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Head Start:
Seed-Raising Box

Place your box in a sunny spot and near water.. Photo by Robyn Rosenfeldt

Successful seed germination requires three important things: warmth, light and moisture. With some recycled timber, you can create the perfect seed-raising environment.

As we wait for the soil to warm up this time of year, there are many places around our homes well suited to raising seeds for spring planting. The goal is finding a place which is nice and warm to promote germination and protect your young seedlings from the elements, but still with plenty of light to guide the new shoots to the surface.

A sunny indoor windowsill offers both warmth and natural light, but it’s when we start adding the third important element – water – that raising seeds indoors all of a sudden becomes a little less appealing. There are many commercially available outdoor options, but with a little bit of nous and some recycled materials, you can make a seed-raising box perfectly suited to your needs.

What You’ll Need

It doesn’t matter what you use as your lid, as long as it’s transparent enough to allow plenty of light in, while being airtight enough to trap the warm air beneath it. Because it’s likely to be the most difficult piece to source, decide on what you’re going to use as your lid and work backwards to make the rest of the structure fit its size.

You’ll need enough planks of timber in order to create the sides and the base of the box for your seed trays to sit in as well as the shelf beneath. You’ll need some sturdy timbers to create the frame for the box to sit on, some extra planks to brace it, as well as hinges for the lid and appropriate screws and tools to piece the whole thing together.

Ensure the box is deep enough to allow for good growth. Photo by Robyn Rosenfeldt

Plan Your Build

Start by measuring your window, if you want your lid to fit flush on the top of your box, these measurements will be the external dimensions of the box. Prioritise the nicest timbers for the front and set aside the roughest pieces to use as the base and rear of your box which won’t be seen. Measure and cut the planks to the appropriate length, not forgetting that the side pieces of your box need to be shortened by twice the thickness of your timber to account for the front and rear planks. When deciding on the depth of your box, consider how tall your healthy seedlings may be rather than the height of your seed-raising trays. Depending on the width of your planks, you may need two or even three boards to achieve an appropriate depth.

Piece It Together

To construct the box, screw through the ends of the long sides to join to the end pieces. If you’re using hardwood, it’s a good idea to drill small pilot holes where your screws are going in order to prevent the timbers from splitting. Decide which side is the bottom and, using the same technique, screw the base timbers onto the box before drilling half a dozen or so drainage holes in the base to allow excess water to escape.

Flip the whole thing over and lay your window on top of your newly made box before screwing two hinges onto both the side of the box and the edge of your lid. While you’ve got your timbers and tools handy, cut a length that you can use to prop your lid open while you’re seeding or adding and removing trays.

At this point you can decide to place your seed-raising box on a sunny outdoor table or propped up on bricks, or you can choose to carry on and build the frame.

Plan The Frame

Building a frame sturdy enough to cope with the weight of both the box and the damp soil that will inevitably be inside it is more complex than just screwing four legs to each corner. Work out a comfortable working height and, using sturdy timbers such as old fence rails, cut four pieces that will form the legs. Now measure the width of your box from the back to the front, and cut four more pieces to that length, these will form the support for your shelf at the bottom – as well as extra support for where your legs meet the base of the box.

A simple length of wood is all you need to create a prop for access and airflow. Photo by Robyn Rosenfeldt

Build The Legs

Take the timbers that will form the front and back legs of one side of your frame and screw one of the supporting timbers across the tops, to sit flush with what will be the top inside edge. Screw another length of the supporting timber across the same two pieces, this time towards the bottom of the legs. This rail will support the lower shelf. Decide how low you want the shelf to sit. You may even want two, in which case add a third rail. Repeat the process for what will form the front and rear legs of the other side of the box before screwing each set of legs to the base of the box. By screwing from the top of the box down into the legs and their supports, you won’t get any sharp screws poking through into your box.

Bracing The Build

With nothing to brace sideways movement, at this point the legs of your box will be susceptible to movement, so work carefully. As well as providing storage space, the shelf offers lateral bracing to your build, so screwing your planks onto your support rails will offer more stability than simply sitting them on top. Moving to the back of your build, close in the rear of your frame by screwing planks across the back of the legs. As well as giving it a finished look, this will increase the lateral bracing of your seed-raising box and ensure its longevity for many planting seasons to come.


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