Temperature and Humidity – Page 2

Maybe this is your first year planting tomatoes, or you just got busy and forgot to plant your garden. 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 a first crop of tomatoes, you should plant by the end of May. In warmer climates, you may be able to plant a second crop later in the season. Also, how late you can plant depends on the days to maturity, which depends on the variety of tomato you choose. You can extend your growing season by starting seeds indoors at the start of the season, 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. 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: the first frost date and the time to maturity. 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. You want to make sure your plants are mature and harvested before the first frost of the fall season! A frost will kill most unprotected plants and damage fruit, including tomatoes. So, you will want to make sure that your plants mature and harvested before the first frost date. The first frost date will depend on your location. 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! 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 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. 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: Fourth of July (hybrid) – this 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. Umamin (hybrid) – this 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. Summer Girl (hybrid) – this 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. Mighty Sweet (hybrid) – this 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. Bloody Butcher – this variety of 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. 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 late summer to early fall. For more information and to find your zone, you can check out the USDA Zone Hardiness Map here. If you aren’t in Zone 10, you should have your tomato seeds planted by the end of May in order to harvest before the first frost. Let’s go through the calculations for a variety that takes a bit longer to mature. A Brandywine Red tomato plant will take about 85 days to maturity. 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. 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. 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. 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, and transplant them to the soil in May. The temperature inside a greenhouse can be warmer than the outside air temperature by 10 degrees or more, depending 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, or else your plants may get too hot. Also, remember to transplant them outside once they start flowering, to allow for pollination by bees. 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. 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 more quickly. Remember that that young tomato plants are not established with strong roots. 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. 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. A few pests could damage your plant and quickly spread to others in your garden. Problems With Cold in the Fall Even if you manage to contend with summer heat and humidity, you still need to worry about frost in the fall. Tomatoes will not grow in temperatures below 50 degrees Fahrenheit, and a frost will damage or kill them. As mentioned earlier, consider using row covers to protect them from an early fall frost and to keep them growing when it gets cooler. Conclusion Hopefully, this article gave you some idea of when to plant your tomatoes. If you waited too long to plant outdoors, you may 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. If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here. Enjoy! ~Jonathon