How to Over Winter Plants in an Unheated Greenhouse

Overwintering is the practice keeping plants indoors during the winter.

 

This is typically necessary when a foreign plant is unable to survive the local climate.

Gardeners are often able to overwinter their plants in an unheated greenhouse, although this may require additional protective measures for plants in especially cold climates.

Overwintering generally requires the gardener to bring plants into the greenhouse during the late fall and take them back outside in the spring.

 

A greenhouse is generally any structure specifically intended for growing plants, and is covered by a clear material that retains heat.

Plastic and glass that is specifically intended for use in greenhouses is commercially available.

These materials allow heat from the sun to enter the greenhouse and prevent it from escaping outside.

A greenhouse is typically much warmer than the outside environment, even when it does not have an artificial source of heat. An unheated greenhouse is often sufficient for over wintering plants.

 

The primary purpose of over wintering plants in an unheated greenhouse is to keep the plant alive, without necessarily allowing it to flourish.

These plants often remain in their dormant phase while in the greenhouse.

An unheated greenhouse may also be used to start plants early, so they can be planted after the last expected frost of the winter.

This type of greenhouse can also prolong fall gardening past the first frost.

 

Plants that require over wintering typically enter a dormant phase during which they shed their leaves and stop growing, although they are still alive.

Plants generally enter their dormant phase when the temperature or light level drops below a certain point in the fall.

Gardeners usually wait until the plants are well into their dormant phase before moving them into the greenhouse.

A plant that is still actively growing is less likely to survive the trauma of being moved.

 

 

Gardeners typically water plants just before being moved.

Moist soil takes longer to freeze and dry soil will provide additional protection, while moving them into the greenhouse during cold weather.

Container plants can simply be carried by hand into the greenhouse.

Plants that are growing in the soil outside will need to be transplanted.

This generally involves digging up the plant without cutting the root ball and planting it in an indoor container.

 

 

The plants being overwintered in an unheated greenhouse will need protection from the cold.

This generally requires an enclosure to be built around the plants.

Pound stakes into the ground around the containers with the plants, ensuring the stakes are secure.

Cut a section of chicken wire with tin snips.

The length of the section of chicken wire should be a few inches longer than the diameter of the circle described by the stakes, which will allow the chicken wire to overlap itself.

The height of the chicken wire should be greater than the height of the tallest plants you plan to enclose. Wrap the chicken wire around the stakes, leaving it open at the top. Secure the chicken wire in place with staples or wire.

 

This enclosure will allow you to cover the plants with dead leaves, which will protect the plants with insulation from the cold.

Ensure the leaves completely cover the branches, as even slight exposure to the cold can kill the plants.

Gardeners in very cold climates may also need to provide plants in an unheated greenhouse with a frost cover.

This is a sheet made from a material such as polyester.

It must be thin to allow light to reach the plants, but also insulated to protect the plants from cold.

A frost cover is typically placed over supports so that it doesn’t come into direct contact with the plants.

 

The watering of plants is a critical factor in overwintering plants.

Plants generally require much less water when they are in their dormant phase.

It is especially important that the soil not remain wet while the plant is in its dormant phase, as this can cause the roots to rot.

Some plants will benefit from occasional water that keeps the soil moist, while others need just enough water to keep the soil from drying out completely.

 

Overwintered plants should generally be moved back outside during the early spring while they are still dormant.

Gardeners must also wait until the date of the last expected frost has passed.

The last frost date for a particular area is commonly available from almanacs, nurseries and other gardeners.

It is also important to monitor weather reports for any forecasts of late frosts when selecting a specific moving date for the plants.

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