Window Box Veggie Gardening

The idea of window box farming sounds delightfully quixotic and impractical. Actually, it’s an invitation to those who look longingly at other people’s veggie patch and think, ‘I wish I had the space.’

You could hardly get smaller than a window box but the possibilities are almost endless for growing your own fresh green stuff and even hot stuff like chillies or juicy tomatoes.

First things first!

You need to find the right window, balcony, deck or patio for your window boxes. Most edible plants need plenty of sun, but shelter from blazing heat, wind and winter cold. The best position would be north or east facing.

Safety foremost

A window box gets heavy when filled with soil and vegetables, even lightweight plastic containers. If not securely fixed in place they can be deadly objects, literally. Experienced window box farmers suggest using brackets to secure the window boxes which should sit a few centimetres below the windowsill so that upright growing plants have more room to spread and won’t block the window.

When using window boxes on a balcony or deck, the safest option is to attach the window boxes so that they are on the inside of the balcony or deck. Even better, make or find stands on which to put the window boxes so that the tops are just level with the edge of the balcony. However, if space is an issue, and the window boxes are on the outer side, there must be absolutely no danger of the window box dislodging.

Types of containers

Opt for the lightest ones you can find, unless there is a secure base which makes it possible to consider heavier types like terracotta, cement or steel. Plastic window boxes retain moisture better and they’re lighter.

To grow vegetables successfully, your window box should be 20 to 30cm deep and at least 15cm wide. It should be the same length as the window. There must be adequate drainage holes and it’s a good idea to have trays/saucers underneath to catch the water so that it doesn’t run down the walls or into the balcony below.

READ MORE: Growing veggies in buckets

Soil mix

Use the best quality potting soil, not ordinary garden soil. However, commercial potting soil does not contain enough nutrients for vegetables. Two options:

Use a commercial mix and add earthworm castings, an organic, slow release 2:3:2 fertiliser, vermiculite for good water retention and agricultural lime (also called dolomitic lime) which contains calcium and magnesium, as most edible plants like a higher level than is present in commercial potting mixes. Line the bottom of the container with hessian cloth or weed control fabric to ensure good drainage before filling it.

Make your own mix, using equal quantities of compost, vermiculite or perlite and palm peat, that comes in a compacted brick form and needs to be soaked in water. To ensure the correct carbon content consider adding EcoBuz HumiGro in granular form or as a drench. Add in slow release 2:3:2 fertiliser and 2 tablespoons lime.

Best veggies for window boxes

Obviously the most suitable vegetables, herbs and edible flowers for window box farming are those with compact, low growth and roots that don’t require deep soil.

Herbs: thyme varieties, oregano, marjoram, sage, parsley, mint (in a pot on its own), chives, coriander, chervil, rocket. Basil and rosemary grow into large plants but you can start them in window boxes and harvest or prune regularly to keep them a manageable size.

Leafy greens: loose leaf lettuce, ‘Simply Salad’ green mixes, Swiss chard, baby spinach, Asian greens (for winter and spring), kale.

Root veggies: baby carrots or ‘Carrots Parisienne’ (round root), beetroot, radishes, turnips (winter), spring onions.

Legumes: bush garden beans are a very easy and productive veggie, especially for beginners.

Fruiting edibles: compact tomatoes like ‘Window Box Red’ to sow from seed and compact patio varieties like cherry tomatoes ‘Tumbler’ and ‘Orange Zinger’ or Roma tomato ‘Little Napoli’, dwarf capsicum jalapeno (‘La Bomba’), mini-sweet peppers (‘Cute Stuff’ and ‘Pot Peppers’) as well as patio strawberries like ‘Delizz’, ‘Toscana’ and ‘Summer Breeze’.

Flowers: edible flowers like nasturtiums, pansies, and violas as well as alyssum, lobelia, marigolds and calibrachoa to attract bees.

Getting started

Fill the window box about two thirds of the way with soil, then place in the plants and fill with soil, leaving about 3cm of space from the top of the window box so that the water does not spill over when watering.

Plants in window boxes can generally be planted close together but be aware of the space each plant needs for leafy growth and root development. Don’t be tempted to over plant, as crowded plants become susceptible to pests and diseases.

Mix it up

Consider growing aromatic herbs with the veggies to deter pests and some flowers to attract bees for pollination. Sow from seed or plant seedings, either will work. Some veggies like garden beans, baby carrots, beetroot, radish, turnips, baby leaf spinach, and spring onions, are best sown directly into the soil. When planting seedlings, make sure the root ball is wet before planting into the damp potting mix.

Caring for you window box plants

Watering: this is the most important aspect of care. Vegetables need consistently moist soil, and they suffer if the soil dries out. That’s the one drawback of window box gardening. Because the containers don’t hold much soil, they dry out quickly. In midsummer they may need to be watered twice a day.

Water during the day, or early morning, rather than at night as this could make them susceptible to fungal diseases.

Consider installing an automatic drip irrigation system like the do-it-yourself Gardena Micro-Drip-System for balconies and patio pots. www.gardena.com

Feeding: Most vegetables are heavy feeders and need supplementary feeding with a liquid fertiliser at least once a month, ideally twice a month. Top up the growing mix with compost during the growing season.

Pests and diseases: Use organic or biological pesticides and fungicides to control pests and diseases. The best way to prevent infestations is to ensure that there is good air circulation, that the leaves do not stay wet at night and that plants are not drought-stressed or nutrient-deficient.