Last week we installed a system of misters over the propagation bench for seedling germination.

Last week's project was installing misters over the propagation bench

Most of the vegetable starts will be transferred directly from the propagation bench, to the garden, so most of our seedlings won’t need anything more elaborate in the way of a watering system.

Vegetable seedlings like these beets don't spend long in the greenhouse

However, many native plant seedlings, woody perennial plants, and grafted fruit trees, will be held in the greenhouse until the plants are substantially larger, potentially for a number of months at a time.

Newly grafted fruit trees may spend a year or more in the greenhouse

We also occasionally dig up plants in the gardens to relocate them, or acquire plants at native plant sales, that may not immediately find their way to a permanent location in the garden.

This young Ceanothus 'Dark Star' may spend a number of months in the greenhouse before being planted out

As such, a number of these larger container plants will need a reliable source of water during their stay in the greenhouse.

The challenge with watering container plants in the greenhouse though is that irrigation systems can quickly transform into a tangled mess of tubing, and it can be challenging to design a system that is flexible, efficient, and can accommodate enough plants at once.

To help keep the watering system for the potting bench organized, and as tangle-free as possible, we’ve elected to go with a type of irrigation system more commonly seen in commercial nursery greenhouses.

As with the mister installation, for the transplant bench we used one-half inch irrigation line, which we’ve attached to a piece of rigid PVC to help keep it flat to the bench top.

At the water inlet, again because we irrigate with well water, we’ve installed a screen filter to minimize particulate accumulation in the emitters.  This is the same setup we used for the greenhouse misters.

The system starts with the pressure regulator, and a screen mesh filter

This particular system uses an over-sized pressure compensating dripper head that is installed directly into the half-inch water line.

The tapered red end is inserted into a hole punched into the 1/2" main water line tubing

The manufacturer also offers a flexible cap that can be installed to cap off each emitter if not in use.

The emitter cap slips around the base of the emitter as it's installed

It’s easier to install the caps at the time the emitters are seated in the tubing.

The cap is held in position on the emitter during installation

Even though we’re also installing shut-off valves in this drip line, we’re not sure yet how our greenhouse may evolve over time, so we opted to install these caps so they’re there if we need them in the future.

Installed emitter with cap

Once the central emitter and cap are installed, the dripper assembly can then be snapped onto the emitter.

For this system we’re using multi-outlet dripper assemblies.  There are two types of assembly for this system, and which one you use depends on how many individual drippers you want to supply from an emitter.  Each emitter can supply up to sixteen dripper stakes (in multiples of four stakes per assembly). We determined that eight 1 gallon containers per emitter should suffice for this application.

The first dripper assembly supplies water to four dripper lines.

This assembly has four separate dripper lines, and the center is open to supply water to a second assembly above

The center of the assembly is open at the top to supply water to additional dripper assemblies installed above it.

The second assembly adds four more drippers, but is sealed at the top.

The stacking nature of these dripper units helps to prevent a tangle of tubing across the bench top, keeping the lines tidy, and together in one place, and this is what attracted us to this system in the first place.  If lots of smaller containers need water, we can install additional assemblies on each emitter to expand the system.  If just a few large plants need irrigation, we can remove the bottom assembly, and just use four drippers on the emitter.  Each stack can be easily installed or removed as needed throughout the season.

This system should be able to shrink and grow through the season depending on how many plants need water

In between each emitter/dripper unit we installed half-inch shut-off valves (which we’ve now also added to the mister setup installed last week).

The black water line is simply cut anywhere a shut-off valve is needed

The ends of the valve are then pushed into the line and secured

This gives us a tremendous amount of flexibility during the season.  We can turn mister or dripper assemblies off during the year that aren’t being used, which will keep the bench tops drier, and prevent wasting water.  The valves may seem redundant as we also installed the emitter caps, but the shut-off valves stop water flowing to ALL the dripper assemblies downstream of the valve.  However, if we need to restrict water only to emitters in the middle of the water line, we can cap those off, and still preserve flow to the drippers at the end of the run.  This should minimize the need to modify the system later.

Turning the control perpendicular to the water line shuts off all water to any drippers below that valve

At the moment, any dripper units that are shut-off simply hang down below the slats in greenhouse bench to minimize clutter.

Dripper lines not in use hang below the bench, keeping the bench-top relatively uncluttered

As we’ve installed these units in a single straight run, if we need the bench space, and have no plants being watered on the transplant bench, we can simply slide the entire watering assembly to the back of the bench out of the way.

To supply water to individual containers, each white dripper line terminates at a rigid built-in dripper stake.

The dripper stakes are built in to each piece of 1/4" tubing

The water emerges through holes in the stake and simply runs down into the root zone.

Water flows down each stake into the pot

Multiple stakes can be used in large containers as needed.

These plants are waiting to be transplanted outside

This new system should not only us save time, and water, but also help to ensure the plants get the water they need, where they need it, without being over or under-watered.

This buckwheat is currently blooming in the greenhouse, and is not fond of getting its leaves wet

It also keeps the water off the leaves of more sensitive plants like this Rosy Buckwheat (Eriogonum grande var. rubescens).

The dripper lines are all clustered down the center of the bench, leaving plenty of room for plants

With both the mister and dripper systems now installed in the greenhouse, we can finally start germinating some of our favorite native plant seeds we’ve collected from around the property.  I suspect we’ll be spending lots of time in the greenhouse this winter!