Fill your sill: a guide to windowsill growing

Windowsill growing is a great way to inject a little green into your interiors

Windowsill growing is a great way to inject a little green into your interiors - Credit: Getty Images/moodboard RF

Urban gardens needn’t be small and shabby. In celebration of National Gardening Week, we demonstrate the art of windowsill growing.

Watercress growing in eggs shells on window sill

Watercress growing in eggs shells on window sill - Credit: PA Photo/thinkstockphotos

You don’t need a vegetable patch to start growing - just a sunny windowsill.

So says Guy Barter, RHS Chief Horticultural Adviser, who is joining his colleagues in trying to encourage newcomers to grow plants during National Gardening Week.

During the week, the RHS gardens are hosting activities to showcase the benefits of gardening and inspire new gardeners to engage with nature at all levels.

Meanwhile, Guy and his RHS pals have been growing all sorts of things on their own windowsills, to prove that it’s possible to create an edible indoor veg patch.

So, what have they been growing? Guy gives us the low-down.


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The modern equivalent of mustard and cress, now a wider range of seedlings are grown, including basil, beetroot, carrot, celery, dill, kohlrabi, leek, perilla (from the mint family) and Swiss chard. Ideally use seed sold for microgreens as this will germinate well and evenly, and will be free of any unwanted materials. If in doubt, rinse seed well in several changes of fresh water before sowing.

Sprinkle seeds on to trays containing 25mm (1in) peat-free potting media or on to damp kitchen towel, in a seed tray or plastic box. Smaller containers are more manageable - half seed trays (23cm x 17.5cm x 5cm) are ideal. Use containers with drainage. After light watering, place the seeds on a warm, sunny windowsill and allow to germinate. Plenty of warmth is needed for germination and a heated propagator is helpful where the central heating is not turned high. Too much heat on the average windowsill will result in ‘leggy’ seedlings - if this happens, move the trays to a windowsill in a cooler room.

Water seedlings as required as they won’t put up with drying out or being drowned. Once they reach 5cm high, they can be cut with scissors and used as soon as possible. They will keep in the fridge in an airtight box for a day or two. Expect crops to take two to three weeks to complete their life cycle at room temperature (18-22C).


Tops and bottoms discarded when preparing supermarket vegetables can be planted in pots of peat-free potting compost, suspended in water or placed on damp kitchen towel in a seed tray or plastic box, and kept in a light place at room temperature (18-22C). They will often grow and send out new leaves, which can be gathered as they become big enough, and used in salads and garnishes. Best results come from leaving 25mm (1in) of vegetable below the top. The ‘tops’ may well root and grow for some time, but eventually they will weaken and be consigned to the compost bin. Tops: carrots, swedes, turnips. Bottoms: cos lettuce, leeks, onions, salad onions.


Pumpkin seed sprouts are among the quickest ‘crop’ you can grow. Ideally use hull-less or naked pumpkin seed such as Baby Bear. Most pumpkin seeds have a hard seed coat, requiring you to ‘shell’ the seed. Soak them in water for up to four hours at 16-18C and consume the softened seeds. Alternatively let nature take its course and place your seeds in a sprouter (container with a sieve-like lid) and rinse and drain the seeds every 8-12 hours until they send out a rootlet, when they can be eaten. Don’t fill the sprouter by more than half.


Potted herbs from the supermarket have had a pampered life in perfect greenhouse conditions and are meant to be taken home, the leaves eaten and then discarded. But if you lightly trim them for immediate use and place them on a sunny windowsill in an unheated room, they may regrow. Best results come from leaving 50cm (2in) of stem rather than shaving the plants. Divide them into four and re-pot in a peat-free potting compost. Water with dilute fertiliser such as seaweed fertiliser.


The same scrupulous cleanliness is advisable when growing microgreens and sprouting seeds as when preparing food in the kitchen. All equipment should be washed in hot water and detergent, and seeds sold specifically for sprouting and microgreen production are preferable, as these will germinate evenly and be free of harmful organisms.

:: National Gardening Week runs from April 10-16. For more information visit