Gardeners eager for warmer weather can get a head start on the growing season by sowing seeds indoors now, according to horticultural experts. With spring still weeks away, starting seeds inside offers a way to bridge the gap and ensure a vibrant garden when conditions improve.
Julian Palphramand, head of plants at British Garden Centres, recommends tomatoes as an ideal starting point. “Tomatoes are easy to grow and endlessly rewarding with lots of juicy fruit over the summer,” he said. Seeds should be sown approximately one centimetre deep in seed compost, covered with a clear lid or cling film to maintain humidity, and kept in a warm location – ideally between 18 and 21°C. Seedlings should appear within a week or two.
Outdoor planting of tomato plants should occur once they reach about 20cm in height with sturdy stems, and after all risk of frost has passed, typically in late May or early June. Palphramand advises a gradual “hardening off” process over a couple of weeks to acclimate the plants to cooler outdoor temperatures.
Peppers and chillies too benefit from early indoor sowing, though they require slightly warmer temperatures, between 21 and 25°C. Seeds should be sown on the surface of moist compost and lightly covered. Germination can seize up to three weeks, Palphramand noted.
Aubergines, similar to peppers and chillies, thrive with warmth and indoor care before being transplanted outside. “Think of them as the divas of the vegetable patch,” Palphramand explained, “they love heat, sunshine and a bit of pampering.” Outdoor planting is best done when conditions are consistently warm, with a greenhouse offering an ideal environment, though a sheltered, sunny spot can also work.
Beyond vegetables, flowers can also be started indoors now. Palphramand highlighted sweet peas as a particularly good choice, praising their fragrance and ease of growth. He recommends soaking the seeds overnight to soften their coats before sowing them two to three centimetres deep in individual pots or root trainers, where they should germinate within two weeks. Sweet peas can be planted outside as early as March or April, as they tolerate cooler conditions and even light frost. Pinching out the growing tips encourages bushier growth and more blooms, and the plants will require support from bamboo canes or a trellis.
For quicker results, zinnias are another option, germinating in as little as five days when kept warm at around 20 to 25°C. Cosmos are also suitable for indoor sowing, with seeds sown on the surface of compost and germinating within a week.
Palphramand emphasized the importance of ensuring seedlings are strong enough before transplanting them outdoors. “The biggest mistake many gardeners make is planting out seedlings before they’re strong enough,” he said. He advises looking for sturdy, well-coloured plants with firm growth and several sets of true leaves, and roots beginning to emerge from the drainage holes as a sign of readiness.
“Hardening off” is a crucial step, involving gradually increasing the seedlings’ exposure to outdoor conditions over about two weeks. Transplanting should ideally occur on an overcast day or evening to minimize stress on the young plants. Adequate watering before and after planting, adherence to seed packet spacing recommendations, and protection from the elements, such as with fleece or cloches, will help ensure successful establishment.