What supplements, organic fertilizers, or gardening practices can help my root vegetables grow better?


I have very satisfactory success growing all the vegetables I want to grow except beets, carrots, and parsnips. These vegetables take far longer to develop a swollen root than they should, and never get to a good size. I am an organic gardener, and my soil tests are good in all areas except iron, which is quite low. The UMaine lab suggested not adding iron. I have good quality loam with compost added yearly in raised beds. The crops get plenty of water when needed. Please help me with any suggestions for supplements, organic fertilizers, or gardening practices that might help me make my root crops grow more successfully.


Liz Stanley, Horticulture Community Education Assistant, Knox-Lincoln Counties

If you’re having problems, soil testing is a good place to start. One thing that a soil test can’t do is determine your soil’s texture. For instance, carrots require “deep, loose, and fertile sandy loams and peat soils with good moisture-holding capacity” for the straightest and smoothest roots. Clay soils are not ideal because of compaction. Soils that are very high in organic matter (common in raised beds) grow great squash and pumpkins, but root vegetables prefer a more mineral-based soil.

Other factors may be:

  • Heat. Most root vegetables prefer cool soils. Raised beds tend to be warmer, and last year was a very hot growing season.
  • Moisture. Root vegetables need well-drained soil but consistent moisture, especially during germination. As the plants mature, too little and they’re stunted. Too much and they split.
  • Full sun is important for top and root development.
  • pH preferences for different crops can vary but root crops generally like a range between 6.0 – 6.5.
  • Adequate spacing makes larger roots and is usually managed by thinning the seedlings early.
  • Fertility is best done by side dressing gently after the plants have started to grow. Fertilizers are salts, so doing it too early can “burn” the roots. Later on it can cause sudden growth that makes them split.
  • High levels of nitrogen (from manure, compost or fertilizer) in relation to phosphorus and potassium will result in heavy leaf production with poor root development.

A great resource for Maine gardeners is the Johnny’s Selected Seeds catalog. They have very specific cultural information for each crop and how long plants take to mature. Here’s cultural information about beets under the pull down menu in “growing information”.

Another excellent resource is the New England Vegetable Management Guide.

Root crops in general are the first ones to plant and the last to harvest, so they’re in the garden for a long time. For that reason, they’re not always the most productive crop for home gardeners.

I hope this is helpful and feel free to watch our video series – Victory Gardens for Maine.