Choosing & Setting Up Your First UK Cold Frame: A Beginner's Guide: Questions Answered

Question 1

Should I put my cold frame on concrete or soil?

Accepted Answer

Concrete offers excellent drainage and prevents waterlogging, which is crucial for preventing damping-off disease. You can raise the frame on bricks or paving slabs to create a level base that lets excess water escape.

Question 2

Is a south-facing wall better than a south-facing patch of grass?

Accepted Answer

A south-facing wall behind the frame provides a massive boost to heat retention compared to open grass. The wall absorbs the sun's warmth during the day and releases it at night, keeping the internal temperature higher.

Question 3

Will glass cold frames break easily in the UK wind?

Accepted Answer

Glass is heavy and rigid, meaning it can shatter if a gust lifts the frame or a stray branch hits it. Polycarbonate, on the other hand, is flexible and can absorb wind stress without cracking, though it may yellow over time.

Question 4

How much direct sunlight does my cold frame need?

Accepted Answer

Aim for at least six hours of direct sun to maximise solar gain and extend your growing season. A south-west orientation can add extra warmth in the late afternoon, while a south-east spot catches the morning sun.

Question 5

Can I use a cheap plastic mini-greenhouse as a cold frame?

Accepted Answer

Many cheap "mini-greenhouses" have raised floors and wheels, making them heavier and more prone to wind-lift than a traditional cold frame. A true cold frame sits low to the ground and has no floor, which helps with drainage and stability.

Question 6

What materials do I need to build a DIY cold frame?

Accepted Answer

You will need planed softwood timber for the frame, usually 50x50mm, and glazing such as 3mm glass or twin-wall polycarbonate. A sturdy lid with a prop stick allows you to control airflow and temperature.

Question 7

How do I stop slugs from eating my seedlings in the cold frame?

Accepted Answer

Cold frames sit low to the ground, making them a prime target for slugs and snails. You can protect your plants by placing a layer of grit or copper tape around the base of the frame to create a barrier.

Question 8

Do I need to ventilate my cold frame on cloudy days?

Accepted Answer

Ventilation is still necessary even on cloudy days to prevent condensation, which can lead to mould on your seedlings. If the lid is closed tight, moisture will build up inside and create a damp environment that harms your plants.

Question 9

Where is the best place to position a cold frame in a small garden?

Accepted Answer

The best spot is a sheltered location that maximises sunlight while protecting the frame from harsh breezes. A south-facing wall or a spot behind a hedge can provide the necessary wind protection.

Question 10

Is it worth building a cold frame if I have a greenhouse?

Accepted Answer

A cold frame is an excellent addition for hardening off plants and extending the harvest by four to six weeks. It provides a low-cost, low-profile way to protect seedlings without the commitment of a full greenhouse.

Question 11

What is the best angle for the lid of my cold frame?

Accepted Answer

The lid should be angled to catch the maximum amount of sunlight throughout the day, typically facing south. This ensures that the interior remains warm and the plants receive adequate light for photosynthesis.

Question 12

Can I put a cold frame on a patio or decking?

Accepted Answer

You can place a cold frame on a patio, but you must ensure the surface is level and provides good drainage. If the decking is permeable, water will drain away easily, but if it is solid, you might need to raise the frame on bricks.