Beginner’s Guide: How to Heat a Greenhouse in Winter

Keeping a greenhouse warm in winter can feel difficult when you are just starting out, but it does not have to be complicated or expensive. The goal is to hold on to as much heat as possible, add gentle warmth when needed, and protect plants during the coldest nights. This guide explains simple, beginner-friendly ways to keep your greenhouse warmer through winter.

1. Start with Passive Heat

Passive heat means using natural warmth from the sun and storing it inside the greenhouse. This is usually the best place for beginners to start because it costs little and works well when combined with insulation.

Good passive heat materials include bricks, stones, soil, compost, and water containers. These materials warm up during the day and slowly release heat after the sun goes down.

Beginner tip: Place heat-storing materials where they will get the most sunlight, such as along a south-facing wall or on a sunny greenhouse floor.

2. Insulate the Greenhouse

Before adding heat, make sure the greenhouse can hold on to the warmth it already has. Insulation helps reduce heat loss and makes every heating method more effective.

Bubble wrap is a simple and affordable insulation option. Use greenhouse-grade bubble wrap if possible because it lets light through while adding a layer of protection against cold air.

Cut the bubble wrap to fit the inside panels, lightly mist the glass or plastic with water, and press the bubble wrap into place. You can also wrap individual pots or seed trays for extra protection.

Beginner tip: Check for gaps around doors, vents, and panels. Even small drafts can quickly lower the temperature inside a greenhouse.

3. Use Compost for Gentle Heat

Compost creates heat as organic material breaks down. A compost bin or hotbed inside or near the greenhouse can add gentle warmth while also producing useful compost for your garden.

Materials such as straw, leaves, wood chips, and manure can all help create heat as they decompose. The compost should stay moist, but not soaked, so the process continues steadily.

Beginner tip: Compost heat is helpful, but it is not always enough on its own during freezing weather. Use it together with insulation and other heat-storing methods.

4. Add Water Barrels or Black Water Containers

Water holds heat well. Large water containers can absorb warmth during the day and slowly release it at night. Black containers work especially well because they absorb more sunlight.

Place water barrels, jugs, or black water butts in sunny areas of the greenhouse. If possible, set them on a solid floor, such as concrete, so the surrounding surface can also help store heat.

Beginner tip: Keep containers filled. A full container stores more heat than an empty or partially filled one.

5. Use a Heater When Passive Methods Are Not Enough

If your greenhouse regularly drops below the temperature your plants need, a heater may be necessary. Electric fan heaters are common for small greenhouses because they are simple to use and move warm air around the space.

Place the heater in an open area where air can circulate. Keep it away from water, leaves, plastic coverings, and anything that could be damaged by heat.

Beginner tip: A heater is most effective when the greenhouse is already insulated. Otherwise, much of the heat will escape.

6. Monitor the Temperature

A thermometer helps you understand how cold your greenhouse gets, especially overnight. Place it near plant height rather than high up near the roof, where temperatures may be warmer.

A thermostat is also useful if you use a heater. It turns the heater on and off automatically, which helps prevent overheating and saves energy.

Beginner tip: Check the temperature in the early morning. This is often when the greenhouse is coldest.

7. Protect Plants on Cold Nights

Even with heating, some plants need extra protection during frost or severe cold. Horticultural fleece, row covers, or clean old fabric can help trap warmth around plants overnight.

Cover plants in the evening and remove or loosen the covering during the day so light and air can reach them.

Beginner tip: Do not let covers stay wet and heavy on plants for long periods, because this can damage leaves and reduce airflow.

8. Warm the Soil

Warm soil helps roots stay active and can be more efficient than heating all the air in the greenhouse. For seedlings and small plants, heat mats under trays are a simple beginner-friendly option.

You can also help soil hold warmth by using raised beds, mulch, dark pots, or materials such as bricks and stones around planting areas.

Beginner tip: Focus first on the plants that need the most warmth, such as seedlings, tender herbs, or young vegetable starts.

Simple Beginner Plan

1.      Seal drafts and add bubble wrap insulation.

2.      Add water containers, bricks, stones, or compost to store heat.

3.      Use fleece or row covers on the coldest nights.

4.      Monitor the temperature with a thermometer.

5.      Add a heater with a thermostat only if passive methods are not enough.

By starting with insulation and passive heat, beginners can make a greenhouse noticeably warmer without spending a lot of money. If the weather is very cold, a small heater and thermostat can provide extra protection and help keep plants healthy through winter.