Carrots do not need much warmth to start germinating and begin to grow, but it is still too early to sow into the vegetable beds. Even though they have been covered with black weed fabric, which will help the soil to warm more quickly, it will be a while yet before the soil is suitable for direct sowing. Seed sown too early into cold wet soil is likely to rot before it can germinate and grow away, and even where they do germinate, later sowings made when conditions are improved will typically perform better. Neither can carrots be started sensibly in, say, seed trays or modules, as they form their all important tap root soon after germination. Carrots are not, therefore, a crop to be transplanted.
If a little extra warmth can be offered, from a greenhouse, polytunnel, cold frame, or perhaps even a cloche, then an early sowing may be attempted and mid February is perhaps a good time to consider it. Our greenhouse has soil beds but they are much too rich for carrots due to the abundance of horse compost that we add each year. Carrots need a light textured soil that is lower in nutrients and particularly low in nitrogen. For this reason, we started these seeds in pots.
We are using the same 15 litre pots in which we start our earliest planting of first early potatoes. This is about the same size as a builder’s bucket, perhaps a little larger, and is, I think, a reasonable size for carrots. The potting mix for carrots is ideally light in texture and free draining. A mixture of equal parts sand and organic compost is likely to be well suited. In our case we had available a locally produced organic multipurpose compost that was a blend of around 30% top soil and 70% composted green waste. The mixture is reasonably fine, though with the usual twiggy bits one might expect to find. We sieved it before use to remove the larger pieces but otherwise it has a pleasant texture. As it has some top soil in the blend we used two parts of this compost to one of sand.
After some consideration I decided not to add further feed. I could have added a little fish, blood, and bone and perhaps a little extra bone meal, but it is important not to provide an overly rich environment for carrots and, in particular, not too much nitrogen which would result in poor quality roots. So, a little balanced feed or one low in nitrogen could be used if needed but may not be necessary depending on the compost blend being used.
For an early sowing in pots we wanted varieties that would be fairly quick to mature and give nice young roots. We chose Chantenay (from Seeds of Italy) and Amsterdam Forcing (from Premier Seeds Direct) and sowed two pots of each.
Germination of carrot seed can be a little patchy and fresh seed is ideal. They can either be station sown with two or three seeds per station, spaced an inch or two apart, or then seed can be simply broadcast across the surface of the compost. We elected to do the latter and will probably have to thin a little to leave an inch or so between seedlings. We covered the seeds with vermiculite, which should help keep them suitably moist, though a fine sprinkling of compost would also serve.
The pots have been placed in our greenhouse, near to the south facing wall where they will have most protection. It is an unheated space, but conditions should be suitable for much of the time, and if another harsh cold period is expected a little extra protection may be offered with some fleece. Germination may take a week or two, then we can thin the seedlings a week or two after that when they are large enough to handle. For now, it is just a case of keeping the compost moist and being patient.
Our later sowings will be in the vegetable beds, but if suitable soil cannot be provided for carrots then a succession of pots could be sown – say, one or two every two or three weeks – from around mid February though to the middle of summer to provide a succession of harvests.