Growing from seed is one of the most satisfying and rewarding ways to furnish your garden with new plants, perhaps with a few spares to give away or swap. It’s also inexpensive, so if you don’t succeed at first, it won’t cost an arm and a leg to try again.
Confronted with a fresh packet of seeds, among your first decisions will be where to sow them. Your instinct may be to reach for a seed tray or small pot to start them in. In many cases, this will be the best approach, but not always: you also have the option of sowing them outdoors, where you intend them to grow. This isn’t such a crazy idea - your garden is probably full of plants that have seeded themselves and germinated unaided. Beyond our towns and cities, the countryside is a tapestry of trees, shrubs, wildflowers and food crops that grow happily without ever having been cosseted on a window ledge or in a greenhouse.
Plants have adapted to their environment over millions of years. Some are chancers, opportunists that can grow from seed almost anywhere and alter their growing habits accordingly. Dandelions are a great example, growing tall and lush in damp meadows and almost completely prostrate in gaps in the pavement. Other plants have extremely niche requirements if they are to germinate - for example, exposure to smoke, periods of extreme cold or even a journey through an animal’s digestive system!
When choosing which sowing method to employ, the main deciding factors are how hardy the seeds are, what conditions they need to germinate and the size of the seeds. Take, for example, the tobacco plant, Nicotiana sylvestris. The dust-fine seeds of this Bolivian beauty require heat to germinate, the seedlings won’t survive frost, and they are prone to being eaten by pests, so typically they would need to be sown indoors in the UK. In contrast, common sunflowers (Helianthus annuus) and runner beans have large seeds, distinctive seedlings, and dislike being disturbed, so they are better sown outdoors, albeit when the danger of frost has passed. Somewhere in between, zinnias and cosmos, both half-hardy annuals, must be sown indoors before May, but sowing outdoors in June will often produce bigger, stronger plants, albeit flowering a little later.
Below, I weigh up the pros and cons of sowing indoors or outdoors, which gardeners sometimes refer to as ‘direct sowing’.
Sowing outdoors
I’m starting with direct sowing as I find this is the method most gardeners feel least comfortable with. Why? Because it offers significantly less control and carries a higher risk of failure. However, I would argue that we need to embrace direct sowing more as we attempt to garden more sustainably. Timed correctly, cared for properly and blessed with favourable weather conditions, many flowers and vegetables sown directly in the soil will perform better and mature more quickly than those sown indoors. It’s not right for every type of plant, but it has many advantages:
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Space is plentiful - we generally have much more room to grow things in our gardens than we do on windowsills or in greenhouses and cold frames. Direct sowing opens up more possibilities for gardeners and preserves precious indoor space for those seeds that demand it.
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It's less wasteful - direct sowing harnesses the soil we’ve worked so hard to cultivate, meaning we don’t have to buy expensive compost. Soil contains minerals and microorganisms that promote germination and support the early stages of plant growth … but may also harbour competing weed seeds. Direct sowing also negates the need for plastic pots and trays, which take up space and often can’t be recycled.
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You grow hard and fast - seedlings grown in the soil don’t need to be pricked out and potted on, allowing them to grow unchecked. This benefits plants with long tap roots, like poppies and hollyhocks, which respond negatively to disturbance. Higher light levels and exposure to wind and rain promote the development of strong, stocky seedlings that are more resilient than those grown indoors.
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It's less effort - compared to indoor sowing, direct sowing is a breeze. So long as the soil is level and thoroughly cleared of weeds, all you need to do is sow, water and watch out for pests. Mother Nature will do the rest.
There are also several disadvantages of direct sowing
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Small seeds present challenges - some plants produce extremely small seeds. Sowing these directly can be challenging in many ways, as they’re hard to see and may be carried away by a puff of wind or torrential rain. Such tiny seeds are usually better sown indoors, but if you have ample space and don’t mind taking a risk, you could still try sowing them outside.
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Overcrowding is a risk - leading on from this, it can be tricky to space direct-sown seeds correctly, especially if they’re small and brown. Mixing them with a small amount of light-coloured sand can help. If your seedlings emerge too tightly packed, thin them to the spacing recommended on the seed packet. It may be possible to transplant some of the thinnings so they’re not wasted.
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Young plants are vulnerable - direct-sown seeds are at the mercy of the elements, clumsy feet, and pests ranging from wood pigeons to ants. If you’re concerned about any of these, a temporary covering of fine net or a cloche will help nurse them through the early stages of life. You should expect to lose a higher percentage of seedlings compared to growing indoors, but if you get your timing right, they’ll germinate like cress!
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The growing period is shorter - since the 17th Century, gardeners have been devising cunning ways to extend the flowering and fruiting period of thousands of plants. Sowing under glass is one of them. Direct sowing means waiting until outdoor conditions are perfect for germination, which is typically weeks or months after you could have sown them indoors. For some plants, such as chillies, there simply isn’t enough time for them to grow and bear fruit if direct sown, so the only option is to give them a head start indoors.
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Weeds can creep in unnoticed - unless you are a very experienced gardener, it is hard to tell seedlings apart, creating the risk of weeds being allowed to grow and compete with the plants you want. To avoid confusion, it’s a good idea to direct sow in marked rows, so that it’s obvious which are weeds and which are not. Wildflower seeds are generally broadcast-sown onto the soil surface, so here it’s important to clear the ground of weeds and grasses before you start.
Seeds that grow particularly well if direct sown include courgettes, squashes, French beans, runner beans, peas, carrots, beetroot, rocket, radishes, parsley, sunflowers, nasturtiums, zinnias, cosmos, cornflowers, poppies, calendulas, sweet peas, forget-me-nots, wallflowers, pansies, native wildflowers, trees and shrubs.
Sowing Indoors
Sowing indoors, or ‘under glass’, is most gardeners’ default position. It’s likely to reflect your introduction to gardening at school, with a sunflower in a pot or a bean in a jar on the classroom windowsill. Sowing indoors offers almost total control over the growing medium, temperature, light, and watering, but it creates complete reliance on you. For children, it’s also a fascinating way to observe the early stages of plant growth, which are remarkable by any measure. If you’re hoping to cultivate plants from climates warmer than the UK, indoor sowing may be your only option, and if the seed is scarce or expensive, you shouldn’t take risks with it.
The advantages of sowing indoors
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You have ultimate control - indoor sowing offers the opportunity to create the perfect conditions for seeds to germinate. You can control their exposure to light, water, and heat, and choose different growing media depending on their needs. These will often mimic their natural environment. Serious propagators may invest in growing lights, misting systems and heat mats to help germinate trickier seeds, but most gardeners manage perfectly well with a greenhouse equipped with a heated propagator, or a bright kitchen windowsill.
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It offers maximum flexibility - you can sow seeds indoors for 12 months of the year if you so wish. Many gardeners will start with chillies and tomatoes early in the New Year and continue until December, when it’s time to sow sweet peas. You won’t have to wait for it to stop raining or for the ground to thaw, but most types of seed have an ideal sowing window, which is always indicated on the packet.
There are some disadvantages of sowing indoors
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It's hard work - your plant babies are entirely reliant on you during these early stages, so be prepared to check them once or twice a day and avoid sowing just before you go on holiday.
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Space is at a premium - anyone who has ever owned a greenhouse will tell you that it’s never big enough for the number of seedlings and young plants you want to accommodate in spring. That’s why it’s a good idea to sow those varieties you can outdoors to take the pressure off a little. You’re also going to need a lot of kit - trays, pots and compost - which all have to be stored somewhere.
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There can be bumps in the road - Every time you disturb a seedling by pricking out or potting on, its growth is retarded for a short time while it adjusts. Always handle seedlings gently, by the seed leaves if you can, and avoid breaking or squashing the tender young roots. Sowing seeds direct into wool pots or modules reduces the number of times you need to handle them.
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Light can be lacking - if you’re growing seedlings on a windowsill, they will naturally bend towards the light. You’ll need to turn them daily to keep them straight. Window glass blocks out some light, and if it’s dull outside, you’ll quickly find seedlings become pale, leggy and liable to flop over. This is called etiolation. Before this happens, it’s advisable to get them outside or somewhere brighter but still sheltered, like a porch or conservatory. A little trick to encourage your seedlings to develop sturdier stems is to brush your hand lightly over them a few times a day. This mimics the effect of the wind or passing animals, to which plants respond by beefing themselves up, so as not to get damaged. This phenomenon goes by a tongue-twisting name - thigmomorphogenesis.
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Damping off is always a danger - if your seedlings suddenly collapse, check to see if they’ve gone brown where the stem meets the compost. If they have, it’s a fatal phenomenon that gardeners call 'damping off', caused by fungi in the compost. Although seedlings can also succumb to damping-off outdoors, it affects indoor-sown ones more often. To prevent it, provide good ventilation and avoid overcrowding seedlings. Watering with tap water is also preferable to stored rainwater, which may contain bacteria and fungal spores.