Bacteria can grow in cool conditions. They will even grow, albeit very slowly, inside your fridge. Most species, though, grow considerably faster at about 95 degrees Fahrenheit. Unless you wish to wait weeks for your cultures to develop, you’ll need some sort of incubator. This could simply be a warm spot, for example near a heater, but a purpose-built incubator makes things easier and allows you to control the temperature variable.

Find or make a wooden box large enough to hold all your petri dishes when it is on its side. The box can be as crude as you like -- its only purpose is safe insulation.

Drill a hole in the side of the box, if one doesn’t already exist. This is for the cord to the lamp.

Place a small desk lamp in the box. Use a 15 watt bulb -- you don’t need anything more for an incubator this size and a stronger bulb could overheat it.

Create a platform with wood or cardboard over the lamp. For example, fold a piece of cardboard so that it has two sides a little higher than the lamp and a wide middle and pop this over the top.

Measure the temperature above the platform after a few hours. If it is about 80 to 95 degrees Fahrenheit, you have the perfect incubator. If it is considerably higher or lower, use a different bulb, wait and test the temperature again.

Place your cultures on the platform in the incubator.

Items you will need

  • Wooden box

  • Drill

  • Desk lamp

  • Cardboard

  • Thermometer


  • You can stack petri dishes if space is short.

    An old aquarium --minus the water of course -- would make an excellent incubator, especially if you have a reptile heat mat to provide warmth.

    You can repurpose scrap pieces of furniture as incubators. A small bedside cabinet, for example, would be ideal.


  • Don’t be tempted to increase the temperature drastically in the hope that your bacterial colonies will grow faster. Not only are high temperatures likely to kill some or all of the bacteria, but you’re also creating a fire hazard.