Carrots are not particularly demanding of soil fertility, but they can be difficult to grow.  Although soil fertility need not be high, carrots don’t like acid soils, use lime to bring the pH to near 7. Another requirement is that the soil be deep and free from rocks or other large objects, which will cause the roots to fork. A high content of organic matter is helpful, but it is essential that the organics be well-rotted, so that the chunkiness of the organic material doesn’t split roots. Carrots love potassium, so amending soil with wood ash, a source of readily available potassium, is helpful.  High nitrogen fertilizers should be avoided, as nitrogen promotes the formation of hairy roots.

Typical fertilizer recommendations for western Pacific Northwest soils are:

  • Nitrogen: 50-100 (N) lb/acre
    Phosphate: 100-160 (P205) lb/acre
    Potash: 80-150 (K20) lb/acre
    Sulfur: 30-50 (S) lb/acre

Getting good, even germination of carrots can be a frustrating experience, for a number of reasons –

  • Carrot seeds are tiny, so extreme care is required to achieve good seed spacing.  If plants are allowed to mature with a spacing of less than 1-2″, the carrots will form small, distorted and intertwined roots.  If seeds are sown too thickly, you will spend an eternity thinning the plants to the required spacing.
  • On the other hand, carrot germination rates are extremely sensitive to a variety of conditions, so if you carefully sow seeds with 1″ spacing, you may end up with a lousy yield of widely spaced roots.  Carrots germinate extremely slowly, especially if the soil is too cool (below 50 F) or too warm (above 75 F), and the soil must remain evenly moist during the entire germination period.  Even brief drying out of soils with high clay content may produce a surface crust that the wimpy carrot seedlings cannot penetrate.  For these reasons, in many soils it may be necessary to cover seeds with potting soil or finely sifted compost, rather than garden soil.  Aim to sow about 1/4″ deep.
  • Virtually every weed seed known to man will germinate faster than the carrot seeds, and the weeds will likely grow high enough to obscure the carrot plants entirely before the carrot plants are robust enough to survive howing.  Thus, it is essential that carrots be sowed in the parts of your garden where you were particularly vigorous about suppressing weed growth the previous year.
  • Carrots respond well to the use of floating row covers. Covers should be can be applied immediately after seeding and should be removed at about the 7th true leaf stage.

Since my cool coaster climate requires me to grow heat loving plants like tomatoes, peppers, and eggplants using black polyethylene sheeting, and such plastic covers are really effective in suppressing weed growth, I have good success planting carrots in beds that held tomatoes/peppers/eggplants the prior year.  Raised beds are especially helpful for carrots, because these provide for the deep uncompacted soil that carrots require.