The Best Soil Temperature for Seed Germination
The anticipation and excitement that come from sowing seeds for a favorite flower or vegetable can lead to disappointment weeks later when many, if not all, of those seeds have failed to germinate. While many factors affect germination — from the age and quality of the seed to the depth of planting — the most challenging for gardeners and often least understood is soil temperature. Learning the best soil temperature for seed germination will go a long way towards your seed-starting success.
Warmer temperatures speed up chemical reactions and, conversely, cooler temperatures slow them down. Those chemical reactions help break down the protective seed coat and tell the seed that it’s time to wake up and start growing. For a cool-season leafy crop like spinach, the ideal temperature for germination can be as low as 50 degrees Fahrenheit. For heat-loving tomatillos, the minimum desired soil temperature is 80 degrees.
Starting plants from seed is a fun and rewarding gardening activity. Many factors affect seed germination, but the most challenging for gardeners and often least understood is soil temperature.
While there is can be variation from one seed type to the next, most seeds for warm-season edibles prefer soil temperature between 70 and 80 degrees Fahrenheit (21.1 and 26.7 Celsius). When the soil temperature in your garden is too cool — or too hot — seeds may take longer than expected to germinate or will never germinate at all. Whether direct sowing seeds in the garden or starting seeds indoors, achieving the optimal soil temperature before planting will greatly increase the germination rate and also result in more vigorous plants.
Want to know what the ideal soil temperature range for optimal germination for the most commonly grown edibles? Download our free pdf that puts that information right at your fingertips for ready reference.
Indoors, seeds often require warmer temperatures than the average house is heated to in spring. Outdoors, even after your last frost date of spring, the soil will continue to remain cooler than the air temperature until it has had weeks to heat up. But before using the tricks to raise soil temperature, its important to know where you are starting from.
Checking Soil Temperature
All it takes to find out the temperature beneath the surface of your garden is an inexpensive soil thermometer. A soil thermometer typically has a 6-inch probe, but 6 inches is deeper than necessary for seed starting. Stick the thermometer between 1 and 2 inches into the soil and wait close to 30 seconds to get the most relevant and accurate temperature reading.
Take a reading in both the daytime and the evening, and calculate the average. If you have multiple plantings areas — especially if some get more hours of direct sunlight than others — don’t assume that they will all be the same temperature. Record the temperature of each.
You can use an inexpensive analog or digital soil thermometer to find out the soil temperature in your garden or seedling trays.
Raising Soil Temperature Outdoors
A south-facing garden will heat up faster than others, and a raised bed garden or container garden is typically warmer than ground level. Wherever your garden is sited, if you find that your soil temperature isn’t where it needs to be, you can heat it up with plastic sheet mulch. Clear or black plastic mulch will take advantage of solar energy to raise the temperature of soil by several degrees and will hold that heat overnight.
To increase both the soil and air temperature, use a cloche or a cold frame. Both trap heat like mini-greenhouses and are excellent for extending the garden season. They may be made out of glass or plastic. The lids of easy-to-build homemade cold frames are often made from up-cycled window sashes.
Soil covered in mulch (wood chips, bark, shredded leaves, straw, etc.) will take longer to heat up in the spring, so rake away and remove the mulch after the last hard frost. (You can always reapply mulch after your seeds have sprouted or your transplants are in the ground.)
Cold frames trap heat like mini-greenhouses and are excellent for warming up soil and extending the garden season.
Raising Soil Temperature Indoors
Indoors, you may be starting your seeds in a soilless potting mix, but the same principles apply: For the most successful germination, get the growing medium into the ideal range for the seed.
A bag of soilless mix that got cold sitting outdoors or in an unheated garage isn’t an issue, because that is quickly resolved by adding warm water into the mix when preparing your cells or soil blocks. Still, room temperature will not be warm enough for many seeds to perform their best and achieve a high germination rate.
Also known as germination mats, seed-starting heat mats placed under seed trays will raise the temperature of the soil by approximately 10 degrees. So in a house kept at 65 degrees, the seed trays will get up to about 75 degrees — the ideal temperature in most cases.
The mats are thin, waterproof and come in many sizes. The most sophisticated seedling heat mats include thermostats to reach a precise temperature. These are helpful in a cool basement where an extra 10 degrees won’t be enough.
A heat mat with a digital thermostat is perfect for maintaining soil temperature at a specified number.
Online Gardening Academy™ Seed Temperature Chart
To learn the soil temperature range for optimal germination for common vegetable seeds, click to download the Online Gardening Academy™ Seed Temperature Chart.
Links & Resources
joegardener Online Gardening Academy™ Three popular online courses on gardening fundamentals; managing pests, diseases & weeds; and seed starting!
Cannabis temperature: know the ideal temperature for growth
So, you want to grow cannabis but aren’t too sure what the right temperature is for your weed plants to flourish.
Figuring out the ideal cannabis temperature for your particular strain is essential to a fruitful harvest.
In this article, you’ll discover all you need to know about controlling the temperature and what to do if it gets too hot or cold.
Why is the temperature important to grow cannabis?
Unfortunately, unlike animals, plants cannot create their own heat. A cannabis plant’s ability to grow and to its fullest potential heavily depends on the skill and expertise of the grower.
Temperature affects rates of cellular respiration, photosynthesis, and the prevalence of disease in cannabis—making it an essential aspect for the cultivator to control.
The effects of temperature on cannabis growth
The temperature for growing weed plays a significant role in cannabis growth. Let’s take a closer look.
Temperature and photosynthesis
Photosynthesis is positively affected by temperature until a certain point. Hotter than that, and the high temperatures begin to harm the plant. Lower temperatures, on the other hand, cause slower growth and a low yield.
Temperature and respiration
A higher marijuana growing temperature significantly increases cellular respiration, where it becomes more than the rate of photosynthesis. When temperatures lower, respiration decreases, and so does the rate of growth.
Temperature and disease
Like humans, cannabis plants are susceptible to disease—some diseases persevere better in warmer temps, while others in colder temperatures.
Growers more commonly encounter gray mold in cold climates with moisture. Root rot is more likely in summer, and pathogens like powdery mildew grow in humid conditions.
Best temperature ranges to grow weed
Manipulating the environment to the ideal temperature for growing weed is vital. Below you’ll find our best suggestions for the choice of temperature at the different stages of growth.
|Clones and Seedlings||The perfect cannabis seedling temperature is between 68–77°F/20–25°C.|
|Vegetative stage||This stage is best done between 68–77°F/20–25°C.|
|Flowering stage||The best temperature for flowering cannabis is between 68–77°F/20–25C°.|
|Late flowering||Here you can lower the temperature a little bit to about 64–75°F/18–24C°.|
|Drying and curing||The best temperature and humidity for drying cannabis should be at about 70°F/21C°, and humidity at 50%.
Curing should happen at around the same temperature but between 58 and 65% humidity.
|Indica||Indica strains do better in colder climates than other strains. Popular strains include Purple Kush, Northern Lights, and Blue Cheese.|
|Sativa||Sativa strains normally do better in warmer environments. Good strains include Durban Poison, Lemon Haze, and Strawberry Cough.|
|Hybrid||This depends on whether it’s indica or sativa-dominant. Indica-dominant strains do better in cold climates, while the reverse is true for sativa strains.
Marijuana users enjoy hybrid strains such as Blue Dream, OG Kush, and Pineapple Express.
What happens when the temperature is too hot?
Figuring out the right growing weed temperature isn’t easy. The heat will restrict plant growth if it’s too warm, and the cannabis leaves will begin to curl.
How do you fix the temperature?
There are several easy options to get the best temperature for weed.
You can opt to move your grow lights away from your plants. Alternatively, you could increase circulation by using a fan.
For outdoor plants, you should water them both in the morning and the evening. You may also want to introduce artificial shade should the heat become an issue.
Indoor marijuana grow tents are a great way to deal with temperature issues if you’re currently planting indoors.
What happens when the temperature is too cold?
If the marijuana growing temperature is too low, this can stunt growth or even kill your cannabis plant. Getting a marijuana growing calendar is an excellent idea as it shows you the average temperature per month and other helpful information.
How do you fix the temperature?
There are certain aspects out of your control.
If you live in a colder climate, buying marijuana strains that grow well in cold environments may be better. Indica strains should be your go-to for this.
Additionally, some plants do better indoors, so growing inside might be preferable to moderate temperature. Grow lights, heating mats, and space heaters are the privileges of the indoor cannabis grower.
How can you control your growing room temperature?
Maintaining the ideal marijuana growing temp is paramount to having an excellent harvest.
Here are a few things that you can do to control the cannabis temperature:
- Account for the wattage of your lightning. Higher wattage bulbs put off more heat and pose a risk to your cannabis. Stay on top of temperature monitoring in this case.
- Adjust your light schedule. Many growers keep their lights on all day. If you need to reduce the temperature, switch them off for a few hours a day.
- Add CO2 to the air. It’ll make it so that your plants can survive higher temperatures and induce faster growth.
- Install some oscillating fans, which help with temperature and aid in preventing mold.
- Make sure that your growing room is sealed and insulated.
- If all else fails, try supplements. These can help make your plants become more resistant to warmth and recover better from heat.
Unique concerns for outdoor growers
Indoor growing helps you evade the common issues found when growing cannabis outdoors. It’s much easier to get the best temperature to grow marijuana in a controlled setting.
That said, you can try these solutions and suggestions if you prefer the idea of growing outdoors.
Greenhouses and cold frames
Getting a greenhouse will help you control the ideal temp and humidity for cannabis. The best choices for cannabis growth include polytunnel, lean-to, and freestanding greenhouses.
If you’re looking for something a bit smaller, you can always opt for a cold frame. It protects your cannabis from cold weather while still getting heat from the sun. They’re cheaper than a greenhouse and suitable for small-scale outdoor growing.
Patio heaters are perfect for cold regions and will help keep your plants warm. You can also opt to use it only at night.
Compost generates heat while it decomposes and so will naturally make the surroundings warmer. Placing compost piles near where your cannabis grows will aid by raising the temperature.
Choose the right seeds
The optimum cannabis germination temperature is 78°F/25°C. That said, there are slight variations according to strain. The rule is that indica is better for cold temperatures, while sativa is better in warmer climates.
Drying and curing
Drying and curing aids in making your buds not only smell better but become more potent as well. You need to ensure while drying cannabis buds you retain the temperature at about 68°F/20°C, and three days later, at about 61-64°F/16-18°C.
Curing is best done slowly at low temperatures. Some connoisseurs even leave their buds to cure for up to a year!
FAQs related to cannabis temperature
If you’re looking for simple answers to complex questions, read through our frequently asked questions.
What temperature does cannabis grow best at?
Temperatures can vary, but for the most part, the best marijuana-growing temperatures are between 20–30°C/70–85°F during the daytime. At night the best temperature to grow weed is 25°C/75°F.
Can a negative temperature differential make the cannabis plant sick?
You can use a negative temperature differential to keep your plants stocky and short. However, it can harm certain strains, so you need to do research beforehand to determine whether it’s safe or not.
Can fluctuations in temperature stress cannabis?
Yes, it’s important to moderate the temperature as much as possible. A stressed plant will begin to get yellow leaves, and brown spots can begin to appear.
Can indoor temperature swings damage cannabis?
Yes, it’s crucial to maintain consistent cannabis-growing temperatures. If the temperature is too high, it can degrade terpenes and stress the plant, resulting in damage. If the temperature is too low, it can damage nutrient uptake and negatively affect growth.
What is the best temperature for drying cannabis?
The best grow room temp, and humidity for drying cannabis is more or less 70°F/21C° with a humidity of 50%.
What temperature will the buds on a marijuana plant stop growing?
At below 15°C/59°F, marijuana plants will struggle to grow and may end up dying. Cold temperatures slow the rate of photosynthesis. It helps to refer to a cannabis temperature chart if you’re unsure about a specific strain.
What humidity should the marijuana grow room be?
The humidity for growing weed should be upwards of 70% at the initial stages, but you should reduce it to 40–50% as it reaches the flowering stage. It can go up to 60% during the vegetative stage.
What is the lowest temperature cannabis can survive?
The lowest weed growing temperature depends on the strain. However, as a rule of thumb, anything below 50°F/10°C will cause a lot of strain on the plant.
An important variable
As you can see, determining the optimum weed temperature plays an essential role in the growth and survival of cannabis plants. The fruitfulness and survival of your plants is all determined by the effective implementation of temperature control.
At i49, we have the right seeds for you and your unique temperature concern. Check out our website to see what we offer.
- Cannabis Consumption
- Edibles & Recipes
- Oils & Concentrates
- Ways to Smoke Marijuana
- Cannabis News
- Legalities of Growing
- Germination & Seedling Stage
- Time to Harvest
- Vegetative & Flowering Stage
- Climate Control
- Indoors 101
- Lighting Requirements
- Your Grow Room
- Climate and Weather
- Outdoor Grow Calendars
- Outdoors 101
- Beginners Guides
- Plant & Seed Types
- Setting Up: Tools & Equipment
- The Cannabis Plant
- Hydroponic Growing
- Optimizing Yields
- Pruning Techniques
- Sexing & Making Seeds
- Animal and Insect Pests
- Fungi & Other Diseases
- Growing Issues
- Nutrient Problems
- Medical Conditions
- The Latest Cannabis Research
How to Identify a Female Marijuana Seed 15 March, 2020 How to Identify a Quality Marijuana Seed Ask any e. Read Article
Hydrogen Peroxide and Cannabis 1 May, 2020 The Benefits of Hydrogen Peroxide in Hydroponics a. Read Article
How to Speed Up Flowering of Outdoor Cannabis Plants 2 April, 2020 A good deal of cannabis horticulturists grow their. Read Article