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Becky Weeks - Mar 7, 2021

The Best Kept Secret about Growing Carrots

Excitement rushed over me as stood in front of the giant vegetable seed display at our local hardware store, imagining all of the vegetables I could grow in my very first garden.  I gathered up some packets of our favorite vegetables: green beans, cucumbers, lettuce, peas, zucchini, carrots, and of course, tomatoes and headed home to plan out our new garden.  Once the weather had warmed soil was dry enough to till, we quickly got the garden prepped and I got to work planting my vegetable seeds. 

Over the next week or so, I watched with excitement as they all sprouted.  Well, all but the carrots.  They never seemed to do anything.  I tried to be patient, keeping them weeded and watered, but even after a month, there was no sign of life.  I finally gave up and decided to just be content with my other gardening successes.  Over the next few years, I attempted carrots a few more times, but never with great success until one day I discovered the secret, buried within the pages of a gardening book.  I decided to give them one more try and this time, I was amazed with the results.  I have used this method every year since and it has never failed me.  And ever since, I have been on a mission to spread the word about this awesome gardening secret.

The secret to growing carrots

So what was this secret that I found buried in that book?  The one trick that has had me growing great carrots every year since, no matter the weather?  Okay no more teasing.  The secret to growing great carrots is...radishes!

Lest you think that I have the attention span of a toddler, that was not a typo.  Radishes are indeed the world's best kept secret to getting your carrots off to a great start, at least in my opinion.  In this article, I'm going to discuss why this is, and how you too can use them to your advantage, all while saving precious garden space.  But before we get into discussing carrots and radishes and why they will forever be best friends in my garden, it's important to understand a few of the challenges gardeners face when growing carrots.

The challenge

The biggest challenge when starting carrot seeds is keeping the soil moist during the long germination period (up to 3 weeks).  Carrot seeds are very small and therefore they must be planted near the surface of the soil, where drying is most common.  You must be diligent about watering every day or so if rain is not frequent at that time.  If germination gets started and then the soil dries out one hot afternoon, it will be too late.  The fragile seedlings will be lost.  

On the other hand, frequent watering that produces large droplets, such as from a watering can or sprinkler, is likely to cause a crust to form on the top of the soil, particularly if your soil is a bit low in organic matter.  The small carrot seedlings have difficulty penetrating this soil crust.  If you do see them emerge from crusty soil, it usually is from within the cracks.  Soil crusting can be prevented by using a mister or drip irrigation, however in our climate, pretty much any 3-week stretch in the spring is guaranteed at least one pounding rain that can quickly cause crust formation.

The final challenge in starting carrots is keeping the weeds down.  It is often hard to know exactly where your row is within the weedy jungle that forms during those 2-3 weeks, which means that you are probably going to be on your knees pulling weeds, rather than using your hoe.  I have tried tricks to mark out the row, like using sand or chalk dust, but even so, the marker can fade if you get any particularly hard rains.

The solution

This is where radishes come in.  Radishes germinate quickly, usually in just 3-5 days.  Almost immediately, they put out a canopy of durable foliage that protects the ground from hard rain, keeping the soil surface soft.  And in as few as 3 weeks, they're done, ready to be harvested.  Do you see where I'm going?  That's right, the key to growing carrots is to interplant them with radishes!

I know, it's going to feel strange planting two different vegetables into the same row--usually, that is only done by mistake.  But I promise, once you try this you will love it.  In fact, I've gotten to the point where I almost never plant radishes without planting carrots, and I never, ever plant carrots without some radishes as companions.  

Why it works

When you plant carrots and radishes together-- in the same row, at the same time-- the most common carrot problems are solved.  Within a few days of planting, the radishes emerge, marking out the row.  Within a week, the radish leaves have formed a canopy that protects the soil from hard rain and keeps the surface consistently moist by shading it from the sun.  About 2-3 weeks in, the carrot seedlings begin to emerge from the soft, moist soil beneath the radish canopy.  And by the time most have germinated, the radishes are ready to harvest!  Since the radish root system is shallow and fairly weak, you can easily pull them from the soil, leaving the newly-emerged carrot seedlings undisturbed.  The voids left by the radishes help to aerate and loosen the soil, which is exactly what the carrots are going to need.  It's a perfect relationship!

How to interplant carrots with radishes

Growing radishes and carrots together couldn't be easier.  In fact, it's less work than growing them separate since you only have to mark out one row...oh and you only have to weed one row, which is even better.  Below is a step-by-step guide help you get started using this great trick for starting carrots.

1. Make a furrow

I use wide raised beds and plant carrots in short, perpendicular rows, so for me the easiest way to make a furrow is by pressing the handle of my hoe into the soil.  If you are using long rows, you can also drag the corner of the hoe in the soil to make a furrow, just as you would for anything else.

2. Mix the carrot seeds with a bit of soil

Using a small container (I use a coffee can, but anything will work) mix the carrot seeds in with a bit of soil.  I use about a half-pint of soil per packet of carrot seeds.  Be sure to mix very thoroughly.

3. Sprinkle the seed/soil mixture into the furrows 

Gently shake the seed mixture into the furrow you prepared.  I generally can plant about 12' of row with a half-pint of soil/seed mix.  That comes out to about one seed every inch, which is about perfect.  Then I usually second guess myself (it never looks like enough seed) and go back and sow more.  Save yourself the trouble and skip this last step.  It always ends in more thinning.

4. Sow the radish seeds

I know it seems weird, but go ahead and plant the radish seeds right on top of the carrots you just sowed.  Space them 1-2" apart.  You don't want to have to thin them any more than necessary.

5. Close the furrow

Place your thumb and fingers on either side of the furrow and pinch to pull the soil into the furrow.  This will keep your seeds in place and give just the right amount of soil on top of the seeds.

6. Water and wait

You don't need to water them any more often than the rest of your garden (about an inch per week).  Within a few days you should see radish sprouts.  If you see any weeds coming up, try to get them while they're small.

7. Harvest the radishes

After about three weeks you can start harvesting the radishes.  They should pull out without much trouble.  Some of the carrot seedlings may lean or fall over once you pull the radishes.  Don't worry, they'll be fine. 

8. Thin the carrot seedlings

This is what the carrot seedlings look like after the radishes have been pulled.  I usually wait a few more weeks to thin them to their final stand.  When you're ready, thin the carrots to one plant every 3-4 inches.

9. Water, weed, wait

Give the growing carrots average moisture and be sure to keep the row weeded.  Otherwise, I don't do much to my carrot beds.  Some gardeners choose to fertilize with a low-nitrogen fertilizer several weeks after planting.  I test and amend my soil each fall, so I don't do much fertilization in the spring.

10. Harvest the carrots!

Depending on the variety, you should be able to begin harvesting carrots around two months after planting.  Don't let them go too long since some varieties will begin to crack if they get too big.  That's it!  You conquered some of the most common challenges to growing carrots, all with less work and a bonus harvest of radishes in the middle.  Congrats!

Other considerations:

The method described above has produced great carrots for me year after year.  However, there are a few more things to consider before you get planting.

Bed preparation is key

Carrots that are grown in rocky dense soils will produce deformed roots.  Therefore, it is always a good idea to give a bit of extra attention to the carrot bed in the spring.  Ensure the the soil is deep, loose, and free of rocks or large clumps of soil.  Using a garden fork to loosen the deepest soil of the bed will produce uniform roots that can are less prone to breakage during harvest. 

Use early-maturing radishes

Interplanting works best when using early-maturing radishes.  Most spring radishes mature within 3-4 weeks and therefore make great candidates, however I would avoid using daikons, or winter radishes, which take too long to mature.  You want to be able to harvest the radishes as soon as the carrots have germinated, thereby giving the carrot seedlings unfettered access to water, nutrients, and sunlight.

Keep the bed well-weeded

Keeping the row well-weeded is essential.  Carrot seedlings are fragile, so if you let the weeds get too big, the seedlings will be damaged when the weed's roots are pulled.  Competition with weeds also can cause the roots to become deformed as they navigate the crowded soil space.

Fertilize as needed

Carrots are relatively low-demand in terms of their fertility requirements.  However, if you have very poor soil, you can amend the soil prior to planting or apply a low-nitrogen, high-potassium fertilizer several weeks after planting.  Avoid supplying plants with too much nitrogen as this will encourage top growth at the expense of roots.

Harvest carefully

When harvesting carrots, I plunge a potato fork as deeply as possible, right next to the row and then use it to lift the soil beneath the carrots as I pull on the tops.  This way, I rarely have problems with the roots breaking.

In Summary: The secret to growing great carrots

Interplanting radishes with carrots is a great way to get fragile carrot seedlings off to a great start.  This method solves the most common problems encountered when starting carrots.  The radish seeds germinate quickly, marking out the row, and their fast-growing canopy shades and protects the soil until the carrots have had a chance to germinate.  Finally, harvesting the radishes leaves the soil loose and aerated, creating a better environment for the developing carrot roots.  This method works well not only for carrots, but also for other slow-germinating seeds like parsley and parsnips and small, slow-growing seedlings like beets and chard.

Becky Weeks, Ph.D.

Geneticist, Gardener, Founder of Thresh Seed Co.

Becky is a geneticist with a passion for gardening. Prior to starting Thresh Seed Co., she spent fifteen years researching plant genetics and development, later applying those principles to aid in the breeding of commercial corn and soybean varieties. She lives on a farm in Iowa with her husband and two children, where she enjoys growing just about anything and experimenting with the breeding of new vegetable varieties.

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