Yesterday, while it was cold and raining outside, I spent a few hours inside the greenhouse putting together part of our new irrigation system for the propagation bench.

The greenhouse propagation bench (click any image to enlarge)

Over the last 20 years I’ve installed countless drip irrigation systems in our gardens, and the gardens of family and friends.  No two systems have been the same, but this is the first time that I’ve had the opportunity to set up a system for a greenhouse, and it’s our own greenhouse, so that makes it even more exciting.

To make the best use of the benches in the greenhouse, we need a reliable method for watering the plants

Our greenhouse will be used primarily for seedling propagation.  Much of the kitchen garden is planted successively with crops throughout the spring and summer.  The vast majority of those plants are started from seed, and sown in flats or plug trays.

Most all of our vegetables are grown from seed

Once large enough the young plants are transplanted into the garden.

Once the plants develop a healthy root system, they're either potted into larger containers, or transplanted into the garden

Only a few crops, primarily some of the root vegetables such as carrots, are direct-sown in the garden.  Everything else will spend at least some time in the greenhouse.  This helps to minimize damage to the seedlings from hungry birds, and slugs, when the plants are most vulnerable.

Even as the kitchen garden winds down, during the fall and winter months, that doesn’t mean we’ll run out of plants in the greenhouse.  Propagation of woody cuttings, and some native plant seeds, will occur during the months when the food gardens are less busy.

The weather here in winter is generally more wet than cold, so it’s likely there will always be something growing in the greenhouse throughout the year.

One challenge was deciding how to organize the greenhouse to be the most efficient for our needs.

Before installing any irrigation, all of the greenhouse benches were first sealed to resist water

We installed plenty of bench space for seed starting and propagation, but the plants also will need regular water.  Even during a warm sunny winter’s afternoon seedlings can dry out very quickly, and dragging a hose through the greenhouse is cumbersome.

We’ve chosen to devote one long bench specifically to seed propagation, and the other for propagating cuttings, and potting on transplants.  Each bench, however, will need a different watering setup.

Individual drippers set into pots are fine for cuttings and more mature plants, but seedling propagation usually requires a more even distribution of moisture across the entire soil surface to ensure even germination.

It's important to keep the soil evenly moist when germinating from seed

For the propagation bench we’ve chosen to go with an overhead mister system.

Each mister is composed of three pieces that can be easily disassembled if they become clogged

Preassembled kits are available from various vendors of greenhouse irrigation supplies, but as we use a lot of drip irrigation components all around the farm, we chose to put together our own so we could use materials we already had.  We just needed to purchase the actual mister assemblies for this project.

Assembled mister fitting

The misters need to be suspended above the seed trays at an even height across the bench.  As the rafters of the greenhouse are too high to attach the misters to, we first constructed a simple stand to suspend the misters from.

In large setups, trellis wire can easily be used to support the misters, but we wanted something more flexible, and portable, in case we need to rearrange the greenhouse during the growing season.

We’re using PVC pipe for the stand, and chose not to glue any of the fittings, so if not required for a time, the stand can be dismantled and stored flat.

The irrigation system doesn't weigh much, so a lightweight PVC stand is more than sufficient

This simple stand consisted of 20 feet of 1/2-inch PVC, two 1/2″ slip-elbows, four 1/2″ slip-T fittings, and six 1/2″ inch end caps (to prevent dirt getting inside the ‘feet’).

A few simple tools are all that's needed. Clockwise from left, pruners (to cut the irrigation tubing), a tape measure, tubing hole punch (to install mister fittings), and a PVC pipe cutter

An 8 foot length of pipe was cut in half, and a 1/2″ PVC slip-T positioned in the center for a middle support leg.  An entire 8 foot length of 1/2″ PVC is likely to sag over time without some support in the middle.

To save your hands, it's worth investing in a quality hole punch, and replacing the punch tips when they become dull

A 1/2″ elbow was fitted at each far end, and attached to a 24″ section of pipe to form the vertical support legs.

A simple slip-slip elbow connects the horizontal support to the legs at each end

For stability, an additional slip T was placed at the bottom of each leg to hold two 12″ horizontal supports to prevent the stand from tipping forward or backward.

A slip-T fitting was used at the base of each leg to hold the feet

With the stand constructed, the next step was to cut 1/2″ drip irrigation flex pipe to fit the stand.

Starting at the far end, we attached a threaded drain end-cap to the end of the 1/2″ flexible water line.

This end cap seals the far end of the water line, but the threaded cap can be removed to flush the line

This will allow us to flush the system through should one or more of the misters become clogged.

We cut a section of 1/2″ tubing the height of the stand, and to prevent too much torque at the ends of the pipe, we fitted the ends with 90 degree locking elbow connectors.

These fittings have threaded 'locks' at each end, that clamp against the water line, preventing blowouts under pressure

As we have very high water pressure here, we always use locking connectors on 1/2″ tubing runs.  The elbows will help the pipe to lay flat against the stand, and will ensure the tubing doesn’t twist, and knock the misters out of alignment.

The elbow holds the tubing flat against the stand, and prevents the line from kinking

The next length of tubing ran the entire 8 feet across the top of the stand, connected again at the opposite end through a 90 degree elbow.

Zip ties secure the water tubing to the stand. These ties are UV resistant as they'll be exposed to a lot of sunlight

The flexible water tubing was secured to the stand, loosely at first, using zip-ties.

The water line (black) was run parallel to the stand (white), and fitted loosely with zip-ties until the misters were installed

Holes were punched into the tubing using a 1/8″ hole punch at each point along the tubing where a mister assembly would be installed.  The misters were positioned 16″ apart to ensure even coverage above the seed trays.  This is where attaching the water line to the stand loosely at first helps.  If the line is too snug, it makes it difficult to position the punch around the tubing.

The hole punch is positioned to pierce the UNDERSIDE of the tubing, as the misters will hang below

The mister assemblies we chose were selected specifically because they have an anti-drip device, that prevents dripping on the plants after the misters are turned off, as persistent dripping can lead to seedling damage.

The tip of the mister assembly is pushed into the hole punched into the water line

Once the misters were installed down the length of the tubing, additional zip-ties were installed to secure the 1/2″ water line securely to the stand.

Because of our high water pressure we fitted the water inlet with a pressure regulator to ensure even watering, and prevent the misters from being blown off the line.

At the water inlet end of the line, a pressure regulator was installed

Also, as we irrigate with well water, we placed a fine mesh particulate filter after the pressure reducer, but before the first mister assembly, to prevent the misters from clogging.

A particulate filter was installed after the pressure regulator, but before the misters (blue arrows show direction of water flow)

One pending addition to the system, as soon I pick up the parts, is to insert a few 1/2″ shut-off valves along the length of the water line, between some of the mister assemblies.  This will enable us to turn the water off to selected misters, and leave others on, if the benches aren’t completely filled with seed trays, giving us more control over watering.

Once the water was connected we could test the misters (note to self, move the camera BEFORE turning the water on)

The permanent mainline PVC irrigation pipes won’t be installed up to the edge of the greenhouse until our soils soften up a little more in the garden from the rains.  That’s one of our tasks for this winter.  For now we’re temporarily running the misters using a standard hose end connection.  Once the rigid permanent water lines are installed though, the 1/2″ main waterline will be permanently installed, and connected to an irrigation control valve, and timer, so seedling irrigation can be automated, and adjusted throughout the growing season.

Now the mister system is installed, we'll never dry out our seedlings too much again!

The temporary hose hookup though will eliminate the need to hand water the seedlings in the meantime, freeing up more time for other projects…and we seem to have no shortage of those at the moment.

In our next greenhouse irrigation post, we’ll be setting up a new (to us) irrigation system on the rear bench in the greenhouse to water transplants, and potted plants, but first…I have some seed sowing to do!