When the first warm rays of sunshine brighten up the days after the cold and dark winter in early spring, many gardeners would like to get active in the garden right away. Unfortunately, there can still be isolated frosty nights in spring, which pose a great danger to newly planted plants. This danger is particularly acute for seedlings that are sensitive to the cold and can last until the ice saints in May. The frost that still occurs at this time can be extremely dangerous, especially for very young plants, and can even lead to complete death due to frost damage. With a cold frame, the gardening season can be started earlier than usual without the disadvantageous risk of frost. At the beginning of the vegetation period, the seedlings, which are particularly sensitive to cold, are placed in an adequate cold frame.
Table of Contents
The right location
The cold frame is a shelter for cold-sensitive plants, which should thrive magnificently in spring. This can still be used in late autumn and significantly extend the harvest time by protecting the plants from frost and cold. Optimal alignment of the bed is very important so that the newly planted plants feel comfortable despite the cool days and nights.
- A very sunny area in the garden is ideal
- The cold frame should only be in the shade for a short time
- North-South orientation guarantees an appropriate and permanent sun exposure
Addition and replacement for a greenhouse
A cold frame can be a suitable replacement for a greenhouse if there is no space for it in the garden or the gardener does not have the financial means to do so. Compared to building a greenhouse, a cold frame requires a small budget.
- Cold frames replace or relieve greenhouses
- Possibility of sustainable hardening of the seedlings already grown in the greenhouse
- Perfect for very sensitive alpine and tropical plants
Cold frame to prepare for rearing
With the help of a cold frame, hobby gardeners can specifically prefer the desired fruit and vegetable varieties and flowers so that the vegetation period runs more effectively and faster. In this way there will be a large number of flowers in early spring or as late as late autumn and a richer and earlier harvest.
- Cold frame is used for pre-growing various types of fruit, vegetables and flowers
- Increasing the yield of fruits, vegetables and flowers
- The cold frame protects the plants from frosty temperatures, intense sunlight and strong winds
- Adjust the planting of the cold frame to the actual size of the garden
- There is a risk that more plants will be grown than there are suitable locations for further rearing
- Gardeners who are not technically skilled can purchase prefabricated cold frames in garden shops
- Prefabricated kits come with complete equipment and the necessary devices to protect the seedlings
- Very easy installation in the garden, which can be carried out quickly and easily
- Higher purchase price of the prefabricated cold frames
- Difficult to adapt to given conditions
- More individual and cheaper solutions offer self-made boxes for a cold frame
Building a cold frame
In principle, the cold frame is a box that is simply placed on a normal bed. A self-made cold frame acts as a greenhouse for the early cultivation of vegetables, small fruits and seeds. When built independently, the box can ideally be adapted to all the important features of the garden. However, there are a few rules to be observed so that the sensitive seedlings and plants can survive even very cold periods without damage. In our latitudes, heavy and long-lasting snowfalls are still possible at Easter, which can result in the death of many plants from frostbite.
- When building your own, first determine the appropriate size of the cold frame
- Desired number of seeds and small plants is for orientation
- When choosing a location, prefer sunny and wind-protected places with plenty of light
- Lower the walls a bit into the ground
- Countersinking eliminates bottom draft
- Material requirements: wooden boards, square timber, robust plastic foil and screws
- Plastic film serves as a cover for the outside area
- Four wooden boards for the frame and four square timbers are sufficient for small cold frames
- For larger variants, adjust the number of boards to the circumference
- Improvement of ventilation with tilting window sashes
- Screw the elements together and mount them as type cases
Preparation of the site and the plant substrate
The cold frame is mainly used in spring, when the first plants can be grown outdoors in March and the heaviest snowfalls are usually over. If the soil and cold frame have been properly prepared, even very delicate plants can thrive here properly.
- Seedlings, rich potting soil, reed or straw mats and manure
- Fill the cold frame with a layer of topsoil approx. 10 cm high
- Rich soil provides the young plants with enough minerals, nutrients and trace elements for healthy growth
- Tread the earth properly so that an even and level area is created
- Allow soil to sink for a day or two so that no air pockets or depressions remain
- Apply a thin layer of manure and distribute well, increases the supply of nutrients
- Cover mixture again with a layer of topsoil about 2-3 cm deep
- Flatten the top layer of soil again and press it down very firmly
- Leave a height of at least 15 cm at the top so that the seedlings can develop undisturbed
- Size corresponds to the ideal growth height for pricking out and weeding out the plants
- If this growth height is reached, moving to an outdoor bed is harmless
- Moving only after the last ice saints from mid-May
- Lay out reed and straw mats to protect against too hot days
Early flowering flowers and plants that react very sensitively to cold are particularly suitable for the cold frame. In the cold frame, they are always protected in the first critical months of rearing and survive even frosty nights without damage.
- Suitable vegetables: kohlrabi, pumpkins, tomatoes, lettuce, radishes
- Suitable fruit types: Common berry types such as strawberries, blueberries, currants and gooseberries
- Protection of alpine flower varieties from too much rain and the resulting rot
- Enough warmth for tropical flowers before transplanting them into the garden during the summer months
planting and planting out
So that the plants, seeds and seedlings used can thrive without any problems, correct use is of great importance. Even if the plant size is very manageable at the beginning, this factor changes very quickly and growth can become mutually blocked. If there is enough space in the soil, the plants will not get tangled up when they are pricked out later, and the rootstocks will not be damaged when they are removed
- Plant seedlings side by side with sufficient spacing
- Distance must not be too small
- Otherwise the plants rob each other of the available nutrients
- Arrange the same types of plants separately from other plants
- Roots do not get in each other’s way, even as growth progresses
- After inserting the seeds and seedlings, carefully water them to prevent them from being washed out
The care and handling
With the initial setup, the main work is done, but so that all plants in the cold frame thrive at all times, this must be under constant observation. Appropriate measures to protect the seedlings must be carried out, especially after an extreme change in weather, so that no serious damage occurs. When the plants have reached a height of approx. 15 cm, the weather conditions are playing along and no more frost is to be expected, the plants should be sorted out and planted outdoors.
- Permanently closed windows increase the risk of fatal heat build-up
- At very high temperatures, the plants die
- Depending on the weather, open the windows in the cold frame
- Sensitive seedlings and little plants need sun protection
- On particularly hot days with long exposure to the sun, cover the box with straw or reed mats
- Lay mats on the outside of the cold frame and fix them sufficiently against strong winds
watering and fertilizing
Depending on the weather, the cold frame sometimes needs to be watered more or less. In the event of heavy rainfall, watering should be suspended, as the bed is still connected to the ground and has already been supplied with enough water. If you work in a layer of manure when setting up the cold frame, the seedlings are supplied with sufficient nutrients until they are released and ultimately do not need any additional fertilization.
- Water the plants regularly, but do not overdo it
- If it rains continuously, water less or even completely
- Too much moisture leads to signs of rot
- Fertilize only if there is no manure layer and if the plants used have high nutrient requirements
diseases and pests
Due to the closed shape of the cold frame, infestation with diseases and pests can be largely avoided. The box must be closed, especially at night, so that no predatory criminals can sneak in. Nevertheless, the cold frame should be checked regularly for an infestation in order to recognize and combat it at an early stage.
- Closed shape prevents infestation with snails
- Infestation with aphids through permanently open windows
- Air the cold frame daily
- Too humid and warm air leads to the colonization of algae on the walls and windows
- Constant ventilation prevents the emergence of germs and fungi
- Never leave larger window gaps unobserved for long to avoid ravenous robbers
A cold frame extends the vegetation period of the plants and enables a higher crop yield. It can be used both in early spring and late autumn to protect cold-sensitive plants from wind and weather. In addition to vegetables and small fruits, sensitive flowers can also thrive here and delight the gardener outside of the summer months. The independent construction of a cold frame can be carried out quickly with a little manual talent and is economical in terms of acquisition costs. In addition, the box can be adapted exactly to the respective requirements in this way. The cold frame serves as a useful greenhouse and can replace a greenhouse or relieve an existing greenhouse.