Temperature & Humidity

beans in top drip pot

It's not enough to just designate a spacious, well lit area for your new hydroponics garden. You need to provide the appropriate microclimate for maximum production.

Proper temperature and humidity also repels bugs, algae, fungus and disease.

How to Grow Hydroponics:
Temperature Requirements


Okay, so maybe you're tired of hearing this by now... but it's so important! The proper temperature range is such a basic and crucial element to a successful hydroponic garden that we don't want you to overlook it! Remember the magic optimal range: 65-80°.

There are two types of vegetable crops, each requiring a different temperature range:

  • Warm season crops and herbs: [tomatoes, peppers, eggplants, cukes, beans, squash, melons, herbs]

    70-80 degrees; Nighttime: 60-70 degrees. Absolute max temp=90 degrees
  • Cool season crops: [broccoli, cabbage, lettuces, endive, peas, spinach, green onions]

    60-70 degrees; Nighttime: 50-60 degrees. Absolute minimum temp=40 degrees

Yes, you can mix them up some (like growing lettuce with tomatoes) by compromising on temperature. But in general, you'll have the best results if you grow seasonal crops together, grouped as above. So you can stay within the best temperature range.

More on seasonal crops and when to grow them here: Hydroponic Vegetables.

How to grow hydroponics:

You might get the idea that since warm temperatures seem to spur plant growth, then why not keep it warm in there 24/7?

Well, it just doesn't work that way. Plant metabolism requires a cool-down at night. For optimal plant growth and crop production, shoot for a 10 degree drop in temperature at night (at the same time the grow lights are off).

They make a thermometer which records the high and low temperatures reached during the day. This is very helpful:

minimum/maximum thermometer

Or get a combination thermometer/hygrometer (+humidity readings) and place the probe near your plants.

This one, from EcoPlus, has large, easy-to-read numbers:


You can order either one of these Instruments here: Cheap Hydroponic Supplies.

At the bare minimum, you absolutely need a plain thermometer, under the grow lights, where the plants are.

How to Grow Hydroponics: Humidity

orchid greenhouse

Have you ever been in a moist and humid orchid greenhouse? Then you might have the idea that the highest possible humidity would be best for your hydroponics crops, too. But this is not so. The optimal humidity range for vegetable crops is 50-80% RH (relative humidity), with 50% being the best.

If it gets too humid, plants are unable to transpire (breathe) properly. Very humid air is also perfect for powdery mildew and nasty funguses to take hold.

Very high or low humidity makes pollination difficult (a very important process addressed fully here: Plant Pollination).

Get a hygrometer or thermometer-hygrometer combo and hang it right in your unit so you can keep tabs on this daily. You may be surprised to see how low the humidity in your air-conditioned or gas-heated living room really is.

How to raise the humidity in your garden space? Buy an inexpensive room humidifier or vaporizer and plug it in next to your unit. These are cheap, too. This one costs $26 at WalMart:


Chances are slim that your inside humidity is too high, however, the cure for that is a fan, which you need, anyway. Air movement helps prevents mold and fungus, and promotes air exchange.

Now, listen... you don't want your crops blasted with a big box fan set on high. What you do want is a small oscillating (turning) fan set on low to gently refresh the humid, stale air around your plant's leaves. You want to see slight, gentle leaf movement. This fan should be left on 24 hours a day.

These are cheap, too. They cost about $15:

cheap fan
oscillating fan

Yep, you guessed it... WalMart. Oh, throw in another $5 and get the floor model.

exhaust fan

If you have set up in a damp basement, you might want to invest in a portable dehumidifier unit (good anyway, to help prevent mildew).

And if you are growing in a closed-off room, with no windows, you may need an exhaust fan to vent the moisture and stale air to the outside, like the kind used in a bathroom.

Return From How To Grow Hydroponics to Climate


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