A seedbed is a protected environment for germinating and nurturing seedlings that will eventually be transferred to the vegetable patch and flower beds. Instead of sowing seeds, if you use a seedbed to produce seedlings for transplanting, you can sow them early, select the strongest plants, transfer them at the right time and into the right space in your vegetable patch, and stagger the harvests. Then, after transplanting, you have less work to get rid of weeds.
In your seedbed you can sow most vegetables. The few exceptions include root vegetables (e.g. carrots). Here we offer you our tips for creating a DIY seedbed where you can grow seedlings for your vegetable patch in the open ground or, in the colder months, under a cold frame.
How to build a DIY seedbed
In practice, a seedbed is a greenhouse where you can develop seedlings to be planted in the vegetable patch at the appropriate time of year, which varies depending on the vegetable. We call it a "protected environment" because it offers seeds an ideal temperature in which to sprout and start growing, but also the right humidity and controlled conditions (free from weeds, disease and parasites).
Seedbed come in all shapes and sizes, the important thing is that it is exposed to heat and sunlight. It basically consists of a structure, or at the very least a simple container, with a plastic, plexiglass or glass transparent covering. You can buy one ready for use or make your own, either buying what you need or using what you already have at home. It is better to use materials that are moisture resistant, waterproof and insulating; if they are repurposed materials, make sure they are clean, so that they don’t create a breeding ground for pests and disease. To clean more robust containers you can use a high-pressure washer.
You can build a DIY seed greenhouse with:
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A wooden frame with transparent cover installed somewhere in your vegetable patch (therefore possibly leaving you with less space to grow vegetables in).
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A wooden or metal structure with transparent walls and roof in which to store sowing containers. The dimensions should fit your available space and needs: it can be anything from a shelf to a stand-up space furnished with tables and racks.
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A box made of plastic (lined with non-woven fabric) or polystyrene and filled with soil, closed at the top with a transparent lid.
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Lots of small soil-filled pots placed in a tray. In this case you can buy dedicated seed pots, which should preferably buried at the time of transplantation (if made from biodegradable paper, for example). Alternatively, to set up your DIY seedbed you can reuse old plastic or polystyrene seedling trays, disposable plastic cups, the bottom of plastic bottles, yogurt pots, plastic and cardboard egg trays, as well as ice cream cups, cardboard toilet roll tubes and egg shells.
To build a DIY seedbed made of wood, you can buy the material and assemble it, or cut wooden planks from a log. In any case, it is essential to be equipped with a chainsaw and chain-resistant clothing.
How to prepare your homemade seedbed
Place the DIY seedbed in a place that is exposed to the sun, but sheltered from wind and rain (i.e. on the south or southwest side of the garden). If you have a small mobile seedbed, keep it indoors next to a sunny window. Even if the seedbed is not in the house, but well positioned, it will receive sufficient heat from the sun; if, on the other hand, you need extra warmth, you can use heat mats and warming cables, which go under the seed pots or trays. An alternative is to buy small heated propagators.
Heating mats and warming cables simulate what happens naturally in a hotbed. A hotbed is a bottomless wooden box with a transparent lid—the seedbed—placed above a hole in the ground filled with fresh manure, which keeps the seedbed warm through fermentation.
To prepare the bed of your homemade seedbed, buy some seeding topsoil, which is very fine and sterilised to ensure it is free of parasites and weed seed. It is used alone or added to screened soil and compost. You can make it yourself by sieving and mixing earth, sand and peat. Apart from the composition, make sure that the substrate for the seedbed is well-draining and soft, so that water does not stagnate and the roots of the seedlings can develop.
You can also make your own compost, which is excellent way to replenish the garden soil that will accommodate your plants with organic matter: here is our guide to DIY compost.
How to sow and care for seedlings in your seedbed
To guarantee good results from your seedbed, use quality seeds, not old or poorly preserved ones. Follow the planting instructions indicated on the sachet, which are specific for the type of vegetable: period, terrain, depth, minimum germination temperature, humidity etc.
The seedbed can be a common surface (if sowing in an unsegmented tray, for example), suitable for broadcast or row sowing small-seed vegetables (like peppers). Or it can be segmented into individual cells, where you can insert a single seed: this system works for large-seeded vegetables (like courgettes). If the seedlings in your seed tray are too closely spaced, thin them out by selecting the best ones. If you want a tidy seedbed, we recommend that you use one tray per species and label it.
Seeds and seedlings should be gently sprinkled with water—a small watering can with a sprinkler attachment is perfect—or by spraying water through a mistblower. In the case of finer seeds, it may be more practical to soak the pots or trays in a container. Either way, DIY seedbed containers need to have good drainage, so in order to avoid water accumulation, pierce the bottom of repurposed plastic containers. Rainwater or groundwater (at room temperature) is preferable to tap water, especially if the latter is chlorinated. Even water drawn from a ditch using a water pump will do, as long as it’s not polluted.
Remember to scarify your DIY seedbed during the hottest days and hours in order to eliminate humidity and avoid condensation, which promotes the development of fungal diseases. Also keep an eye out for snails.
How to plant seedlings in your DIY seedbed
Transplanting is a critical moment that causes stress to the seedlings in your homemade seedbed. When you extract them from the seeding container, if the root ball is held firmly together by the roots, it means they are ready to transplant: the time elapsed since seeding depends on the type of vegetable and the temperature. Before planting them, it is best to let them acclimate a while outside the seedbed and inside their containers, then:
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Dig a hole as deep as the root ball or slightly deeper.
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Wet the root ball and insert the seedling into the hole.
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Fill in the hole and press around the base of the seedling to eliminate air pockets and make the soil adhere to the roots.
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Water carefully, and abundantly if the weather is hot.
Ensure adequate inter-row and intra-row spacing of the vegetables, otherwise they may suffer stunted growth or even die. When arranging the plants inside the vegetable patch, take into account crop rotation and companion planting: we talk about this in our article on getting the most out of your vegetable patch.
Before transplanting till the soil using a rotary tiller (here you can read our vegetable patch preparation guide). Good soil quality is actually essential for a successful harvest, so help to ensure it by taking all the necessary precautions for improving soil fertility.
Lastly, here are our seasonal tips on how to keep the vegetable patch healthy in winter—the ideal time for growing plants in a DIY greenhouse—and how to protect the vegetable patch from the heat.
