How to Sow Beetroot: Seed Clusters, Depth and Thinning

One seed is really several

What you plant as a beetroot seed is not a seed at all. It is a dried corky fruit holding two to four true seeds, which is why a single sowing point comes up as a tight clump of seedlings rather than one. Nothing has gone wrong. This is normal for beetroot and it is the single fact that decides how you sow and how you thin.

It matters because those seedlings sit within a fraction of an inch of each other and their roots start swelling within weeks. Left as a clump they push each other sideways, stay small, and end up flat and misshapen. A gardener who sows beetroot the way they sow radish, one seed per station and no thinning, gets a bed of leaves and marble sized roots and never works out why.

Some seed is sold as monogerm, meaning it has been bred or milled to a single embryo. Unless the packet says so, assume you are handling clusters and plan on thinning.

Soil temperature and sowing depth

Beetroot germinates over a wide range but is genuinely slow at the cold end. Soil at 50F (10C) can take two and a half weeks; soil at 68F (20C) has seedlings up in a week. Anything above 86F (30C) starts to suppress germination, which is the reason a mid summer sowing often comes up patchy while the same seed sown a month later is even.

Depth is where most sowings are lost. The cluster needs to be covered by about half an inch (1 cm), no more. Bury it at an inch and a half and the seedlings exhaust themselves pushing a corky shell through the soil. Too shallow and the cluster dries out before it can absorb water, and a beetroot cluster needs a lot of water to soften.

Soaking the seed overnight in water before sowing is worth the trouble. The corky fruit contains germination inhibitors that wash out, and pre-soaked seed comes up several days earlier and much more evenly.

Beetroot seedlings will take a light frost once they have true leaves, but a cold snap during the first fortnight after sowing on very young plants can trigger bolting later in the season.

Sowing in a row

Beetroot is direct sown far more often than it is transplanted, because the roots resent disturbance and a checked seedling makes a poor root. Prepare a fine, firm, stone free surface, water the drill before you sow rather than after, and sow into damp soil.

1. Soak the seed overnight Put the seed in a cup of water at room temperature for eight to twelve hours. Drain it and sow the same day. Do not leave it soaking for two days: the clusters begin to ferment and germination drops.
2. Draw a shallow drill and water it Make a drill half an inch (1 cm) deep and run water along it. Sowing into a wetted drill, then covering with dry soil, keeps moisture at seed level without crusting the surface.
3. Space the clusters at two to three inches Set clusters two to three inches (5 to 8 cm) apart along the row, with rows twelve inches (30 cm) apart. This is wider than it looks right, but each cluster is going to become one plant needing four inches of space.
4. Cover and firm gently Draw dry soil over the drill and press it down with the back of a rake. Firm contact matters more than depth. Do not tread it.
5. Keep the surface damp for ten days Water lightly every day or two until the seedlings are through. A crust forming over a germinating cluster is the other common cause of a patchy row.

Thinning to one seedling

Thinning is not optional with beetroot and it is not something to put off. Do it when the seedlings have two true leaves and are around an inch and a half (4 cm) tall, which is usually two to three weeks after emergence. Leave it until they are four inches tall and the roots are already tangled, and pulling one damages the one you keep.

The correct final spacing depends on what size root you want. Four inches (10 cm) between plants gives a tennis ball sized root. Three inches (8 cm) gives smaller, more tender roots and a heavier crop by weight from the same row. Six inches (15 cm) grows the large storage roots, but the flesh gets coarser as they get bigger.

1. Thin in two passes, not one At two true leaves, reduce each cluster to the two strongest. A fortnight later, take out the weaker of those two. Two passes give you insurance against slug losses in between.
2. Cut, do not pull Snip the unwanted seedlings off at soil level with scissors. Pulling lifts the neighboring root with it and any check to a swelling beetroot shows up as a stunted or forked root later.
3. Eat the thinnings Beetroot thinnings are proper salad leaves, not waste. Rinse them and use them the same day. This is the first of several harvests off the bed.
4. Water the row after thinning Thinning loosens the soil around the remaining plants. A watering settles it back around the roots and gets them moving again quickly.

If a whole cluster fails, do not re-sow into the gap once the row is a month old. The late plant will be shaded and will never catch up. Fill gaps within the first two weeks or leave them.

When starting in modules is worth it

The one situation where module sowing beats direct sowing is an early crop, where you want plants ready to go out the moment the soil is workable. Beetroot transplants better than most root crops as long as it goes out young, before the taproot has hit the bottom of the cell.

The trick used by market growers is to deliberately not thin the module. Sow one cluster per cell, let three or four seedlings grow together, and plant the whole clump out at eight inches (20 cm) spacing. The roots push each other apart as they swell and you get a cluster of medium sized beets from one planting hole.

What to write down

Beetroot is a crop where one season of notes removes most of the guesswork from the next. Record the sowing date, whether you soaked the seed, the date the first seedlings broke through, and the date you finished thinning. The gap between sowing and emergence tells you whether the soil was warm enough, and it is the number you will want when you decide how early to risk sowing next year.

Also note the final spacing you used and the size of root it produced. Most gardeners find they have been sowing too close for years, and the only way to see it is to have last season's spacing and last season's harvest weight written next to each other.