See the first of the series: Planning #1 - to Begin.

The next step is all about drippers. How many and which type?

Often a home drip irrigation circuit includes trees, flower beds and a few shrubs, an assorted mix of plant types, each requiring a different amount of water each day. By choosing the dripper rate of flow and the number of drippers, we can irrigate both trees and flowers on the same circuit.

Example

A small tree may need two gallons of water per day and an annual flower may only need 1/4 gallon. We can combine both plants on one circuit. (See the Wizard to learn how much water is needed by different plants)

We'll use a one-half gallon per hour dripper (D45) for the annual flower and turn the system on for 30 minutes each day so that the annual gets exactly 1/4 gallon per day.

We'll use two drippers (D5) for the tree at two-gallons per hour to deliver the two gallons the tree needs in the 30 minutes the system is on each day.

The more water the plant needs, the more drippers we use and/or the higher the rate of flow for each dripper.

Dripper sizes

We stock drippers in one-half, one, two and four gallon per hour rates of flow.

Choose the best quality dripper you can afford. They will last longer and perform more consistently than lower grade drippers. All the Pressure Compensating drippers we stock are agricultural-grade from Netafim and extremely reliable.

Start with the smallest

If your drip circuit has only trees of the same size, you could use any size dripper and simply vary the operating time to get the amount of water required. But in most cases, there are mixed plant types on a circuit and you should start planning with the dripper rate of flow and watering time for the smallest plant. Then simply choose drippers for the larger plants that can deliver the right amount of water in the same amount of time.

If you have a group of plants that need a lot less water than normal, consider adding an inline valve to the supply line so that you can adjust the flow to those drippers.

Soil types

Soils range from sand to loam to clay. When wet, sandy soils will not hold shape when you squeeze it tight in your hand. Loam soil will form a ball when squeezed but the ball will fall apart easily when handled. Clay soil will form a tough sticky ball when wet and will form an oozing ribbon when pressed hard.

Sandy

Water moves quickly down through sandy soils due to all the open spaces between the sand particles. Capillary action is weak and water does not travel horizontally as far as with other soil types. Alter the wetting pattern by using a higher rate of flow. You might substitute a two-gallon per hour dripper for a one-gallon per hour dripper.

Clay

Water moves down slowly through clay soil which has much smaller particles and a slower rate of capillary action. But the capillary action is strong and water tends to move horizontally just under the surface rather than down past the root area. Alter the wetting pattern by choosing a dripper with a low rate of flow. Or turn on the system for multiple short periods rather than one long period of time.

Most garden soils have a mix of sand and clay and the pattern of capillary action is closer to the ideal which is a neat globe pattern of water surrounding the root area. Dig down after watering to observe the wetting pattern.

Maximum time

In most cases, we want the drip irrigation system to turn on for no more than 60 minutes per cycle. The reason is that gravity pulls the water down into soil below the root area after 60 minutes and additional water is wasted. The exceptions are deep-rooted plants and trees. A test dig after watering is the best way to determine how deep the water is going.

Pressure Compensating

If your drip irrigation system is on level ground, you can choose any available dripper. If your system in on rolling ground or hillsides or if it includes hanging baskets, choose a pressure-compensating dripper (PC dripper). On hillsides, there is more water pressure at the bottom of the hill than at the top. Pressure-compensating drippers have a small plastic diaphragm that keeps the flow of water the same no matter the pressure of the water. PC drippers will deliver the same amount of water to the plants at the top of the hill and to the plants at the bottom.

What not to include

Not all plants need irrigation. Many slow-growing shrubs need so little water that the occasional rain is enough. Large trees have roots down so far that they have all the water they need in any weather.

If you want to limit the growth of a plant, exclude it from your drip irrigation circuit. Shrubs and trees often start new rapid growth when switched from the occasional hand watering to consistent drip irrigation.

Drip is best suited for plants that must grow quickly without stress and produce the most foliage, flower or fruit.

Next in the Planning series is Planning Your Drip Irrigation #3 - Locating Drippers