Temperature and Humidity – Page 2 – GreenUpside – Learn how to grow a green garden with us!

Maybe this is your first year planting tomatoes, or you just got busy and forgot to plant your garden. Either way, you don’t want to waste your time and effort planting if it is too late in the season. So, when is it too late to plant tomatoes? For spring planting, move tomatoes outdoors by late May or early June, sowing seeds indoors 8 weeks before transplant. In warmer climates, you may be able to plant a second tomato crop later in the season. If you are late to planting, try a fast-maturing tomato variety, such as Fourth of July. Of course, you can extend your growing season by starting seeds indoors in late winter to early spring, using a greenhouse during the season, or using row covers at the end of the season. If it really is too late to plant outdoors, you can dedicate some indoor space near a window for growing tomatoes in containers. In this article, we'll talk about when it is too late to plant tomatoes. We'll also look at how to calculate planting times based on days to maturity. Let's get started. When Is It Too Late to Plant Tomatoes? To determine whether it is too late to plant your tomatoes, you will need to look at two main factors: First Fall Frost Date (this will depend on where you live, and it can vary by year). Time To Maturity (this will depend on the tomato variety, and it can vary by several weeks). First fall frost date and time to maturity will help to determine if it is too late to plant tomatoes. Let's start by looking at frost dates. First Frost Date The first frost date in the fall is the day that you would first expect a frost (freezing temperatures of 32 degrees Fahrenheit or below). Usually, the first frost will come at night, when the sun is down and temperatures are lower. This is why you often see white frost on the grass in the morning when you wake up after a frost. You want to make sure your plants are mature and harvested before the first frost of the fall season! A frost will kill many unprotected plants. It can also damage the fruit on mature plants, and that includes tomatoes. So, make sure that your plants are mature and ready for harvest before the first frost date. The first frost date will depend on your location. It can vary quite a bit, depending on whether you live in Montpelier, Vermont (September 24) or Miami, Florida (frost is rare). To find first frost dates in the fall, check out this guide from the Old Farmer’s Almanac (they also have last frost dates in the spring). For example, if I type in the zip code “02150” (a Boston zip code), we get a first fall frost date of November 3. Note that these dates are probable first frost dates, using 30 years of data. In theory, you could still get a frost sooner than the first fall frost date! (You can learn more about what frost dates mean in my article here). Most of the time, tomatoes will mature before the first frost date if you plant early enough. If you live in a cold region with short summers, you should check the frost dates before planting. Time To Maturity For Tomato Plants The time to maturity for a particular variety of tomato is the time in days from seed to harvest. Together with the first frost date, the time to maturity can tell you the latest date you should plant your tomato seeds. Check the tomato seed packet to find the time to maturity (also called DTM, or days to maturity). The time to maturity can range from as little as 50 days (about 7 weeks!) to over 90 days (about 3 months). To find the time to maturity for your particular variety of tomato, check the seed package or the seed company website. The following tomato varieties have a short time to maturity: Bloody Butcher – this tomato variety is indeterminate, with 3 to 4 ounce fruit maturing in 55 days. You can check out the Might Sweet tomato variety at Burpee’s website. Fourth of July – this hybrid tomato variety is indeterminate, with 4 ounce fruit maturing in 49 days. You can check out the Fourth of July tomato variety at Burpee’s website. Mighty Sweet – this hybrid tomato variety of cherry tomato is determinate, with 2 ounce fruit maturing in 55 days. You can check out the Might Sweet tomato variety at Burpee’s website. Summer Girl – this hybrid tomato variety is highly resistant to disease, with 5 to 6 ounce fruit maturing in 49 to 52 days. You can check out the Summer Girl tomato variety at Burpee’s website. Umamin – this hybrid tomato variety is indeterminate, with 6 to 8 ounce fruit maturing in 60 to 65 days. You can check out the Umamin tomato variety at Burpee’s website. Taking frost date and time to maturity into account, you can figure out when to start your tomato plants to ensure that you avoid frost. Fast maturing tomato plants, such as Fourth of July, produce a harvest sooner at the expense of smaller fruit. When To Start Your Tomato Plants If you are in Zone 10 (parts of Hawaii, southern California and southern Florida), you can plant tomatoes late as a fall crop. Otherwise, you will want to plant tomatoes in the spring, as a crop that matures in summer to early fall. For more information (and to find your plant hardiness zone), you can check out the USDA Zone Hardiness Map here. If you aren’t in Zone 10, you should have your tomatoes transplanted outside by late May or early June in order to harvest before the first frost. Example 1: Brandywine Red Tomato Planting Date Let’s go through the calculations for a variety that takes a bit longer to mature. For example, a Brandywine Red tomato plant will take about 85 days to maturity (note: this is the time from transplant to maturity; it takes 8 weeks or 56 days extra to grow from seed to transplant!) So, if you plant on the last day of May (May 31), then it will take 30 days in June, 31 days in July, and 24 days in August (85 days total) to mature by August 24th. Of course, it will continue producing after this point in time, possibly well into September. Of course, you should add in a "harvest buffer" to give the plant time to produce fruit. It would be a shame to only get a little mature fruit on the first fall frost date and lose the plant after a short harvest! Example 2: Fourth Of July Tomato Planting Date As another example, if you planted a Fourth of July tomato plant on May 31, then it will take 30 days in June and 19 days in July to mature by July 19. Of course, if you really want tomatoes on July 4, you will need to plant two weeks earlier, on May 16 or earlier. A Few More Words On Tomato Plant Start Dates Remember that time to maturity varies depending on climate conditions. It will also be longer if you are starting seeds instead of seedlings or established plants. If you want to get an earlier start and avoid late spring frosts, you should start your seeds indoors in March or April, and transplant them outdoors in late April or early May. Start tomato seedlings indoors in late winter or early spring, about 8 weeks before your transplant them outdoors. You can also use the Old Farmer’s Almanac to check last spring frost dates by zip code. Remember that tomatoes will not grow below 50 degrees Fahrenheit, so it is pointless to plant them outside before temperatures warm up. In fact, you may even kill the plants with a late spring frost! When you do put your tomato plants outside, make sure to protect them from the cold and let them get accustomed to the temperatures. How To Protect Tomato Plants From Cold There are a few ways you can protect your tomato plants from cold. We already mentioned starting them early indoors. You can also grow them in a greenhouse, or use row covers when temperatures get cold. Growing Tomatoes In A Greenhouse If your greenhouse is warm enough, you can start seeds in March or April. Then, you can transplant them to the soil outdoors in May. The temperature inside a greenhouse can be warmer than the outside air temperature by 10 degrees or more. Of course, the difference will depend on how well-sealed and insulated it is. A greenhouse can let you start tomato plants outside earlier, and protect them from early fall frost. Just be sure to open the door or allow ventilation on a hot day with lots of sun. Otherwise, your plants will get too hot. Also, remember to transplant them outside once they start flowering, to allow for pollination by bees. (Yes, tomato plants are self pollinating, but this does not mean guaranteed pollination - bees can really help them along!) Using Row Covers To Protect Tomatoes From Cold You can use row covers to protect against late spring or early fall frosts. A row cover is made of fabric that protects plants from cold (and insects), but also allows sunlight through. Row covers keeps tomato plants warmer in the cold, possibly keeping them alive on a frosty night. Agribon is one brand of row cover with varying grades of protection. For example, Agribon AG-70 can protect plants down to 24 degrees Fahrenheit. For more detailed information on cold protection, check out my article on protecting tomato plants from frost. What Happens If Tomatoes Are Planted Too Late? If you plant your tomatoes too late, you may encounter problems due to heat in the summer or problems with cold in the fall. Problems With Heat In The Summer The first and most obvious problem you will encounter when planting too late in the summer is the heat. Tomato plants may delay flowering if temperatures are too high. Higher temperatures and brighter sunlight also lead to soil that dries out faster. Remember that that young tomato plants are not yet established with strong roots. As a result, they cannot withstand prolonged drought. This means that you will need to work hard to stay on top of keeping them watered. (This can be a big chore in a large garden during a dry summer!) Another less obvious problem with planting too late is summer humidity. When humidity is too high, tomato plants can fail to pollinate properly (the pollen sticks to the male part of the flower and is not released onto the female part). Tomato flowers may have trouble with pollination if it is too humid. Even if you manage to navigate watering and pollination, you may also encounter problems with pests. Younger tomato plants will not be as resistant to pests as more established plants. In fact, a few pests could damage your plant and quickly spread to others in your garden. For example, aphids can multiply fast - learn how to get rid of them in my article here. Problems With Cold In The Fall Even if you manage to contend with summer heat and humidity, you still need to worry about frost hurting your tomato plants in the fall. Tomatoes will not grow in temperatures below 50 degrees Fahrenheit, and a frost will damage or kill them. Even prolonged exposure to temperatures in the low 50's Fahrenheit can be a problem. Harvest your tomatoes before frost, or else they fruit will get damaged and the plants will succumb to the cold. As mentioned earlier, consider using row covers to protect them from an early fall frost and to keep them growing when it gets cooler. You can learn more about the coldest temperatures tomato plants can tolerate in my article here. Conclusion Now you have a better idea of when to plant your tomatoes - and when it might be too late to do so. If you waited too long to plant outdoors, you still might be able to grow some tomatoes indoors in a pot or container on a windowsill. I hope this article was helpful - if so, please share it with someone who can use the information.