When Should You Start Feeding Seedlings? A Beginner's Guide

One of the most common mistakes with seedlings is starting to fertilise too early. A newly germinated seed contains everything it needs to get started — its entire food supply is stored in the seed itself. The seedling does not need, and cannot handle, additional fertiliser for the first weeks of its life. Knowing when to start, what to use and how much to apply is crucial for raising strong, healthy young plants.

The First Weeks: No Feeding Needed

From germination until the first true leaves appear, seedlings are living off the reserves in the seed and the nutrients in the seed compost. Standard seed compost is deliberately low in nutrients to avoid burning the delicate developing root system. Do not add fertiliser at this stage. Focus instead on providing warmth, adequate light and careful watering — the biggest threats to seedlings are damping off (from overwatering) and stretching (from insufficient light), not nutrient deficiency.

When to Start Feeding

The right time to introduce feeding is when the seedling has developed its second set of true leaves and is actively growing. This typically occurs two to four weeks after germination depending on the species and conditions. At this stage the seed's reserves are depleted and the small volume of seed compost may also be running low. A very dilute liquid feed every one to two weeks will support the transition into active growth.

What to Feed Seedlings

The most important word when it comes to seedling feeding is dilute. Even products described as gentle can burn seedling roots at full recommended concentration. Start at one quarter to one half the normal recommended dose and increase gradually as the plant grows. The safest and most forgiving options are:

• Diluted seaweed extract: very gentle, rich in trace elements, stimulates root development — ideal as a first feed
• Diluted balanced liquid fertiliser: at 25–50% recommended concentration; gives balanced nutrition as plants grow
• Comfrey or nettle tea, very diluted: natural, organic, gentle at the right concentration

Avoid applying granular fertilisers to seedling compost — they can sit against roots and cause burning, and dosing them accurately for small volumes of compost is very difficult.

Potting On and Feeding

Each time you pot a seedling on into a larger container with fresh potting compost, the fresh compost provides a new nutrient supply. You can usually take a break from liquid feeding for two to three weeks after potting on, then resume as the plant fills the new pot and begins using the available nutrients. By the time plants are large enough to transplant outdoors, they can handle full-strength feeds and normal adult feeding schedules.