Growing Tomatoes In Cold Climates & The Sub-Arctic

Garden Tips, Techniques


Growing outdoor tomatoes in the sub-arctic and Alaska is not impossible.  It’s actually quite possible to do, even without a greenhouse.  It does take some care to grow them outside, but you can have ripe tomatoes in time for that early first frost.

The techniques we discuss in this article are applicable to almost any cold climate out there.  You may need to slightly adjust times and dates based on your actual last frost dates.  If your growing season is in the three month range, these tips will apply.

Tomatoes are a tropical plant, they would never grow naturally up north if it weren’t for gardeners planting them.  Most tomatoes love warm summer days and better yet, still-warm evenings.  The interior of Alaska, and other areas between the 55th and 65th parallel, are surprisingly warm enough for the summer for growing tomatoes when you care for a few specific things.

1. Start With Good, Cold-Climate Tomato Genetics

Growing tomatoes in the sub-arctic and other cold climates starts with good genetics.  Fortunately, these days, many tomato varieties exist.  Some varieties are bred specifically for growing in cold climate areas.

Look For Traits, Not Varieties!

We’d like you to focus more on the traits that you’re looking for as opposed to specific varieties.  This will open up your options more than following exact variety lists.  Sure, take some hints from the “pros” and grow what they tell you works well, but don’t be afraid to try something different.  There are many vendors out there who sell tomato seeds specifically marketed towards cooler climates.

You should typically seek varieties that will mature in 75 days or less, to offer enough time for ripening.  You may also see them called “early” varieties, which means that they will mature earlier than most.

We’ve seen a number of Russian/Siberian, Canadian and eastern European varieties that are suitable for our climate.  They can be indeterminate or determinate varieties, both types will work with our imminent and unforgiving early first frost.  Most tomatoes that will be well off here in the extreme north tend to be smaller varieties as well.  Not just cherry tomatoes, but other varieties that grow to 2-3 inches.  That’s not to say you can’t grow a one pound whopper up here.  You probably can.  It just might be green when you pick it.

Examples Of Cold Climate Tomato Genetics

There are many varieties that are specially bred for cold climates and the Alaskan outdoors.  Some examples of these varieties are:

  • Stupice (pronounced stoo-peach-ka)
  • Polar Beauty
  • Alaska
  • Sub Arctic
  • Glacier
  • Early Tanana
  • Polar Star
  • Beaverlodge
  • Manitoba
  • Azoychka
  • Thessanoliki
  • Moscow
  • Purple Russian
  • Most cherry tomato varieties have produced well for us
  • Check out the UAF Extension service variety list for other varieties that have been tested in Interior Alaska.

Your local nurseries will likely sell tomato starts that are going to do well in your area.  They have every incentive to get you to come back next year.  It might be wise to avoid “big box stores” and such, at least that’s been our experience in Alaska.  They often get varieties that might do well “in the north” but not necessarily the extreme north.

If you have a greenhouse, especially if it’s heated, your options are a lot more diverse.  With these, you could look at 80+ day tomatoes, including some prize-winning heirloom varieties.  Early varieties are still going to be a good bet, though.  You will have superior results if you can heat your greenhouse into the early fall as that’s prime ripening time.  For some readers, though, that’s just not an option and this piece is written for them.

2.  Diversify Your Tomato Crop

A great piece of advice we’ve learned over the years is to diversify your crop.  Don’t grow just one kind of tomato, grow several different kinds if you can.  Different weather patterns could adversely affect one variety and if all your eggs are in one basket, you could lose your entire crop.  We’ve had years where one variety didn’t produce well and others have.  Growing several different varieties not only will guarantee more choice, it will also protect you against single crop failure.  There are no issues with growing multiple types of tomatoes side by side, such as with cross-pollination.

We usually test a new variety every year as we want to learn for ourselves what does and doesn’t work.  But, if a variety doesn’t do well over a couple of seasons, we don’t bother growing it.  Some varieties just can’t handle our cooler evening temperatures and won’t produce in our cooler environment.

3.  Get An Early Start On Your Tomato Crop

It really isn’t practical to grow tomatoes from seed entirely outdoors in cold climates.  The season just isn’t long enough to allow the plant to fully mature and produce a good crop.  A successful bounty of tomatoes will require you to start your seedlings indoors or purchase starts from a nursery.

Tomato seeds will germinate best in warmer soils.  Try to aim for above 65 degrees Fahrenheit and preferably over 70 degrees.  Tomato seeds will be finicky, at best, in cool soils.

Tomato Planting Schedule

If you intend to grow your tomatoes outdoors, plan on planting those seeds 6-8 weeks before last frost.  (In the interior of Alaska, last frost is recognized as June 1st.)  If you have space and lighting for larger indoor tomato starts, the earlier of those dates will result in more mature and better fruiting plants.  If you are cramped for indoor growing space, the later of the dates will still work in our northern environment.

For those that intend to grow tomatoes in a greenhouse, then you can start tomato seeds as early as 8-10 weeks before last frost.  This will allow you to transfer your tomatoes into your greenhouse 2-3 weeks prior to last frost, which for interior Alaska is about mid-May.

Some people plant their tomatoes very early.  We’ve seen people seeding their tomatoes 10-12 weeks before last frost.  To each their own, but you should know that will result in some very large tomato starts come April and May.  Just make sure you have a plan if you want to do this.

4.  Try To Pick The Warmest Spot For Growing Tomatoes

You want a site that will be as warm as possible during the day.  Tomatoes aren’t terribly fussy about the amount of daylight they receive, but aim for about 8 or more hours per day.  I honestly wouldn’t worry about that just below the arctic circle.  Sun equals warmth and we want as much as we can get.

You definitely want to avoid areas that are heavily shaded throughout the day.  If you are assessing areas for a tomato garden, your best places will be where the snow melts first during spring.  Chances are good that if snow tends to stick around in an area, the ground will be a bit too cool for tomatoes.  This will hamper your tomato growth.

This location for tomatoes has a lot of things going for it. It has stone insulating the plants from the ground.  It is also near the home, which will radiate heat. Dark colored containers are also a great way to provide extra soil warmth for tomatoes, which can be a major advantage in cooler climates.

5.  Keep Your Roots Warm

Remember that soil warms much less quickly than the air does.  While the ambient temperature may be well within a tomato’s preference, the soil underneath could take a lot longer to warm up to similar temperatures.

You will do well by picking an area with the warmest soil possible.  This may be a raised bed or even raising them as a container plant in a regular, fabric or sub irrigated pot.  Our side-by-side testing has shown that outdoor tomatoes do better in containers than any traditional ground based garden here.  If you are using containers, getting them off the ground will also help a lot.  Placing them on a deck or other raised structure will be warmer than the ground as well.  Black containers will absorb more heat, which is a good thing in cold climates.

Using mulch over the soil is a good practice for sub-arctic tomatoes, especially if you’re growing in the ground.  You can use black IRT (infrared transmitting) plastic, weed fabric or some other dark mulch.  This will help to trap the heat in the root zone, which is especially important for our cooler evenings.  The soil will warm up more quickly and release its heat more slowly than exposed soil will.

If you are growing in an area where permafrost is known to exist, you definitely need to get your plants off the ground.  Plan on either using an elevated raised bed (off the ground) or growing your tomatoes in containers.  There is no other way.

6.  Adjust Your Tomatoes To Outdoor Temperatures Gradually

Remember, tomatoes are a tropical plant.  They aren’t used to our cold summer nights.  The shock of going from indoor temperatures to a 38 degree night is enough to kill a young tomato plant.

If you can, while you are hardening off your plants, gradually introduce them to our outdoor evening temperatures.  As you are hardening off your plants, start with warmer days preferably over 50 degrees Fahrenheit.  As possible, gradually introduce them to cooler periods, such as in the evening.  If there are particularly warm evenings predicted (over 50 degrees Fahrenheit), you can leave them outside overnight if they’ve been sufficiently hardened off.  Eventually, they will take to the cooler weather and transplant to their final home will be easy on them.

We have had no problems with our tomatoes surviving even sub 40 degrees, but they were gradually introduced to those temperatures.  If it’s going to be colder than that at night, and you can’t bring them inside, you will want to use a frost cloth to protect your plants.  Especially if there is danger of frost.

7.  Feed Your Tomatoes Appropriately

Feeding your plants regularly is important.  Our vast periods of sunlight in the sub-arctic keeps our plants in constant overdrive.  Often times even a rich compost won’t be enough and you will need to supplement with additional plant food.

Tomatoes are a fairly hungry plant and will benefit from extra fertilization.  After germination, they will take well to nutrient rich soils with plenty of composted materials.

Once your plants have a couple sets of true leaves, feed them with a nitrogen rich fertilizer.  This will help them get big and strong so they can produce many tomatoes.  You can use most all-purpose fertilizers early in the plant’s life (pre-bloom), where nitrogen is the most important component.

Use A High Quality Tomato Focused Fertilizer

Once you have transplanted outdoors or to your greenhouse, you’ll want to switch your fertilizer to something focused on blooming and fruit production.  We really like Epsoma’s Organic Tomato-tone or JR Peter’s Tomato Feed for this purpose.  (Despite the name, these will also work well on other veggies too.)

Tomato specific fertilizers are a little different from normal “all purpose” fertilizers in that they contain calcium and magnesium, both of which tomatoes need.  This will make sure the tomatoes have a complete nutrition and will encourage them to produce blossoms.  Our fertilizer specifies every 7-14 days, we usually use the shorter end of that scale here.

Fertilize on the recommended schedules, but also keep an eye on the weather.  If you see a week or more of nice warm weather, fertilizing early in that cycle will allow it to take advantage of the heat and grow well.  Likewise, if rain or cooler temperatures are predicted, it might be better to hold off on fertilization until nice weather returns.

A little note about watering.  Tomatoes are sensitive to drought conditions, so you want to make sure they are continually watered.  This can be challenging in containers as the available water can get used up quickly.  You can look into sub irrigated containers or irrigation systems, which eases this concern significantly.  Also, remember that big rainfalls can leech fertilizer out of your soil, so maintain your fertilizer schedule.

8.  Manually Assist Your Tomatoes With Pollination

Even if you happen to have a bee hive next door to your tomatoes, it will not harm your tomatoes to assist with pollination.  Tomatoes are self pollinating, so they do not require pollen to travel from flower to flower.

All you have to do is gently tickle/shake/wiggle the tomato’s flower clusters.  We usually do this once every day or two as the flowers come into bloom.  This will knock pollen to where it needs to go and will more or less guarantee a tomato will grow there.  Manually assisting pollination will greatly enhance your production and your yields will be larger.

Some people use electronic toothbrushes and other gizmos for this.  Do whatever you think is right, but we’ve had great success by careful use of our fingers.

9.  If You Can, Use Poly Covers or Cheap Greenhouses To Trap Heat For Your Tomatoes

The focus of this post is outdoor tomatoes in the sub-arctic.  But, there’s no getting around that tomatoes like warmer conditions.  There are some relatively inexpensive options for creating a more suitable climate for your tomatoes.

It’s not very difficult to create a poly tunnel out of PVC and some clear poly tarp.  The tarp material can often be found at local nurseries and can also be purchased online.  There are lots of tutorials on-line about how to build a poly tunnel.  It doesn’t have to be a full greenhouse, just a few bends of PVC and a clear poly cover.  Just make sure you secure the structure in the event wind picks up.

Alternatively, there are relatively inexpensive plastic greenhouses that can be found at places like Amazon and local hardware stores.  They are often temporary and can be taken down for the winter.  Most of these won’t last more than a few seasons, but they are cheap enough and offer you flexibility you won’t have otherwise.

Both of these can be a double-edged sword and you need to be careful with them.  During the day, if there isn’t proper ventilation, you can easily produce plant killing temperatures.  Seriously, 130 degrees on a 60 degree day is not impossible and that will kill your tomato plants quickly.  Proper venting is critical.  You might also want to read our article on small greenhouses and temperature control.  Try to strike a balance between venting and heat retention.

10.  Prune Your Tomato Plants

There are two kinds of tomatoes, determinate and indeterminate.  You need to know what you are growing because they are pruned differently from one another.  A seed packet or research on the internet of your varieties is essential.

Indeterminate Pruning

With indeterminate tomatoes, you will need to learn about suckers.  This is a new stem that will form at the internodes, typically at a 45 degree angle to a leafed branch.  If left on the plant, it will turn into another main stem and your plant will soon be growing every which way.  Throughout the season, you should be trimming these off as much as possible to allow your plant to put energy into producing fruit and vertical growth.  We want the plant to focus on growing tall, not wide.  Tomato plants grown in the sub arctic will usually be smaller than those grown elsewhere anyway.

Also, if you are growing indeterminate varieties, about a month before the first frost, aggressively prune your foliage.  Be sure to leave the tomato clusters, but we do remove tomatoes that have no hope of getting larger and ripening in that last month.  Remove most of the lower leaves and branches late in the season, but still keep some so the plant can photosynthesize.  Pruning roughly the bottom half of the plant is a good goal, but you can do as much as 2/3’s of the plant. We even top the tomato (literally, cut the top off) about a month before first frost.  This will allow all produced energy to be put into fruit production and ripening.

Determinate Pruning

Determinate varieties will grow to a specific height (typically 4-6 feet) and then will stop growing larger.  For these, you don’t need to trim the suckers and the plant will only get so wide and so tall.  You can trim leaves or branches as needed, but in general you don’t have to do much with determinate varieties.

For both types, you will also want to trim all the leaves and branches from the bottom 6-12 inches of the plant.  A good rule of thumb is to trim all foliage up to the first flower cluster.  This will promote air circulation around the plant.  Good air circulation can ward off many problems before you get them.

11.  A Month Before First Frost Is The End of Flowering As You Know It!

Given the impending frost that is coming, there comes a point where you need to shift the plants growth from creating new tomatoes to finishing the ones it all ready has.  The best way to do this is to remove all of the existing flowers that do not yet have tomatoes.  Continue to be vigilant about maintaining suckers on indeterminate plants.  Continue doing this from a month before first frost until you fully harvest.

Removing the flowers will cause the plant to focus on maturing the fruit that exists.  This is very important in cold climates because we often see plant-killing frosts in September.  Any new fruit would not have an opportunity to mature anyway, so it’s important to help the plant focus on the fruit that is all ready growing.

With indeterminate varieties, it’s also not a bad idea to top the plant at the same time.  Just cut the top of the plant off and continue to maintain any suckers that are produced.  This again will cause the plant to put its energy into ripening fruit as opposed to getting even taller.

Bonus Sub Arctic Tip – Find Recipes For Green Tomatoes!

We’re sort of kidding, but really not.

No matter how good a gardener you are, chances are good you’re going to have a few green tomatoes at the end of the season.  We only have so much time and without September or October available for outdoor crops to mature, you’ll have to take what you can get.  The only way to get those extended seasons here in the sub arctic is through a fully heated greenhouse.

You can try to enclose your harvested tomatoes in paper bags, which will help them mature somewhat.  It’s not a miracle though.

Fortunately, there are literally tons of recipes for green tomatoes and many of them aren’t actually that bad.  You can find green salsa and other sauce like recipes that work really well with the green tomatoes.  Even canned green tomatoes are a nice little snack through the winter months.

In closing of this subject, we did find a storage tomato variety this year that was bred to mature off the vine.  It is an early producer and was never found on any variety list we’ve seen for Alaska.  (Remember what we said in tip #1?  Look for specific traits!)  This variety is an early producing storage tomato and can be stored for several months off the vine, during which time it will mature more fully.  These have produced well for us in Alaska and allow us to harvest them green while they mature over early winter.

We hope that you’ve found this focus article helpful and choose to raise some really awesome tomatoes.  If you’ve found some varieties that do really well in sub-arctic areas, we would love to hear about them.

4 comments… add one
  • Marieke Dec 31, 2019 Link Reply

    Thank you for this. We’re in the north of Scotland(UK), which is slightly milder than Alaska, most years 😉 The storage tomatoes were completely new to me, definitely trying those. Thanks again!

    • Jeff Feb 2, 2020 Link Reply

      You are welcome! We are glad that we could contribute to your garden and wish you the best of luck. We love our Golden Treasure storage tomatoes. We still have a couple dozen that are still in good condition, harvested in August and it’s now January!

  • Beth Bennett Apr 11, 2020 Link Reply

    Last year we grew a variety of tomato called Northern Lights. We aren’t the MOST successful tomato gardeners, but last year was our best year ever. And Northern Lights was a standout. In the seed catalog it said it was a large, bicolor 55 day heirloom tomato with great flavor. SO glad we tried it. They did as well or better outside as in the greenhouse. Planted seeds along with 7 others about 12 days ago, and they were the first ones up, and taller than any others, and starting to get true leaves. You should try them!

    • Jeff Apr 11, 2020 Link Reply

      That variety looks fantastic! I love the bi-color on the inside of the tomato as opposed to the more common skin variegation. I have put it on our buy list for 2021! Thanks for the tip, we’ll definitely try them out!

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