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Temperature and temperature ranges come up in our discussions here at Plant to Plate. Each gardening facts article has an ideal temperature range section for the plant being discussed. For example, our Growing Carrots article makes this statement:
Carrots grow fastest in temperatures of 55-75°F.
This is their ideal temperature range. Although they will grow in temperatures both cooler and warmer than this range, the growth could be slower or even stunted.
Minimum and maximum temperatures will vary by variety. Some carrot varieties are bred for fall harvests and others for warmer climates.
What is an ideal temperature range? Why does temperature matter? How does it affect plant health? Read on to find out.
Jump to: What it is | Why it matters | Where to find it
What is an Ideal Temperature Range?
An ideal temperature range lists the temperatures that allow for a plant's best, fastest, healthiest, and most productive growth.
This range includes the approximate upper and lower temperature limits for this type of growth. It is written in a format such as 55-75°F.
Keep reading to learn why the temperature range matters to gardeners and how it affects plant health.
Why Temperature Matters
Let's start with the basics. Each plant's range of temperature tolerance and hardiness is different. If the temperature is outside a particular plant's tolerance range, the plant will die. This can happen immediately or after it bolts. Temperatures that are not outside the tolerance range may not kill the plant, but it may experience stress and stunted growth. See the If a Plant Gets Too Cold and If a Plant Gets Too Hot sections below.
But again, ideal temperature does not describe the plant's minimum and maximum temperature tolerances for survival. It describes the temperatures that promote its best, fastest, healthiest, and most productive growth.
As mentioned in the carrot example above, a plant may grow in temperatures above and below its ideal temperature range. Carrots' ideal temperature range is 55-75°F, but many carrot varieties are hardy to around 35ºF. Most carrots will bolt when temperatures reach the upper 70s. But there are a few varieties that are bred for hotter climates and may tolerate higher temperatures, especially if grown in the shade.
So what happens in the temperatures between the tolerance range and the the ideal temperature range? For example, what if a carrot finds itself in 40ºF temperatures for a few weeks?
Basically, in this range, growth will probably still occur, but it may be slower. Fruits, roots, and leaves produced during that time tend to experience problems similar to when sun-loving plants are grown in the shade due to the longer, slower growing time. See our What Does "Full Sun to Part Shade" Mean? article here for an explanation of these problems.
So it is best to keep plants within the ideal temperature range for as long as possible. Keep this in mind as you plan the layout and timing of your garden.
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But heatwaves, cold snaps, and other temperature swings happen! What should you do if your plant gets too cold or too hot?
Read on to find out!
If a Plant Gets Too Cold
If the temperature is too cold for a particular plant, the plant may die. For some tropical plants, this can happen at relatively cool temperatures like 50-55ºF. For many plants, it may be around freezing (32ºF), especially if the plant experiences frost. Other cold-tolerant plants may survive much lower temperatures such as Red Ursa kale, which is hardy to around -10ºF.
A plant may die immediately when it experiences temperatures below its tolerance. In other cases, it may survive but show significant signs of stress. Sometimes it can be saved by bringing it to warmer temperatures and giving it extra water. Afterward it may return to its normal state, or it may experience slower or stunted growth for the rest of its life, depending on the extent of the damage.
If you know temperatures below your plant's hardiness range are coming, you can bring the plant inside or cover it with a cloche or similar cover. I like this one.
If a Plant Gets Too Hot
If the temperature is too hot for a plant, this could have a few different outcomes. Many cool-weather plants will bolt and go to seed. This is especially true of leafy greens like arugula and chard, herbs like lemon balm and chamomile, and plants in the Apiaceae family like carrots, cilantro, and dill. Other plants may die immediately.
Additionally, a plant that gets too hot may experience stunted growth, either temporarily or permanently. Tomatoes and peppers are notorious for this. They are (moderate) heat-loving, warm-weather plants that are grown as summer annuals in many places. However, if temperatures exceed the upper 80s for tomatoes or the mid-90s for peppers, the plants will stop producing fruit. This is usually a temporary pause, and fruiting usually resumes when temperatures cool. But in some cases, it can negatively affect the plant's production and health for the rest of the season. Tomato plants may die if temperatures remain above 95ºF for an extended time, especially if protective measures are not taken.
Heat stress can be avoided or reduced by using methods that lower the temperature around the plant. The easiest way to do this is by adding shade. This can be done by moving the plant into the shade or using a shade cloth to cover the plant. I like this shade cloth.
Where to Find Temperature Information
Each of our gardening facts articles contains an ideal temperature range section. You can access it by going to an individual plant's gardening facts page. From here, you can click on "Temperature Range" from the "jump to" menu at the top of the page, or you can scroll down to the section itself, which starts with "What is the ideal temperature range for..." such as this one for lavender.
Our gardening facts articles are mainly intended as quick references for busy gardeners. So we usually keep them concise and brief, listing the temperature range with a quick note summarizing how the plant is affected by temperatures outside of its ideal range.
But if a plant has additional considerations, we will include those as well. For example, our Growing Kale article makes this note:
Kale is one of the hardiest vegetables. Hardiness varies greatly by variety, but Red Ursa and other hardy kales can survive at temperatures down to -10°F.
Most kales pause their growth in the winter, but the fact that they can survive winter makes them an excellent biennial choice for colder regions. You may choose to overplant kale that matures in the fall so that you can continue to harvest its leaves throughout the winter.
And our Growing Amaranth article includes this information:
In general, amaranth tolerates and even prefers heat much more than its cousins, spinach and chard. Although its growth may be slower in temperatures above 85°F, many varieties can tolerate temperatures up to 110°F, especially if they receive some shade, as noted in the sun conditions section above.
But as a warm-weather plant, amaranth does not tolerate cold as well as its cousins. Some varieties are hardy to about 50-55°F, while others may survive down to around 40°F.
So supplementary temperature information is included in this section for plants with more specific needs or other applicable considerations.
Some seed packets and some seed companies' websites also list an ideal temperature range for the specific varieties they sell. This varies by company.
Read More
Check out these articles about other growing conditions that affect plant health:
- How Often to Water Plants
- How Much Sun Does My Plant Need?
- What Does "Full Sun to Part Shade" Mean?
- Choosing the Right Planter for Your Container Garden
- Companion Planting Basics
- What is a Heat Zone?