Extending your garden’s growing season doesn’t have to break the bank. Cold frames offer a cost-effective way to cultivate spring greens or fall crops well beyond when exposed plants typically falter. The best part? You can construct them using items you likely already have lying around, eliminating the need for significant upfront investment. Furthermore, cold frames don’t require a sprawling landscape to be effective – a compact space will do just fine.
In this comprehensive guide, we’ll delve into the ins and outs of building and utilizing these ingenious structures in your own yard.
Is it Greenhouse, Hothouse or Cold Frames?
While the terms cold frame, greenhouse, and hothouse are often used synonymously, they actually serve distinct purposes. A greenhouse typically refers to a more substantial structure, traditionally composed of glass or plastic supported by a wood or metal framework, evoking an image of a house-shaped building with transparent walls that one can walk around in.
A hothouse, on the other hand, is a type of heated greenhouse commonly employed by horticulturists to cultivate exotic plants such as orchids. Modern farms have also adopted hoop houses, which are essentially tunnels formed by attaching plastic sheets to metal hoops, used to protect and nurture crops.
What Is a Cold Frame?
A cold frame is a unique structure that creates an ideal environment for plant growth by providing warmth, shelter, and protection from outside stressors. Its design features low walls made of materials like glass, plastic, or straw bales, with a translucent top that allows sunlight to enter. This microclimate within the frame warms the interior temperature, shielding plants from wind, frost, and extreme weather conditions.
By creating an optimal environment, you can extend the growing season for your plants, allowing them to thrive longer than they would otherwise. The purpose of using a cold frame is to offer supplemental protection to plants during specific stages of their growth cycle. You can utilize cold frames alone or in conjunction with a greenhouse, as I do by placing them on the south side of my greenhouse to provide a gentle transition for seedlings.
One notable advantage of cold frames over greenhouses is that they require less watering, as the plants are planted directly in the ground, reducing the need for frequent irrigation. Additionally, cold frames generate their own humidity, which can be beneficial for plant growth. However, it’s essential to monitor your plants on sunny days, as the structure can become too warm and retain excess heat.
To address this, you’ll need to raise the lid or top to allow heat to escape, ensuring a healthy and balanced environment within the frame.
Some things that cold frames are great for:
When it comes to nurturing seedlings, getting the right start is crucial. For those emerging from the greenhouse, hardening off is essential to ensure a successful transition to outdoor conditions. Meanwhile, warming up the soil before planting can be just as important for optimal germination and growth. In the spring, giving lettuce the best possible beginning can lead to a bounty of fresh greens.
As the seasons shift towards fall, covering kale plants can prolong the harvest and provide a longer window for enjoyment. Furthermore, sowing spring greens early on can jumpstart the growing season, while overwintering tender plants in zones 7-10 offers a unique opportunity to coax them through the cold winter months.
Making Cold Frames
Cold frames are an accessible and budget-friendly DIY project. As a mentor for young women interested in sustainable agriculture, I typically introduce this simple yet effective method early on. Alternatively, you can purchase pre-made cold frames online, ranging from basic to elaborate designs. The beauty of building your own lies in the flexibility to adjust the size according to available materials.
Ideally, the back of the frame should be slightly taller than the front to create a slope that allows rainwater to run off and permits sunlight to enter. When constructing your cold frame, consider repurposing reclaimed materials like cement blocks, scrap wood, or salvaged windows and glass doors for the sides and roof respectively.
Just keep in mind that if you live in an area prone to heavy snowfall, it’s essential to either use sturdy materials or design a steeply angled roof to prevent snow accumulation from causing damage.
Cold Frame Designs
While there are various types of frames available, each with its unique benefits and drawbacks, it’s worth noting that every DIY version has its own set of advantages and limitations too. From my perspective, here are some DIY cold frame designs that I find particularly appealing.
Straw Bale Cold Frame
Straw bale frames are a personal favorite of mine, and for good reason. Their insulating properties make them ideal for fall and winter crops. Building one is surprisingly easy – simply form a square or rectangle using 4-6 bales of straw. To provide additional protection from the elements, cover the straw with old windows, storm doors, or plastic sheeting. Manual ventilation will be necessary, achieved by opening a window or removing it for the day.
I place my straw bale cold frames directly in the garden, selecting a spot that’s been cleaned and tilled. Before planting fall and winter crops, I’ll often clear the area of unwanted pests using my chickens as a natural cleanup crew. Typically, this process begins in September for me, given my zone 6 location.
To prepare for the cold weather, I start seeds for fall in one of my barn sheds during late summer to prevent them from getting too hot.
Once the cold frame is set up and ready, I transplant seedlings into the soil. At this point, I only need to open the lid on extremely cold nights. As the weather cools, it becomes part of my evening routine to adjust the lids and protect the plants.
I usually enjoy greens from my cold frames until January, at which point my season comes to a close due to having consumed all the produce rather than the cold itself.
When spring arrives, the rotting straw can be repurposed as mulch or added to the compost pile. It’s worth noting that hay isn’t suitable for cold frames due to its high weed seed content.
Pallet Cold Frame
Pallets, a budget-friendly building material, offers a straightforward approach to constructing cold frames. Their simplicity is what makes me appreciate this type of project. To build this particular design, the creators disassembled the pallet and used its individual boards. A frame was then constructed using 1-by-2-inch lumber pieces, forming a box shape. Two old windows, hinged for easy opening, complete the top. The angled design allows for maximum sunlight exposure.
This template is versatile enough to accommodate various modifications, making it perfect for early spring greens or hardening off seedlings. With this basic structure, you can explore other DIY options and create what suits your needs.
Amish Style Cold Frame
The concept of this cold frame design originates from the Pennsylvania Dutch, who brought their European roots with them when they immigrated. Its innovative features include a triangular ‘roof’ and hinges that cleverly optimize space and accessibility. The cover can be constructed from plastic on both sides or feature plywood on one side for enhanced insulation. While this design excels in many ways, its main drawback is that it may be more cumbersome and heavier than other options.
When building the triangular top, you have two choices. One approach is to create a separate unit that can be lifted off to ventilate or harvest your crops. Alternatively, you can hinge the top so it lifts up for easy access.
Using Your Cold Frame
Eliot Coleman, renowned for his expertise in cold frames, highlights their significance in his book ‘Four Season Harvest’. He asserts that the fundamental cold frame is a dependable and underutilized tool for year-round harvesting. Notably, many gardeners assume they must choose between a cold frame and a greenhouse, but this dichotomy can be misleading. In reality, these structures can work harmoniously together to offer an array of growing options.
The key to maximizing your space lies in strategic planning. During the early spring months, you can utilize a cold frame to initiate salad seedlings, while reserving your greenhouse for plants requiring extended germination periods or warmer temperatures. For instance, you could start onions or tomatoes in your greenhouse, as they thrive in these conditions. When cultivating spring greens, a cold frame offers a distinct advantage by providing a protected environment and genuine sunlight.
Unlike artificial lighting, which can lead to leggy growth, direct sunlight fosters healthy, robust plants. Moreover, the portability of a cold frame allows you to relocate it once your greens have matured and the weather has warmed. This flexibility enables you to continue growing other crops in the same space.
Ventilation
The ability to easily lift and ventilate the lid of your cold frame is crucial. On sunny days, allowing heat to escape prevents overheating, while in winter, it prevents the frame from warming up too quickly and damaging your plants. One simple solution is to prop the lid open with a piece of wood for ventilation. Alternatively, you can install hinges on the sides, allowing the roof to swing open like a window or door, eliminating the need for propping.
For added convenience, consider investing in automatic vent openers from greenhouse companies. These temperature-activated devices will automatically open the lid when the interior reaches a certain threshold, perfect for busy days. If you prefer a more manual approach, keeping a thermometer inside the cold frame provides valuable insight into your plants’ needs and helps ensure proper ventilation.
Overwintering Tender Plants
For gardeners living in zones 7-10, a cold frame offers an excellent solution for overwintering tender plants that might not thrive during harsh winter conditions. This protected environment enables plants to enter dormancy, ensuring they’re ready to flourish when spring arrives. If your garden layout permits, you can place the cold frame directly over your existing plants.
Alternatively, transplant them by cutting back the plant as recommended for its species, gently lifting the root ball from the soil, and potting it in a large container filled with insulation-rich potting soil and sufficient water. To optimize space, pack multiple pots closely together, separating them with leaves or straw to maintain insulation and minimize watering needs throughout the winter. A layer of white sheets on top will help regulate temperature and suppress leaf growth.
I’ve found that cold frames have revolutionized my gardening experience, extending my growing season and giving me an early start for spring planting. Their simplicity and cost-effectiveness make them a hard-to-beat choice.
