How much sun does a vegetable garden actually need?

December 24, 2024

Six to eight hours of direct sun is the number everybody quotes for a vegetable patch, and it is a reasonable starting point. It is also only half the answer, because around here the thing that ruins a bed in January is not a shortage of light, it is the afternoon heat that comes with it.

The simple rule, which covers most of it

If you eat the fruit, it needs the most sun. Tomatoes, capsicums, chillies, zucchini, cucumbers, pumpkins and beans all want the sunniest spot you have, because they have to make a fruit and that takes energy.

If you eat the leaf, it needs the least. Lettuce, silverbeet, rocket, spinach and most of the herbs will do perfectly well on four or five hours, and in a South Australian summer they will do better with some afternoon shade than without it, because heat is what sends them straight to seed.

Root crops sit in between. Carrots, beetroot and onions want a good half day.

Morning sun and afternoon sun are not the same sun

This is the part that gets left out of the standard advice, and it matters a lot more here than it does in a cooler climate. Six hours of morning sun is gentle and useful. Six hours of afternoon sun in February is punishing, and it will scorch leaves and cook the soil while the plant is trying to hold water.

So when you are picking a spot, a bed that gets sun until about two and then falls into the shade of the house is often better than one that bakes from midday until dark. Especially for anything leafy.

Check the spot in winter, not just now

The sun sits much lower in the sky in June than in December, so shadows are far longer. A fence, a shed or a neighbour's tree that casts nothing across the bed in summer can put it in shade for most of a winter day, and people plant a bed in spring and then wonder why nothing moves in the cold months.

Spend a bit of time watching where the shadows actually fall before you build anything. A few notes on your phone over a week is enough, and it is the cheapest thing you will ever do for that garden.

What to do about too much sun

Mulch. The single most useful thing. A good layer keeps the root zone noticeably cooler, slows evaporation and stops the surface crusting over. Keep it back off the stems.
Shade cloth over the worst of it. For vegetables a 50 per cent cloth is the one you want. The heavier 70 and 90 per cent cloths are made for other jobs and will cost you the crop if you throw them over a veggie bed.
Water deeply and less often rather than a light sprinkle every day, so the roots go down after it instead of sitting at the surface where it is hottest.
Use taller crops as shade. Corn, climbing beans on a frame or a row of sunflowers on the western side will take the sting out of the afternoon for whatever is behind them.

What to do about too little

Grow the leaf crops there and put the tomatoes somewhere else. That is genuinely most of it. A shaded bed is not a failed bed, it is a salad bed.

Pots are the other answer, because you can move them and chase the light through the year. It is more watering, so it is a trade rather than a free win, but for a courtyard or a rental it is often the only sensible option.

One thing worth saying, since it comes up: don't use mirrors to bounce light into a shady corner. It concentrates heat onto whatever is in front of it, and on a hot day that is a scorch risk at best.

Shop related products

Martins Organic Sugar Cane Bale 11kg. Breaks down into the soil as it goes, so it feeds while it mulches.
Easy Wetta Garden Mulch 50L. Handy bag size for a bed or two, and it lets water through rather than shedding it.
Neutrog Whoflungdung Mulch 20kg. Composted, so it does more for the soil than a straight bark would.
Brunnings Garden Compost with Seaweed 25L. For working through the bed before you mulch over the top.

Seeds are in the DT Brown range and everything else is in the garden centre. Bales and bags are awkward in a car boot, so local delivery is $5 in Strathalbyn and $10 on the regional run.

Did you know we also cut shade cloth off the roll in the shop, by the metre, in 1.8 and 3.6 metre widths and in 50, 70 and 90 per cent. We have garden stakes in 900mm, 1.2, 1.5 and 1.8 metre lengths and seed raising mixes as well. None of that is on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.