can actually result in more compact growth.

Light

• After germination, light is often more important than anything else.
• If the seedlings stretch, provide more light as soon as possible.

🧠 Common mistakes

• Leggy seedlings: more light and preferably a bit cooler after germination.
• Mold on the soil: more air, less moisture, and avoid a constantly wet surface.
• Poor germination: check sowing depth, temperature, and whether the soil dries out.
• Seedlings suddenly die: often too wet and too little air (especially under a lid).

🌤️ Pricking out, potting on and hardening off

• Pricking out: when the plant has true leaves, it can have more space. Lift by the leaves – not by the stem.
• Potting on: when the roots fill the space, give it a larger pot for a stronger root system.
• Hardening off: acclimatize the plants to outdoor conditions over 7–10 days before transplanting.

❓ Frequently asked questions