Skip to main content

2021 Considerations: Raising Root Vegetables Right

Authors: Natalie Hoidal and Marissa Schuh, Extension Educators, University of Minnesota Extension

Our biweekly crop by crop growing season prep series continues.  This week we dig deeper into root vegetables.  Get your stew mix ready, let’s talk carrots, beets, radishes, and turnips.

Image: Howard F. Schwartz,

The Perfect Seedbed: Is it really neccessary?

Conventional wisdom regarding seedbeds for small-seeded crops like carrots and beets is that a perfectly smooth seedbed is necessary for good germination. Clods on the surface can smother small seedlings, and an uneven soil surface can result in variable seeding depths and access to moisture. However, in recent years, growers using no-till and reduced till methods have challenged me on this idea with two main strategies to avoid perfect seedbeds: 

  • Using row cover right around the time that you expect your seeds to germinate and leaving it on for a week or two helps to hold moisture near the soil. While this doesn’t solve the issue of clods, it does significantly help maintain moisture in the top couple inches of soil, and growers seem to have good success germinating carrots this way in reduced tillage systems. 

  • More and more growers are using PaperPot transplanters for small seeded crops like beets. 

Regardless of the smoothness of the seedbed, carrots and beets are finicky and require constant moisture. Invest in irrigation for the first couple of weeks. This is especially important in soils that are prone to crusting; keeping the soil moist helps to prevent crusting on the surface.

If your soils are prone to compaction, consider growing on raised beds. In some recent trials in Waseca (soon to be published), one of our colleagues found that he got higher marketable yields from raised beds compared to flat ground. The raised beds were less compact, and produced nicer, longer, less stubby carrots. 

The value and risk of frost

Carrots, parsnips, rutabagas, and beets all tend to become sweeter after a light frost or two, and so the standard practice for fall root vegetables has been to wait until after the first frost to harvest.  However, in recent years we’ve seen incredibly wet fall weather, to the point that farmers have struggled to get into the fields after the first frost. 

One approach to minimize risk is to utilize succession planting. By harvesting some carrots and other root vegetables earlier, you will lose the flavor benefits of a frost, but you also reduce the risk of losing vegetables due to muddy fields. Carrots are fairly forgiving, in that they can be left in the ground for a couple of weeks once mature. Keep an eye on the weather forecast, and consider harvesting early if there is quite a bit of rain forecasted around the time you plan to harvest.

If you’re experiencing any disease pressure or Aster Yellows, root vegetables should be pulled quickly to prevent problems from spreading. If left in the ground too long, they can become woody and bitter. 

Weeds, weeds, and more weeds

Weed control tends to be more of a challenge for most growers than insects or diseases. This is true for a couple of reasons: it doesn’t make much sense to grow carrots with any type of mulch due to the planting density, so it’s harder to exclude weeds that way. Carrots can also be slow to get started and have a less dense canopy than some other vegetables, so they aren’t as good at out-competing weeds. 

2-3 weeks of stale seed bedding before planting can dramatically improve weed management. The idea of a stale seedbed is: prepare your bed as if you were going to plant, and then wait a week or two until your first flush of weeds emerges. Get rid of those weeds with mechanical cultivation, flaming, or herbicides, and then plant your main crop. You can usually squeeze in a cultivation pass or flame weeding right after planting as well if you have a sense of when your crop will germinate. 

As a trick in carrots, you can plant a few radishes at the end of your rows since they'll germinate about 2 days earlier. As soon as they germinate, you can do your final flame weeder or shallow cultivation pass. After that you're limited to between row weed control and hand weeding.

Getting to the Root of Insect Issues

Wireworms are elongated, smooth, and yellow-brown. Their feeding is detrimental in root crops as they feed on the marketable part of the crop. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo,

On farms where new ground is entering vegetable production, wireworms can be a problem.  Wireworms are typically .5-1.5 inches in size, brown-orange in color, and somewhat armored (as opposed to soft-bodied insects like cabbage maggot).  Wireworms like to feed on the roots of grasses, so we most often see them in places where the field was previously fallow, in CRP, pasture, or even in grass cover crops.  Wireworms burrow into the roots of crops, be it the root of a transplant or the thing we actually harvest in the case of root crops.

The easiest way to manage this pest is to avoid them entirely. When new areas are brought into production, wait a few years before planting root vegetables there.  While any wireworms present will feed on whatever there, the damage to non-root crops is rarely economically damaging.  Wireworms are long-lived in the soil (some species are wireworms for 5 years before becoming harmless beetles), so keeping root crops out for a few years is a good idea.

Treating wireworms involves multiple steps and the products are not easy to use.  For more information, see VegEdge and the Midwest Vegetable Production Guide.

A regularly appearing pest in some Minnesota farms is cabbage maggot.  See the Brassica Bonanza article for the rundown of this pest’s biology.  For root crops, row covers provide very effective control as well as they are placed at the right time and brassicas are being rotated.  Timing can be difficult to nail down, as cabbage maggot adults look similar to houseflies, allowing them to emerge and start egg-laying unnoticed.  University of Minnesota uses weather data to estimate cabbage maggot adult emergence.  These are presented in maps that can be used to figure out when cabbage maggot adults are flying in your area, letting you know when to put out row covers.  These will serve a dual purpose, excluding insects, but also potentially boosting the size of the root crops underneath.

Spots, Specks, and Stunting: Common Disease Issues

Root crop disease prevalence and damage is crop and disease dependent. The most common ones primarily attack foliage, so their management can be important for yield, as well as for growers whose harvest methods rely on pulling the tops of plants.  

For disease issues in the roots before and during harvest, it is a good idea to get a formal diagnosis from the plant disease clinic, especially if the root vegetable is an important crop on your farm.  Soil-borne diseases are often long-lived and can involve a lot of cultural management to keep them from moving around.  Because of this, it is good to know exactly what you are dealing with.

For carrots, foliar disease to keep an eye out for are Alternaria and Cercospora.  Carrot cercospora is not particularly common in Minnesota, and Alternaria is kept at bay on man farms by using resistant varieties. If pulling tops for harvest, it is worth keeping an eye out for them.  

Another carrot disease that is occasional a problem is aster yellows, a disease spread by Aster leafhopper.  This disease is managed through watching out for leafhoppers (whose feeding itself doesn’t do economic damage) and sorting out carrots with aster yellows. Leafhoppers tend to arrive a bit later in the summer, but this is dependant on weather patterns.  Leafhopper populations are higher in hot dry years. In general, planting earlier can help you to avoid them.  Generally, management of the leafhoppers are not necessary.  If you are having consistent aster yellows issues, visit the Midwest Vegetable Production Guide for management information.

Plants infected with aster yellows will have distorted and shrunken tops.  These plants should be pulled, as the carrots will be bitter.  They also serve as a source of inoculum. 

This carrot has been fed upon by a leafhopper carrying aster yellows, causing growth post-infection to be distorted. Photo: Whitney Cranshaw, Colorado State University,

Carrots expressing a range of aster yellows symptoms, from bumpiness to hairiness to stunting. Photo:Whitney Cranshaw, Colorado State University,

Sort carrots before sale and storage for aster yellows symptoms, again, to avoid bitter carrots (and customers).

Small spots of a cercospora infection. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo,

For beets (as well as chard and potentially spinach), cercospora leaf spot is a somewhat common foliar disease issue.  Cercospora causes numerous circular spots on the leaf, which have red border and pale centers.  As the disease develops, these spots come together and can cause entire leaves to wither, which will hurt beet yield.  During the season, limiting periods of leaf wetness through drip irrigation or strategic timing of overhead irrigation can slow the disease’s spread.  A couple of lesions can produce hundreds  of spores that can live in the soil for 2 years, so crop residue destruction, volunteer and weed management, and rotation are key tools in continued management.  For more information, see this handout from Cornell.

Print Friendly and PDF