Pounding hollow aluminum footings into the newly leveled ground before setting up the frame of a new processing greenhouse. This greenhouse is not intended for in-ground growing, so the site has been graded with gravel to make the ground as level as possible. (Photo Source: Acadia Tucker).

This past spring, I moved from southern Maine to a small town way up north. Here, I had the unique opportunity to explore the ins and outs of kelp farming in Frenchman Bay’s cold, clean waters.

Aquatic plants, like kelp, pull carbon from the atmosphere in the same way as terrestrial plants grown in soil. But kelp, and other seaweed, is more efficient—it doesn’t need potable water, arable land, or pesticides to grow. Kelp farms also work to improve local water quality and ocean habitat. In short, it’s a spectacular regenerative crop, and I jumped at the opportunity to participate in this year’s growing season.

Before harvest kicked off, we built an ambitious drying greenhouse to handle the soon-to-be bumper crop. While patrolling the farm, we saw giant sugar kelp blades over 15 feet long! We gathered the right tools, read the instructions repeatedly, and hired a bobcat to level and grade the area before construction began.

I love the versatility of greenhouse structures—be it on a commercial scale or in your backyard. Greenhouses are commonly used to protect crops during cold weather or keep pests away all summer. But, they’re also helpful for processing, seeding, and storing equipment.

Greenhouse kits give you an excellent running start on your project, or you can, of course, make one yourself. We decided to go with a 30 by 96-foot Rimol Gothic Greenhouse kit. We landed on this style because the tall ceiling was perfect for hanging long pieces of kelp. The straight 10-foot sides also meant more headroom for walking, and the pitched roof would protect the greenhouse from heavy snow. It took about two months to build between our other farm tasks, with the extra muscle of my Co-worker, Nick. 

We ran into a glitch or two. Typical for rocky New England soils, we struck a granite ledge while driving the support footings into the ground and had to drill through the rugged rock. On the Maine coast, sudden winds created unwelcome delays when covering the greenhouse with plastic. Challenges aside, greenhouses are a nice addition for any gardener looking to level up their growing game.  

Greenhouses come in all shapes, sizes, and materials, making any choice overwhelming.

The right shape. Allow your local weather to determine the right shape. In the snowy Northeast, I benefit from gabled or pitched roofs with narrowly spaced roof supports that quickly shed snow, and support added weight. If you live in a warmer climate, you’ll be fine with a hoop or rounded greenhouse with wider gaps between roof supports, which are often less expensive.

The right size. Choose a size that suits the activity. Nurturing seedlings will require less space, for instance, than growing full grown vegetables.

The right materials. Look to your micro-climate for guidance. Rigid polycarbonate plastic panels do better in windy areas than soft polyethylene plastic films, which can become tattered at high wind speeds. Glass and fiberglass options are heavy and durable but come with a high price tag. If you're stuck, consider talking to a greenhouse manufacturer for guidance.

Once you’ve decided on the best shape, size, and material for your greenhouse, it’s time to get building.

I learned, the hard way, the value of positioning my greenhouse on the calm side of a building, fence, or hedge row—to help buffer strong winds. I recommend removing hazards like tree limbs that have the potential to fall and cause damage. Most importantly, orient your greenhouse so it faces south or southeast, to maximize your light.

An example of what not to do: The first greenhouse I built was not situated in a protected location, which exposed it to sudden Nor’easters like the one that caused the damage shown here. Always build greenhouses in sheltered areas. (Photo source: Acadia Tucker)

If you’re considering a few possible locations, I recommend taking soil tests at each one. Look for soil that test high for fertility plus offer a blend of sand, silt, and clay. Don’t fret too much if your tests show low fertility, high clay levels, or sandy soils. All it means is you’ll have to condition the soil over time by using compost and regenerative growing practices, like cover cropping, to help build loose, fertile ground.

Another, sometimes easier option, is to fill your greenhouse with raised beds. These allow you to start fresh with hand-picked, well-aerated soil. You can purchase bulk compost-based soil from your local nursery or make your own with sheet mulching techniques. Growing in raised beds is handy if your site’s soil conditions are poor or contaminated.

Finally, consider locations close to water, so it’s easier to irrigate. Also, consider efficient locations close to tools, electricity and storage, especially if you're constructing a propagation house for seeding pots and planters, which need extra care and attention.

The completed frame of the processing greenhouse. It will need some reinforcement before it’s covered, but so far, it’s standing sturdily on this carefully gravel-graded site. (Photo Source: Acadia Tucker)

I tend to rush this step because I’m eager to get to the building phase, but site preparation is essential and will come back to haunt you if not done right.

First, you want to make the footprint of your greenhouse as level as possible. This can mean bringing in soil to even out, grade the area, or dig deep to level the site. Larger structures may need additional site work, like a permanent foundation of poured cement or stacked cinder blocks to provide extra support. 

We decided to add a leveled base of gravel for our kelp greenhouse. A gravel base is highly counterproductive if you plan to grow directly in the ground. However, our goal was to create a sturdy, mud-free platform for our processing and, in winter, allow us to store boats and equipment.

Most greenhouse kits come with a parts list, a required tools list, and instructions. The most versatile greenhouses are made from bent aluminum purlins or rods that you attach with metal screws and bolts to form hoops. Other framing materials can include various metals, woods, or plastics. In my experience, most instructions take a few read-throughs to visualize, so be patient and do your best to follow along step-by-step.

To build an aluminum frame, start by driving the hollow metal footings into the ground at least two feet deep, if not more. The footings anchor the rest of the frame and prevent the greenhouse from taking flight once it’s covered with plastic. Space the footings equally along the length of the greenhouse and as straight, level, and square as possible. If your greenhouse does not come with footings, I recommend buying a kit of anchors or cement weights to secure the frame once it’s built. 

When it’s time to build the frame, set yourself up for success by enlisting the help of a few friends (unless you choose an itty-bitty greenhouse). It’s especially nice to have help when raising the metal hoops, and attaching bits of frame above your head or from a ladder. 

Add extra hardware to shore up the structure once the bulk of the frame is up. We attached long wooden boards to connect the metal hoops for extra stability. Other options include adding additional supports for the roof, like trusses to support the weight of snow. Finally, double-check that all hardware like screws, bolts, and hinges are secure and fully fastened before taping over any sharp bits that could rip the plastic before you start the covering process.

The inside of the newly covered processing greenhouse. Notice the wooden planks added for reinforcement, so the structure will be sturdy, and the frame reinforced during strong winds. (Photo source: Acadia Tucker)

If you go with a soft plastic covering, choose a nice calm day to raise it. Large sheets of plastic are unruly even in slight breezes. The goal is to stretch your cover as tightly as possible over the frame—think saran wrap over a bowl of leftovers.

This part is tricky. I avoid punching holes or creating stretch marks in the plastic by using my forearm (rather than my hands) to apply downward pressure as I wrap the cover over the frame. Here's a helpful video to walk you through the process. 

Other materials, like glass or rigid plastic panels, come with their own set of installation instructions. You’ll either need to frame them, like a window in a home, or drill through the material to fasten them to the frame. 

Greenhouse kits have so many additional accessories it's impossible to mention them all. From temperature-controlled vents to roll-up sides to trellising systems—the list of extras is long. The greenhouse we made is designed explicitly for drying kelp; notice the tarp on the ground for sweeping up between batches with a shop broom. We also installed a custom trellis to support the weight of the drying seaweed. It takes time and experience to know exactly how to customize your dream structure.

The finished processing greenhouse is being used to dry kelp here. With time and experimentation, I figured out that laying a tarp on the ground allows for easy clean-up and transition to the next processing round. With time, you’ll learn little tricks like this to make your growing process easier. (Photo Source: Acadia Tucker).

So that’s the general workflow. Things will never go as smoothly or quickly as you wish, so give yourself plenty of time, be patient with yourself and your team members, and keep the end goal in mind: a high-quality, productive greenhouse that will serve your growing purposes for years to come.

Acadia Tucker is a regenerative farmer, climate activist and author based in Maine and New Hampshire. She’s the author of three regenerative gardening books.

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