The Tunnette
a DIY mini tunnel for starting seeds in your backyard
Starting seeds doesn’t need to be complicated, you just need: good soil, an effective way to water, and a proper shelter to keep your plants protected. DIY is the way to go because you can make something to the specifications of your space, and desired volume of plants.
When I first started farming in 2023, I used this exact method to start a quarter-acre’s-worth of starts in my backyard and didn’t yet have a greenhouse. I grow everything from transplants, so that was a lot of plants, and it had to work!
Lets take a moment to explore the alternatives. The first things that comes to mind when I think of home seed starting is the windowsill and those 4-level racks enclosed in plastic. They are common ways to begin a seed starting journey and unfortunately they are both problematic.
Even the brightest windowsill doesn’t provide the full sun that seeds need to grow robustly, not leggy (grow lights are another story, but that is not my area of expertise). The rack has potential, but how about watering? Won’t water drip from one level to the next, possibly disturbing germinating seeds? And because of its height, it can be top-heavy and is often positioned against the wall of a building, again limiting the potential for full sunlight.
The mock-up in the photos holds 4 standard trays (1020 dimensions) which translates to 200-800 plants.
4 x trays with eight 6-packs each = 198 plants
4 x 72 cell trays = 288 plants
4 x 128 cell trays = 512 plants
4 x open flats with 200 plants each = 800 plants
… and that a relatively small tunnette. The tunnette is also nice because it can be taken apart when not in use rather than being a permanent fixture in the yard. Winter storm damage to a seeding station is a real thing!
Alright, lets build!
Tools and Materials Needed:
2x4’s/ scrap lumber/ a pallet
drill and impact driver
3.5” deck screws
76” row cover hoops
clips
greenhouse plastic/ row cover/ insect net/ bird net
crates/ cinder blocks to elevate the frame
string or strapping of choice, in windy locations
Step #1: Build your frame. There is no need for a central cross support. Width should be just wider than your trays, like .5-1” on each side, to allow for the hoops. Length is determined by how many trays you want to start a once and how much space you have. You can also go double wide, just add center pieces of wood every 8-12 inches.
I used 2x4’s, but other scrap wood can work. Two deck screws at each corner. If your wood is very dry, pre-drill holes. For fresh lumber, you may be able to go straight in without pre-drilling. If your trays are at all saggy, add one more piece of wood down the middle. I’ll also note that you can fasten hardware cloth to the top of the wooden frame, but it isn’t necessary.
Step #2: Drill holes for the hoops using a drill bit just a tad bigger than the hoop. Use row cover hoops, 10 pack here. The row cover hoops are worth getting, as they can be installed right into holes you drill into the wood. Push the row cover hoops through the holes. It will be longer than needed to form an adequate hoop, so extend the wires past the bottom of the frame (once elevated, pictured in the photo after step 3) or trim to a desired length— 52 inches is closer to the hoop size you’ll want if making your tunnette wide enough for one tray.
Alternatively, use half inch flexible PVC. If using PVC, you will need to use galvanized pipe strap like this to attach it. You want one hoop at each end, and hoops down the length of the tunnette every 2-3 feet.
Step #3: Raise your frame at least a foot off the ground. Use plastic crates, milk crates, cinder blocks, or anything else you have laying around. You can also build legs to make it a more formal table, but in that case you will need a stronger frame/ tabletop.
Step #4: Choose a cover. This will keep birds, and other surprise predators away from your baby plants! Your material choice will be informed by the season and how frequently you can monitor. Greenhouse plastic is best for cooler weather, as it gets quite cozy in there. You can use plastic in warm weather, too, but you need to ventilate during the heat of the day, so this only makes sense if you are home. Row cover keeps critters out without getting as hot as plastic. Bird net will keep birds out, but not insects. For the hottest areas, I recommend insect net and a placement that gets morning sun, afternoon shade.
Step #5: Secure your cover. Use clips/ clamps to fasten it directly to the wood, or tuck under your trays (best with row cover). Use additional clips to bunch material together at openings of the tunnette, as there will be excess here. Wind is the enemy here, so your clipping, tucking and clamping needs to hold up to your strongest afternoon gust.
(as needed) Step #6: Heavy duty hold downs. Diagonal strapping can be really helpful if you are in a windy area. I used bailing twine.
If you want something with built-in strapping, there are low tunnel hoops designed just for this. I have something called Kwik Hoops, but they don’t currently seem to be available online. Here is an alternative. These offer a little more security and are a bit more aesthetically pleasing. The hoops can also be used elsewhere in the garden, so the investment is for more than a singular use.
Additional Notes and Considerations
Tunnette Placement: Above grass or soil invites slugs and other critters to venture up from below. All the watering will also make grass grow a lot, so it is not recommended unless it is the only option. (My tunnette was over grass, and it was a pain). If you do place it over grass, be ready to move it and mow regularly. Ideal placement is over a deck/ cement/ a piece of weed mat stapled into the ground under and around the tun.
Watering: The tunnette is out in the elements. Wind and heat will dry things out. Remove cover and water at least once daily during germination, and monitor water needs once plants are up. If you are away from home for many hours a day, look into bottom watering. Also, it is so worth having a hose + nice watering wand. Watering cans and sprayers that blast water can disturb soil and hinder seed starting success.
Wind: Use clips and clamps to hold your cover down. Secure your chosen cover material to the wood, and also to the hoops. In especially windy areas, wrap bailing twine or strapping of choice diagonally across the tunnette.
Slugs: They happen. They love moisture and wood. Just use some Sluggo. You’re going to so much effort to raise your own seedlings. Don’t chance it!