Tips for Seed Germination

Growing from seed is a satisfying and thrifty way of adding new plants to your garden, but the process can seem intimidating to a beginner. However, guiding a seed toward germination is straightforward if you follow a few basic ideas, and it quickly becomes second nature. Here’s what you need to know.

A seed is made up of two main parts. The inner kernel contains the genetic instruction set needed to grow a specific plant variety, alongside a store of energy to power the seedling’s early growth. This kernel is protected by a tough outer husk which keeps out the elements until conditions are right for growth to begin. Seed germination is simply the moment when the kernel leaves its dormant state, and pushes a shoot out through the husk, to start growing into a seedling.

A healthy seed’s only ambition is to start the germination process, and if you can provide the right conditions, it’ll happen easily. In general, a combination of light, temperature, and moisture that mimics the spring weather is enough to get seed germination going. But within that simple idea there are a few important points to bear in mind to ensure successful germination.

A seed will germinate in any soil, including that taken from your garden. But for best results, always use a good-quality seed compost which will be guaranteed free from disease and pests. And importantly, use fresh compost for each sowing to prevent problems building up through re-use.

Different species of seeds need different light levels to prompt germination, and the main way of satisfying those needs is to sow the seeds at the right depth under the soil to naturally block or limit the light that reaches down.

The seed packet will usually give the correct sowing depth, but a general rule of thumb is to plant a seed three times as deep as it is wide. So, a large bean seed that’s half an inch across should be sown 1.5″ (3.5-4cm) deep, while a tiny carrot or poppy seed should be covered with only a sprinkling of compost.

However, some seeds such as lettuce and begonia need full light to germinate, and these should be sown on the surface. Again, seed packets will give the right instructions, but if a species is one that naturally self-seeds from one year to the next, then surface sowing is the usually right approach.

The majority of seeds need a soil temperature of between 68-78°F (20-25°C) to germinate, although tropical species may need a few degrees more. Using heated mats can help keep the soil temperature in the right range, while covering germination pots with a clear plastic lid can help push temperatures up to germination levels in cooler areas.

Constant moisture is essential for germinating any seed. If the soil dries out completely, the seed will either fail to germinate at all or die shortly afterward. However, be careful not to over-water the compost and leave it waterlogged, which can lead to the seed rotting or being affected by a fungal disease called damping off. And what’s more, soil that’s too wet will deprive the seed of the oxygen it needs to survive, effectively drowning it before it can germinate.

The safest way of striking the right watering balance is to ensure the compost is thoroughly moist but not wet before sowing, and then to spray the surface lightly with a garden mister whenever it starts to look dry, being careful not to soak the compost through.

The length of time each seed variety takes to germinate is given by the ‘days to germinate’ measure, which estimates the time from sowing to the first shoot breaking the surface. It’s important to know roughly how long your seeds should take, so that you can spot a failed germination and re-sow without wasting too much time. However, as a rule of thumb, expect to see germination begin from around three to ten days, although some plants such as parsley and peppers can take several weeks.

For seeds which are particularly slow germinators, the process can often be sped up by soaking the seeds in plain water for six to twelve hours before sowing. This helps to soften the husk and gives germination a head start. However, soaking seeds can increase the risks of rot and fungus, so use the method with care.

Raising a mature plant from seed is a satisfying experience for any gardener, and it’s easier than most people think. For more information on caring for plants at their youngest stages, read our article on how grow lights can help your seeds before and after germination.