How to Start Seeds Indoors: A Step-by-Step Guide

Starting seeds indoors gives you a head start on the season, a wider choice of varieties than any garden center, and the satisfaction of growing a plant from the very beginning. It is simpler than it looks.

What you need

• Clean trays, cell packs or small pots with drainage holes
• A light, sterile seed-starting mix (not garden soil)
• A spray bottle or bottom-watering tray
• A sunny south-facing window or, better, an inexpensive LED grow light
• Labels and a waterproof marker

Step 1: Moisten the mix before filling

Seed-starting mix is often dry and hard to wet. Put it in a bucket, add warm water and stir until it feels like a wrung-out sponge. Then fill your cells and press lightly.

Step 2: Sow at the right depth

A good rule of thumb is to plant a seed about two to three times as deep as it is wide. Tiny seeds such as petunias, snapdragons and many herbs need light to germinate and should simply be pressed onto the surface. Always check the packet.

Step 3: Keep them warm and humid

Cover trays with a clear dome or plastic wrap to hold in moisture. Most vegetable seeds germinate fastest at 70–80°F (21–27°C). Peppers and eggplants in particular appreciate a seedling heat mat.

Step 4: Give them strong light immediately

As soon as the first green loops appear, remove the cover and give seedlings bright light. If using a grow light, keep it 2–4 inches above the leaves for 14–16 hours a day. Leggy, pale seedlings are almost always a sign of too little light.

Step 5: Water from below

Set trays in a shallow dish of water for 15–20 minutes, then drain. Bottom watering keeps the surface drier and helps prevent “damping off,” a fungal problem that topples young seedlings. A small fan running gently nearby also helps.

Step 6: Thin and pot up

When seedlings develop their first set of true leaves, snip extras at soil level so one strong plant remains per cell. Fast growers such as tomatoes may need moving into a larger pot before going outside.

Step 7: Harden off and transplant

Before planting outside, seedlings need about a week of gradual exposure to sun and wind. We cover this in detail in our hardening-off guide.

Ready to try? Peppers, tomatoes and many herb seeds are perfect first projects.