Sowing seeds now? Do any one of these 8 things and it will probably go wrong

It’s tempting to bring out the same seed packets year after year, but seeds become unviable over time and some species need to be sown fresh in order to get good germination rates. Check the sow by date on the packet and be aware that out-of-date seed packets are more likely to have lower germination rates. Always buy new packets of seed for plants like strawflower (Xerochrysum bracteatum), Anthriscus sylvestris ‘Ravenswing’, parsley and parsnips. If you want to use old seed, but you’re not sure whether it will germinate, you can test its viability before sowing. And, if you do keep seeds from previous years, make sure you store them in a moisture-free container in a cool, dark place.

2. Sowing at the wrong depth

Many seeds need to be covered with a fine layer of compost before they can germinate. But if you sow seeds too deeply, they risk running out of energy before their shoots reach the surface. As a general rule, the larger the seed, the greater the sowing depth. Most seeds need to be covered with approximately their own depth of compost. On the other hand, some seeds, such as poppies (Papaver) and snapdragons (Antirrhinum), require some light to germinate, so it’s important to read the information on the packet to check how deep to sow seeds.

3. Sowing too densely

It might seem sensible to sow as many seeds as possible for the best chance of germination, but this risks producing overcrowded seedlings that need to compete for water, light and nutrients. Sowing too densely also means you’ll need to thin the seedlings, which wastes time and seed, and can damage roots. Most small seeds should be sown thinly. If seeds are too tiny to handle individually, sow a pinch or moisten the end of toothpick with tap water and use it to pick up the seeds. For larger seeds, check the spacing instructions on the packet.

4. Seedlings damping off

Damping off is a fungal disease that can kill seedlings, sometimes causing whole trays of seedings to die. Seedlings are less likely to have issues with damping off if they’re watered with tap water rather than rainwater, which might contain pathogens that could cause damping off. It’s also important to clean pots and trays thoroughly before sowing seed and to use good quality, peat-free compost. Overcrowding and moist, humid conditions make damping off more likely, so ensure that seed is sown thinly and that there’s good air circulation around your seedlings.

5. Too much or too little water

Most seedlings need watering every day or every other day depending on the type of plant, compost and pot. The compost should be kept moist but not saturated. When seedlings begin to wilt, many gardeners assume they need to be watered. But it’s easy to overwater plants, especially when they’re growing in pots in the house. Check the hydration of your seedlings by pushing your finger about an inch down into the compost to see if it’s moist. Sometimes the weigh of the pot can also help you decide whether or not to water. As seedlings grow larger, they’ll need more water.

6. Temperature too cold

All seeds have an optimum temperature range for best germination rates. Some seeds require higher temperatures than others in order to germinate, and these seeds can benefit from being placed in a heated propagator. Check on the back of the seed packet to find out what temperature your seeds require for germination. For seeds sown outdoors in situ, especially in early spring, make sure the soil has reached sufficient temperatures for good germination, usually above 7°C. Otherwise, seeds are likely to sit in the ground, and they may rot before they are able to germinate.

7. Too little light

Growing seedlings indoors helps protect them from cold temperatures, but can create other problems, such as leggy growth through a lack of sufficient light. When seedlings don’t get enough light, they grow upwards more quickly to try and find a brighter spot. This causes etiolated growth and weak plants. If you don’t have good light levels in your house, remove seedlings from heated propagator as soon as they have germinated and plant them a little more deeply when you prick them out. If these methods fail to work, using grow lamps should help increase light levels and lead to stronger growth.

8. Seeds not hardened off

Once your seedlings are ready to transplant into the garden, it’s essential to get them used to outdoor temperatures by hardening them off. This involves putting trays of plants outside during the day and bringing them in at night for a couple of weeks until they’re used to cooler temperatures. Then they can be transplanted into their final positions, and they should grow strongly throughout the season.