Key Takeaways -

• Mini greenhouses are perfect for small spaces like balconies, patios, and compact gardens.
• Choosing the right materials, location, and ventilation is key to successful plant growth.
• DIY options include cold frames, hoop houses, and upcycled structures using old furniture.
• Regular maintenance, insulation, and space optimisation help maximise plant health and yield.

A mini greenhouse is a great way to grow plants in small spaces while protecting them from harsh weather. Whether you have a balcony, patio, or small garden, the right greenhouse can extend your growing season and keep your plants healthy.

This guide will cover the different types of mini greenhouses, from simple cold frames to DIY wooden structures. You’ll also learn how to choose the best location, materials, and tools. Step-by-step instructions will help you build a greenhouse that fits your space and needs.

Keep reading to find out how to create a small greenhouse, whether using repurposed materials or building one from scratch. No matter your experience level, you’ll find practical tips to maintain it and keep your plants thriving all year round.

Different Types of Mini Greenhouses

Cold Frame Greenhouses

Cold frames are small wooden structures with a glass or plastic lid. They trap warmth, making them ideal for extending the growing season and protecting plants from frost. These are easy to build using scrap wood, old windows, or clear plastic panels.

Cold frames work well for growing hardy greens, starting seedlings, or sheltering plants inside during colder months.

Hoop House Greenhouses

Hoop houses are made from flexible PVC pipes and covered with plastic sheeting. They are lightweight, easy to move, and perfect for temporary plant protection. These greenhouses can be built over raised beds or placed directly on the ground.

They provide warmth and humidity, helping young plants grow faster. Ventilation is key—lifting the plastic or cutting small air holes prevents overheating.

Wooden Frame Greenhouses

A wooden frame greenhouse is a sturdy, weather-resistant structure made from treated timber and covered with polycarbonate or glass panels. It offers better insulation and durability than plastic-covered options.

Though more effort is required to build, it provides a long-term solution for gardeners wanting a reliable growing space. These greenhouses can be custom-built to fit patios, balconies, or gardens.

Upcycled Greenhouses

Upcycled greenhouses repurpose old materials like windows, bookshelves, or storage racks. They are a budget-friendly, sustainable option that can be adapted to fit any space. For example, an old bookshelf wrapped in clear plastic can become a mini greenhouse for seedlings.

These structures work well in urban gardens where space is limited, but creativity is key.

Planning Your Mini Greenhouse

Choosing the Best Location

A south-facing spot gets the most sunlight, helping plants thrive. Avoid placing your greenhouse in shaded areas or where buildings block the sun. Shelter it from strong winds to maintain warmth and prevent damage.

Accessibility is also key—position it near a water source where you can easily check on your plants. If space is limited, consider a compact design that fits on patios or balconies.

Selecting the Right Materials

Choose a frame material that suits your budget and durability needs. Wood (pine or cedar) is sturdy, while PVC pipes are lightweight and flexible. For covering, options include glass for insulation, polycarbonate sheets for durability, or clear plastic sheeting for affordability.

Don’t forget essentials like hinges for access, screws for stability, ventilation holes for airflow, and weatherproof sealant to protect against moisture.

Essential Tools and Supplies

Basic tools like a measuring tape, saw, drill, and screwdriver are needed for assembly. Hinges allow for easy opening of lids or doors, while screws secure the structure. To protect wooden frames from moisture and decay, apply paint or a weatherproof wood stain.

If using plastic or polycarbonate panels, ensure you have a strong adhesive or sealant to keep them in place.

DIY Step-by-Step: How to Build Your Own Mini Greenhouse

Building a Wooden Cold Frame Greenhouse

A wooden cold frame greenhouse is a durable, space-efficient option for small gardens. It uses a wooden base and a transparent lid to create a warm, protected space for plants. This design works well for seedlings, cold-hardy greens, and extending the growing season into early spring or late autumn (1).

1. Construct the Wooden Frame: Measure and cut wood to your preferred dimensions. Assemble a rectangular base using screws or nails, ensuring a solid foundation. Add vertical supports at the corners for extra stability, especially if using heavier materials like glass or polycarbonate.
2. Install the Transparent Covering: Attach a clear material such as glass, plastic sheeting, or polycarbonate panels to the top of the frame. Secure it tightly with screws or brackets and apply silicone sealant along the edges to prevent heat loss and moisture buildup.
3. Add a Hinged Lid for Ventilation: Attach a recycled window or a lightweight polycarbonate panel to the top using hinges. This allows for easy access and proper ventilation. On warm days, prop the lid open with a stick or install a simple latch system to regulate airflow and prevent overheating.

Making a PVC Hoop House Greenhouse

A PVC hoop house greenhouse is an inexpensive, lightweight, and flexible structure. It provides excellent protection for young plants and can be moved or adjusted as needed. This type of greenhouse is great for temporary plant shelters, season extenders, or even as a protective cover for raised beds.

1. Build the Frame Using PVC Pipes: Create a wooden base or position the greenhouse directly over a raised bed. Insert flexible PVC pipes into the frame, bending them to form an arched tunnel. Secure them at both ends to maintain their shape.
2. Secure the Plastic Covering: Stretch clear plastic sheeting over the PVC frame, making sure it covers the entire structure. Attach the plastic securely using clips, zip ties, or heavy-duty staples. Pull it tight to prevent sagging, which can trap moisture and reduce insulation.
3. Ensure Proper Ventilation: Cut small air holes along the sides to allow airflow and prevent overheating. On warmer days, lift the plastic covering or use weights and clips to hold it partially open. Proper ventilation helps prevent mould, mildew, and excessive humidity inside the greenhouse.

Alternative DIY Mini Greenhouse Ideas for Small Spaces

If you're short on space, upcycling everyday items into simple greenhouses is a creative and sustainable solution. These DIY ideas are budget-friendly and can be adapted to fit balconies, patios, or small gardens.

Bookshelf Greenhouse

Turning an old bookshelf into a mini greenhouse is a simple and cost-effective way to create a warm, protected space for plants. With a few modifications, you can transform it into a functional growing area for herbs, vegetables, or flowers.

1. Cover each shelf with clear plastic sheeting and secure it tightly with zip ties to trap warmth.
2. Cut small ventilation flaps into the plastic and use clothespins to hold them open when needed.
3. Add foam insulation boards to the sides to maintain temperature and shield seedlings from cold drafts.
4. Place in a bright spot indoors or outdoors to maximise sunlight and encourage plant growth.

Window Frame Greenhouse

Repurposing old windows into a greenhouse is an eco-friendly way to create a sturdy and stylish growing space. This upcycled design provides excellent insulation while adding character to any garden.

1. Attach three windows together to form the side and back walls, securing them with screws for stability.
2. Use hinges to install a front-opening window as a door, allowing easy access to plants.
3. Position two windows at an angle to create a slanted roof that maximises sunlight.
4. Replace old glass with horticultural glass to improve heat retention and create a more efficient growing environment.

Wine Box Greenhouse

A wooden wine box can be transformed into a small, efficient greenhouse perfect for seedlings or delicate plants. Its compact size makes it ideal for windowsills, balconies, or garden tables.

1. Remove one end of the wine box and cut slanted edges to create a pitched roof.
2. Install shelf supports inside using leftover wood strips to add multiple growing levels.
3. Attach acrylic sheets to the front and top with glue and small hinges to create a sealed light-filled space.
4. Place in a sunny spot to provide warmth and protection for young plants.

Keeping Your Mini Greenhouse in Top Shape

Temperature Control

Proper ventilation is essential to prevent overheating, especially on sunny days. Open vents, prop up lids or cut small air holes to regulate airflow. In winter, use bubble wrap or horticultural fleece to insulate your greenhouse and retain warm air inside.

Positioning it in full sunlight ensures maximum warmth, helping plants thrive even in colder months.

Watering and Humidity Management

Monitor soil moisture closely to avoid overwatering, which can lead to root rot. Ensure your greenhouse has proper drainage holes to prevent water buildup. On humid days, increase airflow by slightly opening doors or vents to reduce excess moisture and prevent mould growth.

Keeping humidity levels balanced creates a healthier growing environment for your plants.

Preventing Pests and Diseases

A clean greenhouse reduces the risk of mould, mildew, and plant diseases. Regularly remove dead leaves and debris to prevent fungal growth. Use fine mesh or netting to keep insects out while maintaining airflow. Rotating plants helps prevent disease buildup and keeps the soil healthy.

With proper care, your greenhouse will remain a productive space for growing strong, healthy plants.

Frequently Asked Questions

Can I Build a Mini Greenhouse Without a Garden?

Yes, you can build a mini greenhouse even if you don’t have a garden. Compact designs like tabletop greenhouses, vertical shelving units, or repurposed bookshelves work well for balconies, patios, and even indoors near a sunny window.

Using clear plastic covers or polycarbonate panels helps trap warmth while allowing light in. Proper ventilation and drainage ensure healthy plant growth in small spaces.

Can I Use My Mini Greenhouse for Year-Round Gardening?

Yes, but plant selection and insulation are key for year-round gardening in the UK. Hardy greens like kale, spinach, and winter lettuce can survive colder months with minimal heating. Adding bubble wrap insulation, fleece covers, or a small heat source can help maintain stable temperatures.

In warmer seasons, ventilation and shading prevent overheating inside the greenhouse.

What’s the Best Way to Maximise Space Inside a Cold Frame Greenhouse?

To maximise space in a cold frame greenhouse, use vertical growing techniques and compact plant varieties. Stackable containers, tiered shelves, or hanging planters help make the most of limited space. Position taller plants at the back and shorter ones at the front to ensure even sunlight exposure.

Regularly rotating crops also keep the greenhouse productive year-round.

Can I Grow Fruiting Plants in a Mini Greenhouse?

Yes, fruiting plants like strawberries, dwarf tomatoes, and peppers can thrive in a mini greenhouse. Choosing compact or bush varieties helps save space while maximising yield. Training vining plants like cucumbers to grow vertically on trellises further optimises limited room.

Proper pollination, ventilation, and warmth are essential for healthy fruit production.

What Materials Should I Avoid When Building a Mini Greenhouse?

Avoid untreated wood, as it can rot when exposed to moisture. Low-quality plastic may degrade over time, becoming brittle and ineffective for insulation. Heavy glass panels should be used with caution, as they can make the structure difficult to move and may pose safety risks.

Instead, opt for treated wood, polycarbonate panels, or UV-resistant plastic sheeting for durability.

Conclusion

Building a mini greenhouse is a practical and rewarding way to grow plants in small spaces. Whether you choose a cold frame, hoop house, or upcycled design, the right materials and setup will help you create a thriving environment for your lovely plants.

Regular maintenance, proper ventilation, and smart space management ensure long-term success. With the right approach, your mini greenhouse can extend your growing season and provide fresh produce year-round, even in the UK’s changing climate.

Start building today and enjoy the benefits of homegrown plants in any season.

Sources -

1. https://www.gardenary.com/blog/how-to-make-a-diy-cold-frame-or-mini-greenhouse