Elevating the seasonal growing game with cold frame gardening

Grow vegies for longer with cold frame gardening. Pictures: Hannah Moloney.
Grow vegies for longer with cold frame gardening. Pictures: Hannah Moloney.

Cold frame gardening

We built a much anticipated, beautiful bit of infrastructure for our garden - a cold frame.

This is a welcome addition to any cool temperate garden, where we're all constantly working on creating warm microclimates to extend our season to get tomatoes earlier and longer, reliable eggplants and abundant basil.

CLEVER: Cold frame gardening is a technique to help extend the growing window of some vegies. Pictures: Hannah Moloney.

CLEVER: Cold frame gardening is a technique to help extend the growing window of some vegies. Pictures: Hannah Moloney.

Cold frames can be really compact and small, so are also a great option for people who don't have a large enough space for a hot house or polytunnel.

We built our cold frame from green (fresh) hardwood timber and polycarbonate sheeting.

We located it up against a north facing rock wall so it soaks up the hot sun and acts as thermal mass, retaining the heat for longer to benefit the crops growing in front of it.

More lifestyle:

Things to know about building garden beds with hardwood

  • Eventually hardwood will rot - but not for around 10 years (approximately).
  • If you can access it and afford it, cypress macrocarpa timber is the most durable timber to use in the landscape. We couldn't afford it, so used a mix of eucalyptus trees.
  • To extend the timber's lifespan, you can line the sleepers with non-toxic plastic to prevent direct contact between the timber and soil. While not shown in the photos, this is what we did.
  • We've built the frame so the timber sleepers can be removed and replaced as needed.
  • The actual frame has separate timber pickets on each upright to stabilise the whole frame.
  • Eventually we'll replace these with steel star pickets - again to extend the life of the frame.
  • You could use bricks or stone instead of timber for the edging and steel for the frame with concrete footings - all maximum durability. We used what was available to us.

Soil prep and planting

Once the whole frame was built we aerated the soil with a broadfork - you can just use a standard garden fork if that's all you have.

Beautiful eggplants. Picture: Hannah Moloney.

Beautiful eggplants. Picture: Hannah Moloney.

After this aerating process, we put down a layer of cardboard to slow weeds coming back (they will come) and then a good layer of top soil around 200 millimetres deep to match the height of the sleepers and a sprinkle of compost on top.

And then it time to plant. Normally, where we are in Tasmania, we plant our tomatoes in late October.

Traditionally this is when you can safely say there'll be no more frost - although occasionally there'll be a "freak" frost.

But our cold frame allowed us to plant a small batch one whole month earlier - it gave us big smiles on our face in anticipation of eating tomatoes sooner rather than later.

So many tomatoes. Picture: Hannah Moloney.

So many tomatoes. Picture: Hannah Moloney.

We also plant basil seedlings all around these tomatoes to make use of all the available space.

Importantly, the lids can open at different heights to let small or large amounts of air in. This is important as on hot, sunny days you need to ensure that air flow is maintained, otherwise there's the risk of fostering fungal diseases.

As we get really strong winds at our house we put a lock on each lid. One year our whole broccoli crop was literally blown out of the ground - so we take our wind-proofing pretty seriously around here.

Eating with the seasons is a wonderful way to eat.

That first tomato of the season tastes really amazing after six months of no fresh tomatoes.

But this little bit of infrastructure reduces that waiting time - some might call it cheating, we just call it clever.

  • Hannah Moloney and Anton Vikstrom are the founders of Good Life Permaculture.