Sow carrots in August: your second chance for an autumn harvest

Frau Schneider asked this week whether it was too late for carrots.

She sowed in May, but the top layer of soil dried out during a heatwave before the seeds could germinate. The rows stayed empty, and now, at the start of August, she is looking at a half-empty raised bed.

"Stachi, is there any point? Have I missed my chance?"

You haven't missed anything. August is the second window — and for an autumn harvest, it might even be the better one.

Why autumn carrots taste sweeter

This sounds like marketing, but it's biology.

When temperatures drop in September and October, carrots convert some of their stored starch into sugar. It's a survival mechanism: a higher sugar concentration in the cell sap lowers the freezing point, so the roots are protected from frost damage. The plant is protecting itself.

A carrot pulled from the ground in late October tastes noticeably different from a summer one — distinctly sweeter, less earthy. That's not imagination. That's chemistry.

Frau Schneider will notice on the first bite.

The sowing window

In the Swiss Midlands — Zürich, Berne, Lucerne, the Berikon area — sow by 10th to 15th August at the latest. Earlier is better.

Carrots need 70 to 90 days to mature depending on the variety. Sow in early August and you'll be harvesting from early to mid-October. Sow by the 15th and you'll be harvesting in late October — when the first night frosts arrive. A simple fleece cover handles that without any trouble.

In warmer areas like the Rhine Valley or southern Switzerland: you have another two to three weeks. Early September is still possible there.

Why raised beds suit carrots so well

Carrots don't like obstacles. When the soil is too compacted, too stony, or too shallow, they grow around the problem. The result is forked, branching roots — amusing to look at, but annoying in the kitchen.

In a raised bed this rarely happens. The soil is deep, loose, and well-aerated. Carrots can grow straight and long with nothing in their way.

Depth matters: at least 25 to 30 cm of loose soil. If the bed is relatively new and the fill is still loose, you're in good shape. If the soil has settled over the years, it's worth loosening it with a fork first and working in some fresh growing medium.

Don't put fresh compost directly under the seeds. Too many nutrients right below the seed makes carrots fork — the roots grow outward chasing the nutrient gradient. Well-rotted older soil without extra fertiliser is better.

How to sow

Carrots are sown in shallow rows, not in individual holes.

Draw a groove about one centimetre deep with your finger or a stick. Drop seeds in every one to two centimetres. Press the soil down lightly, then water well.

Row spacing: at least twenty centimetres.

Now the critical part — the one that goes wrong most often in summer: the germination phase. Carrots germinate slowly, seven to twelve days. During this time, the top layer of soil must never fully dry out. In August that means: water in the morning, check at noon, water again in the evening if needed.

A light-coloured garden fleece laid loosely over the surface holds moisture and shades off some heat. Not a black fleece — that heats the soil, which carrots really don't like.

This is what went wrong for Frau Schneider in May: not enough water in the first ten days. This time she knows what to focus on.

Thinning — even when it feels wrong

When seedlings are about five centimetres tall, thin them to five to six centimetres apart.

I know it feels strange. You've waited ten days for these seedlings and now you're pulling most of them out. But closer spacing means the carrots crowd each other, stay thin and small, and none of them develop properly.

The thinned seedlings are edible. They taste of delicate carrot with a slight bitterness — good in salad.

Watering until it turns cold

Once the plants are well established, carrots don't need daily watering, but they do need it to go deep. Watering thoroughly once or twice a week is better than a little every day at the surface. Deep watering encourages deep root growth.

As October arrives: a fleece cover protects the foliage down to around minus four or five degrees Celsius. The carrots in the soil can take even more — earth is a good insulator. Leaving them in the ground and harvesting after the first frost gives the sweetest result.

What Frau Schneider is doing now

I told her: one row, maybe two, wherever there's space. Loosen the soil. Draw a shallow groove. Drop in the seeds. Water well. Keep it moist for ten days.

"And what if nothing comes up again?" she asked.

I explained: this time it's all about water. Carrots in summer heat only germinate if the top layer never properly dries out. That's the one trick.

She'll write to me at the end of October.

🦔 Stachi