Create Your Own Mini Greenhouse

Create Your Own Mini Greenhouse

In the process of deciding how best to support my morning glories and moonflowers as they grow taller, I came up with an idea for a fun, cheap, and easy DIY garden project: making mini greenhouses from domed lid cups… inspired by a pot roast.

Yes, really.


My Pot Roast Suggested It…

Pot Roast
Mmmmm…… Pot Roast!!

A few weeks ago, I was planning a pot roast for my husband and I to enjoy over the weekend. I went to the store to get what I needed, and I found these little “bio-domes” of herb cuttings that, according to the package, kept the herbs fresher longer. They were stuffed full, too. A little pricey at $3.99 per dome, but I was intrigued and having ideas of my own.

I bought one each of rosemary and thyme, and along with some little multi-colored potatoes, carrots, onion, garlic, and chuck roast, we had a delicious pot roast all weekend long.

I kept the two bio-domes full of the leftover herbs in the refrigerator, as per the instructions, and I thought there must be something else I could do with these. “These little bio-domes look like mini greenhouses, and… HOT DOG!!” Just like that, I had the perfect do it yourself gardening project.


Mini Greenhouses

I did a little research on propagating herbs, many of which are easily grown by rooting directly in water, and I decided I would try to make these mini greenhouses out of what I had. It went like this:

  • Sorted the herbs to keep the longest, greenest remnants and discarded the rest.
  • Stripped the leaves from the bottom inch of each remnant.
  • Wrapped the remnants in a folded paper towel to keep them together and upright, secured with a very loosely bound cable tie.
  • Filled each cup with an inch of water.
  • Placed each herb bundle in its cup and attached the lid.
  • Placed the cups in a bright windowsill out of direct sunlight.

Nothing happened for a while, but I was so sure this was a good idea that I bought a package of 100 16 oz. plastic cups and dome lids on Amazon. I waited anxiously for the results of my experiment.

16 oz. Cups with Dome Lid

A few tips about this process:

Being that the paper towel is wrapped around the plants, you can’t see what the roots are doing, but per my research, it takes a good two or three weeks for the herbs to start rooting. What you watch for is growth on top. If your plants are getting taller, you’re in good shape. As they get taller, they have a little hole in the dome lid to climb out of and keep them upright.

Also be aware of the issue of mold.  My herbs were sitting in water.  As a result, it developed some fuzzy mold on one of the plants that didn’t make it. You don’t want to be growing mold in your little greenhouse, but it won’t hurt your plants, and sometimes it’s just unavoidable. I was able to just wash that off of the plant that was growing well, remove the dying, moldy bits and keep going.  Under normal growing conditions, mold is a sign that you are overwatering.


Water Levels:

Generally speaking, you won’t need to add much water, if any, during this process. The little dome lid keeps the moisture in very well, even with the hole in the top, however, the paper towel soaks up a lot when you first put your little plant bundle in.

Make sure you have enough water in the cup to cover the stripped leaves on your herbs after the paper towel soaks up its fill. If you have to add a little water during the waiting time, that’s fine and easy to do. I poured a little bit directly in the top of the dome lid so I didn’t have to disturb the plant.

After two to three weeks, I was seeing regular growth at the top of the plants and took them apart to see what kind of rooting activity was taking place. Not much, really, but you don’t need much. I decided to move to the next phase of the greenhouse.

Greenhouses - Mint, Herbs, StrawberriesNext Phase: Potting Soil

Time to experiment again. I took my herbs, and along with some chocolate mint roots (that root VERY well in water), and a couple of overly ripe strawberries, planted a half dozen mini-greenhouses.

First, I made eight tiny holes in the bottom of each of six cups. These need to be able to drain very well to prevent mold growth and waterlogging. I wrote on each cup with a permanent marker what would be in it and the date. Masking tape also works well for this.

Next, I filled each cup about two-thirds full with moist potting soil, pressing it gently but firmly into the cup.

Then, I took a small wooden dowel rod and poked holes in the soil – as many as I needed for each plant. (Four holes in one cup for four rosemary stalks, one for my one thyme sprig, two each for the mint).

For the strawberries, I filled the cup about one-third of the way with potting soil, planted one strawberry each in two cups with the green leaves down, berry pointing up. I filled in another third of the cup with soil and gently pressed the soil firmly around the strawberry.

I placed each plant in its hole (you can squeeze the water out of the paper towel into the cup and toss the paper towel).

Lastly, I filled each cup with water, placed the dome lids on, and let excess water drain out of the tiny little holes I had poked in the bottom of each cup.

Watering these can be a little tricky because you don’t want to disturb the plants in the soil. I held mine mostly submerged in a gallon pitcher of water and allowed the water to filter up through the holes from the bottom.  You can water them from the top, but keep the flow very light.

So, what happened?

My thyme and rosemary are back in their places on the windowsill, and the thyme is growing up and out very quickly. The rosemary is also growing well, just not as fast. The mint is growing, but I can tell that I probably should have planted one stalk each in a cup. They are already competing for space.

I don’t know what the strawberries are doing. If the seeds germinate, it will likely take a good while before sprouts appear. This was a true experiment – no idea what to expect. If something happens, you’ll be the first to know. Well, after me. And my husband. Okay, you’ll be the third to know.


Advantages and Disadvantages of the Mini Greenhouse

I loved this idea from the start, being as easy and as cheap as gardening projects can be, but I wasn’t sure how it was going to turn out. I was concerned about the prospect of mold growth in a mostly closed off, moist environment, but it occurred to me that most of the plants we buy at nurseries come in plastic containers. The only differences are, they don’t come with lids, and they are not see-through. So, here’s the low-down on what’s great about this system and what isn’t:


    1. Protection: Protects plants and soil from drying out too fast during development, and the dome lid provides support for growing plants.
    2. Conservation: Conserves water, but it’s easy to add water from the top or bottom if/when necessary.
    3. Ease of Use: Clear cups allow you to see what’s happening beneath the surface, so it’s easier to tell when a plant needs water, is ready to be transplanted, or when it gets root-bound.
    4. Sustainability: Re-use your frap cups from Starbucks, etc. – buy one frap, get a free mini-greenhouse! Re-usable again after you transplant!
    5. Inexpensive: You can get a hundred or more from Amazon in various sizes for less than $20
    6. Quick and easy: This DIY gardening project takes less than five minutes for each mini greenhouse!


    1. Size: Footprint is kinda big. You’ll need a place with plenty of light and something underneath to catch water drainage.
    2. Mold Potential: Can be prone to mold growth – Don’t overwater. The mold will not harm your plants, but it is a sign that they are too wet.

As you can see, the advantages far outweigh the disadvantages of this system, but I’m still experimenting with it, so I’ll keep y’all posted.


Video Instructions

Ready to try this quick and easy garden project for yourself? Please take a few minutes to watch my instructional video on YouTube. Like I said, each one takes less than five minutes! The video shows me transferring peat pellets to the little greenhouses, but it would be very easy to substitute any little plant or to plant seeds directly.


As always, please let me know if you have any questions in the comments.

Until next time,
Stay healthy and safe!
Bunny & Greg
The Grey Gnome

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