Saturday, January 7, 2012

Garden Blog Series: How To Grow Carrots


Types of Carrots to Grow
Carrots are categorized into groups depending on shape and how deep they grow. I list a few common ones below.

Imperator: Thin, deep growing carrots of up to 10 inches

Danvers: These grow up to 7 inches long.  The tops are thicker and the flavor of the Danvers tends to be strong.

Nantes: These are sweet, round carrots that grow to around 6 inches long.

Chantenay: These grow around 5 to 6 inches. They are medium sized stocky roots which are more conical and have a good core and flesh color. Many consider these to be the tastiest of the carrots.

Purple, white and reddish varieties are also available on the market. I think the orange carrots are the best tasting ones though.

When to Grow
Carrots like cool weather, so you can sow as early in the spring as the soil warms up  (10C or 50F) and continue seeding them every six weeks until the fall. Usually, the last time you can sow them is about two weeks before the first expected frost date. You can start them earlier if you use a cold frame or row cover to cover them. Set up the row cover a few weeks before planting seed to warm up the soil.

Soil Preparation
Carrots grow best in a deep, loose soil that retains moisture yet is well drained. Carrots like loose, loamy, sandy, well weeded, well drained, soil. They grow great in sandy, soil with lots of organic matter. They do not like too much nitrogen in the soil so do not add manure or other high nitrogen fertilizer prior to planting. Even excess compost has caused my carrots to form multiple roots. The best soil pH is 6.5 - (5.5-6.8 will do.)

Sowing
You can sow your seeds after the last hard frost. Sow seeds directly in the ground and then thin. They can be planted about 3/8 inch into the soil The thinning distance is based on how big you want them to be when you harvest them. Will you harvest them when they are small or let them grow larger. Some folks like to have rows of carrots with some space between the rows. Other people like to grow them in large blocks quite close to each other. As long as you have good soil either way works fine. Give them enough room so they can get as big as you want at harvest time and don’t forget to leave room for you to get your fingers around them while pulling them out. This means you should usually thin them to about 3-4 inches between each one usually. If you have them overcrowded they will twist around each other from lack of room. They will taste good but look odd.

 Generally carrots are seeded and not transplanted. You can transplant them but transplanted carrots tend to fork.

Soil temp of 10c (50F) is good for germination. At this temp it usually takes 10 days for the seed to germinate.

Plant every 6 weeks or so for continual carrot harvest.

Watering
Light watering often promotes shallow root development and can increase the crop's susceptibility to hot weather and drought stress. On most soils, watering once a week is sufficient. Very sandy soils may require more frequent watering.
Not enough water creates tough roots with feeder roots extending off them. Too much water can cause the root to split all along its length. This usually happens close to maturity.

What Not To Do
Do not plant in heavy, clay soils with lots of rocks.  Do not plant in compacted soil. Do not put fresh manure in soil where carrots will grow or use other types of nitrogen fertilizer prior to putting carrot seed in the soil or you will get forked carrots rather than straight carrots. Even too much compost has caused this problem for me.

Minerals
They require moderate to high levels of phosphorus and potassium. Phosphorus can be added as rock phosphate and potassium can be added as ashes from your wood stove if you have one. Don't over ash though just because you have a lot of ashes. If the soil is too acidic lime can also be added. Carrots grow poorly in soil with high amounts of sodium. It is always helpful to get a mineral analysis of the soil in your garden before adding minerals.

Why My Carrots Look Odd
Forked roots: May be due to rocky or stoney soil or heavy, lumpy soil. Transplanting of long-rooted vegetables will also lead to forked roots. Too much nitrogen will cause the carrots to become forked too. 

Hairy, Tough Roots: If carrots don’t have enough water, the main root will form small feeder roots to soak up more moisture. They also form extra tissue to help carry the water. This extra tissue makes them tough. 

Small hairs all over the root: This is often due to an excess of fertilizer.

Split Carrots: Carrots can split along their entire length when there is too much moisture. This usually happens close to maturity.

Green Shoulders: This is due to the top of the carrot sticking out of the ground. It turns green when it is exposed to the sun. They can be exposed due to heavy rains washing soil away or the carrot pushing itself upward out of the soil.  The green part is not dangerous but will taste bitter so cut it off. 

Twisted Carrots: They did not have enough room and the roost twisted around each other. Give them more space next time. They may have run into rocks too.

Leaves Turn Yellow & Die: Aster Yellow Disease – A bacterial disease that causes young inner leaves of carrots to yellow and later form dwarfed leaf clusters. Slightly affected plants may still be edible. The roots usually bulge at the crown, are stunted and have many hairy secondary roots. Leafhopper insects spread this disease, so the best control is prevention of them. Cover vulnerable carrot plants with row cover right after sowing the seed. Certain carrot varieties, such as Scarlet Nantes and Royal Chantenay, are somewhat resistant to aster yellows.

Harvest
They can be harvested about 50-90 days after planting depending on how big you want them to be. Carrots are usually harvested when the roots are ¾ inches in diameter at the upper end, but you can harvest them any time they reach a usable size. If the soil is nice and loose you may be able to pull them out easily with your hands. If not,  loosen the soil around the carrot first, be careful not to break the root while pulling it.

Storage After Harvest
Wash them, let the moisture dry off so they are not wet, but quickly get them in the bottom of your refrigerator in a plastic bag. If you store them somewhere else, make sure they are close to 32 degrees farenheit and keep the humidity high.  You can also dig outdoor pits to store through the winter or buckets filled with sand that are left in root cellars, basements or I even store such buckets in my barn in the winter. I only wash them if I am storing them in my refrigerator. I don’t wash them if storing them in a bucket of sand or outdoor pit.

Disease & Pests

Carrot Rust Fly
Carrot Rust Fly (CRF) - (Psila rosae) is the main pest that I have had to deal with. I don’t have any other problems growing carrots as a general rule. The largest carrot growing region in the United States is in Washington State and CRF is the number one problem they deal with there. A couple other pests of carrots are the Aster Leafhopper and the Carrot Weevil. Since CRF is a large problem here, I will tell you a lot about it.

Besides carrots, the CRF also attacks other garden plants including parsnips, celery, celeriac, and parsley. The CRF larva(maggots) damage plants by eating small roots and by tunneling in larger roots. A rust-colored material develops in the tunnels, giving the insect its name. The infected plants may become yellow, stunted, and die. Usually the plant tops continue to look healthy. The larva often continue to feed in stored carrots. Disease organisms may enter the feeding tunnels and cause the root to rot.

The CRF flies into the garden or field of carrots to lay eggs at the base of the carrot.  Then they leave the area. Three – ten days later the eggs hatch into larva and move into the soil and feed on the carrot. They migrate down through the soil along the carrot root and penetrate the carrot as they feed. Larva feeding results in tunnels along the surface of the carrot and rust colored frass. The larva will eventually pupate in the soil. When the adult fly emerges from the pupal case, it flies back to the edge of the garden or field.

You will not know you have CRF damage until you lift a carrot at harvest time. Then you will see the dark colored tunnels in the carrot. If you have a really bad infestation you might notice the carrot leaves turning a orange or rusty color followed by a yellow color.

What Do They Look Like & When are They a Problem

The adult fly is 1/5 inch (5-6 mm) long and has a dark, shiny body with straw-yellow legs and head and large red eyes. In the Pacific NW the CRF lays eggs in May and June on the soil surface around the plants. The eggs hatch in a 3-10 days and the larva feed on and in the roots. The maggots are yellowish white and reach about 1/3 inch (8 mm) in length. They feed about a month and then change into brown pupa about 1/5 inch (5 mm) long. The pupa stay in the soil near the roots until August when the adult flies emerge. The adult carrot rust fly is a slender, shiny, black fly, about 6 mm long, with a small but characteristic reddish head and long yellow legs. The new flies lay more eggs which change to larva. This group causes plant damage into the fall. Some flies may develop in the fall. These insects spend the winter as pupa in the soil or as larva in the roots.  Larva from the August-September generation cause the greatest damage. Damage generally increases the longer the carrots are left in the ground.

What Conditions Favor CRF
• A previous history of rust fly infestations.
• Consecutive annual plantings of carrots in the same spot.
• Fields surrounded by brush and woods.
• Soils with high organic matter content.
• Lots of CRF weed hosts in area.

Management of Carrot Rust Fly

Monitoring
Carrot rust fly adults can be monitored with orange/yellow sticky traps placed in the carrot field or in nearby trees where the adults rest.

Identify and Remove weed hosts
Other Apiaceae or carrot family plants can host the flies. They include common garden veggies such as parsnips, celery, celeriac, and parsley. They also include herbs or weeds such as dill, coriander, wild carrot, lovage, fennel, parsley and all the other Apiaceae family members.

Plant Late
Avoid early-season egg laying by planting after early adults have emerged and dispersed. Mid to late June is a good time in my area to plant and avoid the flies. However if you have neighbors with carrots or other alternate plant hosts are in your garden this won’t work.

CRF Are Attracted to the Scent of the Carrots
The CRF is attracted to a chemical that the carrots produce when they are under environmental stress. Even weeding the carrots and moving the leaves around may release more of this scent and attract the flies. So weed when there is no wind so the scent does not travel far or weed in the evening when the sun is going down as the fly takes air only in bright sunlight. Pulling the carrots in the evening is also helpful for this same reason.

Confuse the Flies with Strong Smelling Herbs
Some folks have good results putting strong smelling dry herbs around the base of the carrots such as pennyroyal, rosemary, sage and wormwood. Since they lay eggs at the base of the carrots covering the soil with a strong smelling herb will both confuse them and cover the soil where they would usually lay eggs. Some people also plant between row crops of strong smelling herbs.


Cover Crops Planted Between Carrot Rows Can Also Confuse them
Growing the carrots with cover crops between them has been an effective solution to keep the CRF from finding them. Some cover crops that have been used are Crimson Clover, Medic, Subterranean Clover, Vetch and White Clover.  Additionally, they help enrich the soil. These crops enhance the soil and provide cover for beneficial insects. It is thought that they help hide the smell of the carrots and confuse the flies.

Row Crop Covers Can Be a Physical Barrier to the Flies
Covering the carrots with a floating row cover works for garden growers but is hard for people who have large fields of carrots. Seal them well at the soil line. Be sure you do not have maggots or pupae in the soil where you place the row cover though. Never grow carrots on a soil area that was infested with rust fly the previous year.  Carrots and other Apiaceae family members should never be planted in the same area as the prior year.

Raising the Carrots more than 18 inches off the Ground
Since CRF usually flies no more than 18 inches above the ground, some folks have grown them in raised beds above this height. Here is a video of one such method.

Rotate Crop
They are weak flyers, they tend to stay localized. They are thought to travel less than 1000 yards in search of egg laying sites. They are atracted to host crops and fly upwind towards the smell. Isolation of your crop from last years field or garden area can reduce risk. Not every gardener has the space to move their crop that far though. This works better on a farm.

Clean Up
Discarded piles of overwintered carrots or parsnips can be a source of flies and should be removed. Leaving your carrots   or parsnips in the soil over the winter is also a place they can hibernate until spring. 

Mulch Them or Apply Ashes
Mulching with grass cuttings/straw or applying diatomaceous earth or wood stove ashes around them can make it harder for the female flies to find a good egg laying site. If you mulch be aware that slugs and snails like to live in mulched areas.

Beating the Carrot Root Fly

Birds
Birds and chickens serve as excellent biological controls in fallow ground where pupae are suspected. If you can put your chickens in the garden without causing damage (Chickens scratch up bugs from the ground, so if you don't want them damaging roots, be careful where you put them.) they will help clean up many bugs.

When You Have the Fly in Your Carrots Harvest Early and Don’t Provide them With A Place to Eat

Early fall harvesting and storage of carrots in pits and root cellars rather than in the ground help minimize fall infestations caused by late second or early third generation larva. 

Get rid of these carrots quickly. Do not store buggy carrots in the ground through the winter. If they are still worth saving, harvest them and put them in cold storage where larva can’t get back into the soil. The larva still in the soil is starved to death as long as there are no other carrot family plants around. Carrots with worms can still feed your animals.  I give them to my goats. You may have an animal who might enjoy them too. I feed all wormy garden produce to farm animals to remove the worms from my farm.

What Non-Organic Folks Do (Don’t do this at home kids!)
Non-organic folks use insecticides even though they have limited effectiveness against CRF. This is due to the fact that the adult rust fly spends most of its time on the periphery of your garden or field. They fly into the garden or field to lay eggs and then leave the area. After the larva hatch they move into the soil and feed on the carrot. It eventually will pupate in the soil. When the adult fly emerges from the pupal case, it flies back to the edge of the garden or field. Many types of pyrethroids and organophosphates have been tested to kill or control CRF. It has been found that the pyrethroids do not appear effective against eggs and larvae , but do decrease adult populations with continual broadcast spraying. This also kills all the beneficial insects and even the non-organic folks usually realize this type of constant over-spraying is hazardous to the end user of the carrot. Some organophosphates have been effective against the larval stage and the recommended pesticide for control of CRF in the Pacific NW is to use Diazinon at the time of planting the seed as a seed furrow drench. I don’t know about you but I don’t want to eat any carrots that had their seed drenched in Diazinon. There is a good chance if you eat non-organic market carrots that your carrot was grown in a Diazinon drenched garden. So if you buy carrots, only buy organic ones.


Carrot Weevil
The carrot weevil adult is a dark-brown snout beetle about 6 mm long.  It over-winters in plant debris in and about carrot plantings that were infested the previous year.

In the spring, adults become active and mate after a few warm days. They are capable of laying eggs by mid- to late May. However, they do not attack the new crop of carrots until the first true leaf stage. Adult females chew small cavities in the crown of the carrots and deposit two to three eggs in each cavity. They seal the cavity with a black exudate. Eggs hatch after one to two weeks and the young larvae tunnel down into the root or leave the stalk and enter the roots from the soil. Some young plants may wilt and die as the slender root is tunnelled by the developing larva. The damage is not otherwise conspicuous until the larva are nearly mature.

After feeding for at least three weeks, larvae leave the carrot and pupate in the soil. After one to two weeks, adults emerge. If warm weather or an early carrot crop has permitted the adults to mature early enough in the summer, some second-generation eggs and larvae may occur.  In warm areas second-generation injury is more common.

Management of Carrot Weevil
Monitoring the activity of carrot weevil adults is an effective means of determining the level of weevils. Wooden-plate or carrot-root sections placed in the soil can be used to monitor adult activity, starting at the time of seeding. 

Carrot weevil adults rarely fly and therefore the insect does not spread rapidly. Its presence in a particular location should be evident for a season or two before it builds up to serious levels. Development of a serious infestation can be delayed by not planting carrots on or adjacent to sites that were infested the preceding year.

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