Ideal grow room temperatures are more than just what shows up on a single thermometer in your grow room. While it’s easy to give you the ideal indoor grow temperature (between 65°F and the low to mid 80°F’s) we know that it’s not simply the room temperature alone that helps you get the yield you want. We're going to go over the affect temperatures play in your grow room, from the temperature outside your growing space to the grow lights inside of it.
The Effect of External Conditions on Internal Temperatures
One of our biggest questions from growers is, "What effect do outdoor temperatures have on my indoor grow room?" To answer that, it helps to know whether you want to grow in a grow tent or you want to convert a room in your house to grow your plants in.
When Growing in Your Room- Outdoor conditions can play a huge role in your room. Summer heat can raise the temperature of your grow exponentially (especially when you’re using HID grow lights). Without lots of insulation, the heat outside will raise temperatures in your growing area and make it hard to maintain a good environment. Winters can make temperatures hard to maintain during your plant's sleep cycle. Outdoor night temps can drop your grow’s temperature from the 70’s down to the ’40s within hours, which can create excess moisture around your lights and plants. On top of stunted growth, the excess moisture and humidity created can also cause mold. When Growing in a Tent- Reflective grow tents have a little more of a buffer, provided the temps around your tent are okay. If you can maintain a good temperature in your home or apartment, you’ll be able to control a tent’s temperatures easier, too. Even if temperatures in the surrounding area are hard to manage, grow tents have an area that can be cooled and warmed much easier than an open room. No matter what the application, outdoor temperature can (and usually will) affect your grow. However, it’s up to you how/if you regulate how much of an effect it’ll have on your grow.
Ambient temperature is the temperature your growing space sits at. It's affected by external factors like the temperature outside, as well as internal factors like the heat (or lack of) coming from your grow light.
Temperatures inside of your garden play a big role in how well your plants breathe and absorb nutrients. The ambient temperature of your grow room plays a huge factor into the humidity level in it, which will affect how much your plants will sweat, absorb nutrients, and ultimately grow. Excessive heat will make your plants breathe and lose water quickly, while excessively low temperatures will slow down the absorption of nutrients, stunt growth, and can lead to moisture build-up (and all the problems that come with it). Photosynthesis in plants can only be achieved at certain temperatures, so even if the humidity of your growing space allows your plants to breathe properly, a bad temperature may not allow for your plants to convert nutrients into usable energy for your plant to grow. Your plants are constantly trying to grow, and when temperatures are off it makes it difficult for the plant to do so. No matter if your plants like it tropical or cool and dry, knowing the ambient temperature of your growing space is important in making sure your plants are getting what they need to convert nutrients into usable food. That includes making sure the temp in your room isn't affecting the temperature of your water or medium temperatures. Common grow room temperatures include (but are not limited to):
- Clones/Seedlings: 72-82°F
- Vegging Stage: 68-78°F
- Flowering Stage: 68-77°F
- Temperature Drop: 10-15°F
If you’re not careful when it comes to grow room temperature regulation, you can unknowingly overheat the canopy of your plants. If the canopy temperature's off then your plants can't perform photosynthesis.
Canopy temperature is the temperature at the canopy (leaf) level of your plants- simple enough, right? So then it makes sense that canopy temperatures should be around the same as the ambient temperature of your room. When you set a thermometer at the canopy level of your grow you should see a reading within the normal range your room sits at. Plants are pretty resilient, so a few degrees outside of that range won’t hurt. If it’s far outside of the ambient temperature you’ll need to adjust something in your grow room. When you should raise your lights- When your grow lights are too close, your plants have a chance of overheating your canopy. If you're using HID grow lights and temps are too high at the canopy level (say, close to 100°F) raise your lights. When to bring lights closer- When lights are too far away your canopy might get too cold and that will contribute to stunted growth, so bring the lights closer to the canopy. Of course, variables can skew these solutions- LED grow lights, for example, don’t generate much heat, so ambient and canopy temps can be relatively lower than most. In those cases that you're not using HID's, you’ll want to add a heater or A/C unit into your grow to mediate temperatures.
Ambient temperatures will affect the temperature of the nutrient-rich water you're feeding your plants and the soil they grow in- i.e. your plants' grow medium. The temperature of your grow medium is important to know because if it's not on point your plants are going to have trouble eating. Your medium's temperature should be around where your room is at, if not a little cooler. For example, if your room is at 77°F your nutrient-rich water or soil should be within the 72-77°F range. When a grow medium is too cold nutrients won't be able to break down much before they're taken up by the plant. Whether you're going in soil or you're soilless, if your plant's roots are too cold they won't be able to absorb nutrients effectively. Feedings won't be processed, you'll stunt your plant's growth, and with enough unprocessed food and bad temps, you can start to see waterlogging and root rot. When a grow medium is too warm it can lead to root rot and mold at the root zone in hydro gardens (usually due to swampy conditions near the root zone). While the soil is resilient, you should make sure your soil temperatures are also within your ambient temperature range. If it gets too hot at the soil level you can be frying your roots. Fried roots can't take in nutrients, which will start to kill your plant.
Temperatures all connect to get you the yield you want, and if there are conflicting temps in your grow room your plants can suffer. If canopy's too high, then it's likely soil's too high so your plants can burn. If the water's too hot but your canopy is right, you could be messing up your roots or exhausting your plant- the bad combos are endless. There's always a little wiggle room when it comes to correct temps, so the key is listening to your plants and making sure you give them they temperatures they like, not the temps they can withstand. Remember: just because a plant can withstand high or low temps doesn't mean you should subject them to unhealthy conditions.