Milk Jug Greenhouse - A How To Guide - Our Happy Backyard Farm

Using a milk jug greenhouse is a great DIY project and will help you get a jump start on your summer garden.

Each year sometime in February or March, we’ll have what I call False Spring. The sun will shine, the birds will sing, and it will seem like summer should be right around the corner. It will seem like a great time to start planting a few things. Not so fast! Unfortunately, False Spring will show up for a few days and then the temperatures will plummet again.

a milk jug greenhouse cut open to show the tomato seedlings

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But one way to get the most out of those warmer days is to get a jump start on your summer garden with some milk jug greenhouses.

These little, recycled greenhouses are the perfect no fuss method to getting some seeds up and going.

With just a few items you’ll be well on your way to growing some beautiful and hardy seedlings to add to your garden after that last frost date.

Items Needed For Milk Jug Greenhouses

Empty Milk Jugs – rinsed and dried – you do not need to keep the lid

Box Cutter or a Sharp Knife

Duck Tape

Potting Soil

Seeds

Spray Bottle

Permanent Marker

Directions For Making Milk Jug Greenhouses

First, let’s get the milk jugs ready. Take your empty milk jugs and rinse them thoroughly to get any milk residue out of the bottom. Then place them upside down to drain. Throw away the lid – you will not need it for your greenhouse.

Using a box cutter or sharp knife, cut the milk jug about three quarters of the way around. I start my cut about 3 inches or so from the bottom of the milk jug. I do not cut under the handle. This will keep that section of the little greenhouse more sturdy if you need to move them for any reason.

Next, we’ll cut some holes in the bottom of the milk jug. This will allow for drainage. The water needs to be able to drain so that our little seeds and seedlings don’t become waterlogged. I typically cut four or five little holes.

Fill the bottom of the milk jug with dirt. The dirt needs to be about 2 inches or so deep. This will allow for the roots to get a great start in the milk jug before you transplant them into your garden space. There are a variety of soils to choose from at your local gardening store. I just buy the potting soil and have always had success. But feel free to try something different and let me know how it goes!

Now it’s time to plant the seeds! By far my favorite part – let’s get those seeds in the dirt! The seeds do not need to be planted way down deep in the soil. If you plant them too deep, you’ll never see them again. As a general rule of thumb, you’ll want to plant the seeds at a depth that’s about twice the width of the seed. So, if your seed is about 1 mm wide, you’ll want to make the hole about 2 mm wide. Most seeds are pretty small – much smaller than a millimeter – so be aware of that when planting them.

After the seeds are planted at an appropriate depth, spray them with water. It’s nice to have a spray bottle to do this, so you don’t drown your seeds. The soil should be damp, but not soggy.

Tape up the cut around the milk jug. Use a generous amount of duct tape to do so. You want to create a nice seal so that the cold air is not getting to your plant through this cut. Having a good seal also helps create the greenhouse effect we’re wanting.

Use the permanent marker to date and label your milk jug greenhouse. Every year I think I’ll remember what I plant, when and where, but I just can’t. I need to label everything.

Now it’s time to set your milk jug greenhouse in a nice sunny spot. Pick a place where it’s not likely to be knocked over or in the way of other activities. I usually just put mine somewhere in the garden.

Wait and watch. This is the fun part and the hard part! It’s always so exciting to watch a little plant miraculously burst through the soil. So much hope, determination, and new life packed into one teeny, tiny seedling. You’ll get the joy of watching this tender little plant grow and get stronger with each passing day.

Another thing to watch for is moisture. After a couple of days you should see water droplets forming along the sides of the milk jug. This is a great sign the greenhouse effect is happening. As the water evaporates from the soil it will cling to the sides of the milk jug and then fall back into the soil. This wonderful water cycle will keep your plant hydrated with minimal effort on your part.

close up of the inside of a milk jug greenhouse

Working in the dirt on a sunny day (even if it is just False Spring) is a great way to chase away the winter blues and anticipate the excitement of a new growing season.

FAQs and Tips For Milk Jug Greenhouses

What if I don’t see any water droplets?

If you don’t notice any water droplets on the sides of your greenhouse after a few days, you need to spray the soil with water. Do not open the duct tape (we want to keep that tight seal), just spritz some water through the opening at the top of the greenhouse. Because we discarded the lid, the opening at the top of the milk jug will also catch rain water. Rain water is by far the best water for growing plants.

What if my seeds don’t grow?

Unfortunately, there could be a variety of reasons that seeds don’t grow. And sometimes gardening is just trial and error. Some tips for getting seeds to grow well, is to make sure they are in a great environment. Not too wet and not too dry. Not too hot and not too cold. And also make sure you are getting seeds from a reliable source.

How cold is too cold for the milk jug greenhouses to be outside?

One of the great things about these recycled greenhouses is they are able to withstand some cold. We live in zone 6b. I typically start my milk jug greenhouses between mid February and early March. There’s still a possibility of snow during that time. My milk jug greenhouses have survived snowy days. The greenhouse effect traps warm air around inside the milk jug helping your little plants thrive even on cold days.

When can I transplant?

Most seed packets will give you a time frame for this. It’s usually around 6 – 8 weeks after planting. You want to make sure you don’t transplant until after the last frost date. Around here that’s Mother’s Day weekend!