When to Plant Tomatoes (Don’t Make this Common Mistake)

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Tomatoes will experience severe injury or die when the temperature drops below freezing, 32ºF or 0ºC. Therefore, the best time to plant tomatoes is after the danger of frost has passed in your area. It’s a simple concept but there is so much more to it than meets the eye. If you want to know when to plant tomatoes there are other important things to know.

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Find Out your Average Last Frost Date

My favorite average first and last frost date finder by zip code can be found HERE. One thing you may not realize when you search by zip code and see two very exact dates is that these dates are based on the averages of the last 30 years of data. 

What’s more is you need to realize that the exact first and last frost date are based on a probability level of anywhere from 30-50%. For example, based on the website I reference above, my average last frost is April 19th and my average first frost is October 13th. 

Since it is an average, the probability of our area getting a 32ºF frost on April 19th is 50% or a 50-50 chance. By May 4th, the probability drops to 10%. 

Find Out How Many Frost Free Days You Have in A Year

The next step is to find out how many frost free days you have in a year. Using the same website I linked above, it states for my area,  “You have at least 176 freeze-free days in a year.” 

The reason it’s important to note this is because some growing seasons vary based on climate. My in-laws who live in Idaho have 84 freeze free days in a year! It takes 80 days for a Roma tomato to come to maturity. I have a list of the best tomatoes for a short growing season HERE.

I will explain more on how this number affects when to plant tomatoes below.

Check the Weather

Once you know your average last frost date and how many frost free days you have in a year, check the weather forecast. Usually, you can see 14 days in advance and get an idea of if there is a cold front coming and if there is frost in the forecast.

When to Plant Tomatoes in Long Growing Seasons (170+ Frost Free Days)

If you are in a climate with a long growing season of many frost free days, I recommend planting two weeks after your average last frost. The probability of a frost becomes lower and there is less risk. 

Another reason to wait a couple extra weeks to plant is because spring is the time of thunderstorms and hail. Frost can kill tomatoes but so can severe winds, flooding, and hail. The probability of severe weather, especially for those east of the Rocky Mountains in the US, goes down the closer it gets to summer. 

Another consideration for very long growing seasons in areas that get very hot in summer is to plant with the intention to harvest before 100ºF + days and over 75ºF nights. 

My Mom and Step Dad live in south Texas and plant two weeks past their average last frost date but no later. The reason for planting right on time is because if they wait any longer the high heat of summer will make the blossoms fall off the tomatoes and they don’t produce well. 

When to Plant Tomatoes in Average Growing Seasons (120-170 Frost Free Days)

If you live in an area with a growing season in this range, plant tomatoes 1-2 weeks past your last average frost date. Also consider growing tomatoes that mature in less than 100 days.

Another consideration if you have the means would be setting up a hoop house, high tunnel, or greenhouse. The extra protection will help you to be able to get tomatoes to maturity quickly. 

When to Plant Tomatoes in Short Growing Seasons (Less than 120 Frost Free Days)

If you have a short growing season, I understand the need to plant as early as possible. We lived in an area with 84 frost free days. If you don’t plant right away you may not get a harvest at all because the season is so short.

For cool and short growing seasons, there isn’t enough time to wait the extra two weeks I’d normally recommend. Wait until your average last frost has passed and check the weather before planting. I also have some ideas of alternative things you can do.

How to get a jump on growing tomato plants in a cold area:

1. Start tomato seeds indoors and transplant them
2. Two to three weeks prior to planting add black compost, black ground cover, or black plastic on the area where you will plant the tomatoes. This will heat up the soil significantly and help a lot for those with cold nights. Leaving it in place throughout the growing season will also help the tomatoes to grow faster.
3. Transplant tomatoes, then cover the area with a low tunnel. A low tunnel is an area you make with support hoops and row cover. When the tomatoes are small they will fit under the tunnel with no problem and it will stay warm enough even if there is a light frost. I really like simple wires used as hoops found HERE and row cover can be purchased HERE by searching for “Frost Cover”. I usually get 1oz fabric frost cover for more protection.
4. Use a high tunnel or greenhouse. If you are in a cold climate, do whatever you can to get a greenhouse or high tunnel. The investment will pay itself off very quickly with the ability it gives you to extend your growing season, raise the outdoor air temperature, and get a much bigger harvest.
5. Use both low tunnels and a high tunnel. If you have an unheated space, using a combination of both low tunnels and a high tunnel will give extra protection against frost, heat your tomatoes, and heat your soil. These are all wins in a cold climate!
6. Plant varieties of tomatoes that mature quickly. Usually determinate tomatoes are best since they ripen all at once. I have a list of tomatoes and best plants for short growing seasons HERE.

The Common Mistake

The common mistake is to plant too early. Every single year, I have people I associate with tell me they had their tomatoes all die because of frost or get severely damaged due to a spring storm. While not all weather is predictable, there are weather records and you can understand the probability of a frost. 

Even this year, some friends of ours had a devastating loss of tomato and pepper plants due to a frost. It was still March, one month before the average last frost date. The probability of a frost happening between that time and summer is 90+%. 

They planted all the heat loving plants that early because they have a hoop house. As such, they figured the frost wouldn’t be cold enough to affect the plants within that space. Since the hoop house is unheated all the plants froze. Both Cam and I were so devastated for them! We know how much work and time went into those plants. 

You don’t always have to learn the hard way, just be patient and it will pay off!

Other Considerations of When to Plant Tomatoes

As I mentioned above, when to plant tomatoes is not as cut and dry as it seems. There are other considerations at play that may need to be considered if they apply to you. Some of those considerations are whether you are transplanting or direct sowing tomatoes. Other considerations include planting in an unheated tunnel or a heated greenhouse.

Transplanting vs Direct Sown Tomatoes

It isn’t very common for gardeners to directly sow a tomato seed in the soil. However, it can be done successfully. On most tomato seed packets, days to maturity means the average number of days it takes after a tomato is transplanted to get ripe fruit. 

Therefore, a tomato seed that is directly sown will likely require more days to get to maturity. It will require more days because it hasn’t already been started.

If you choose to direct sow your tomatoes, they can be planted at your average last frost date. I recommend this because tomatoes will wait and sprout when the temperature is right. Direct sowing is a more foolproof method because soil temperature dictates when it is the right time to germinate.

A long season is necessary if you plan to direct sow tomato seeds.

When to Plant Tomatoes in an Unheated High Tunnel or Caterpillar Tunnel

Planting tomatoes under the protection of a tunnel can provide a slight amount of added protection against frost, wind, and hail. 

An unheated tunnel varies in how much it buffers against frost and stays above freezing. There is variation in temperatures of individual tunnels due to materials, insulation, what floor material is used. Some tunnels are made to be completely sealed and others may have gaps that allow air flow.

Due to so much variation, there is no way for me to put out a formula of exactly when to plant. Put a thermometer in your tunnel and closely watch the differences between outdoor temperatures and the temperature inside the tunnel. With time, you’ll be able to make your own safe predictions on when to plant. 

When to Plant Tomatoes in a Heated Greenhouse

A common misconception about using a heated greenhouse is that you can plant anything at anytime. This is not true!

This is mostly due to the need for light. If planting tomatoes in the dead of winter in New England for example, even with supplemental heat they will not thrive. They will not thrive because they need lots of light and lots of heat. For most the cost of heating would outweigh the worth of the tomato.

Can Tomatoes Live through a Frost?

If you’ve heard stories of tomatoes going through a frost and surviving, that has to do with the duration and temperature of the frost. A light and very brief frost 32-34ºF may only cause injury to the plants. On the other hand, a hard frost (below 28ºF)  that lasts several hours is almost certainly a death sentence to uncovered tomato plants. 

When to Plant Tomatoes | Summary

Here are the steps to help you know the best time to plant tomatoes:

1. Find Out your Average Last Frost Date
2. Determine How Many Frost Free Days You Have in A Year
3. Check the Weather
4. Adjust planting time of tomatoes based on the number of frost free days per year.
5. Avoid the most common mistake at all costs!

Also adjust your timing based on where the tomatoes are growing. Are they in a high tunnel, greenhouse, low tunnel, or other protected space? Will you be direct sowing or transplanting?

All these considerations must be taken into account to discover when the best time to plant tomatoes is for you.