Irrigation of a Large Garden

During the hot months of summer a lot of water is required to keep a large garden looking good. Fortunately Dawn Gardens has an inexpensive source of water from a canal about a mile away.

The canal delivers water to an 8” pipe through stainless steel filtering screens to homeowners in Iron Mountain Estates and to Dawn Gardens.

Dawn Gardens gets 4 miner’s inches which is about 45 gallons per minute delivered 24 hours every day from April 15 through October 15. The other days of the year we have to use well water but irrigation water is seldom used at that time. The nice thing about canal water is that it requires no pumps since it is delivered to my property in a 2” pipe at 150 psi.

This is enough to operate the entire irrigation system, the waterfalls and 10 water features at no cost except for the yearly water use fee of about $1400. When I have to use the wells it cost $600 per month in electricity costs.

Spray Irrigation

The largest irrigation heads at Dawn Gardens are these Hunter rotors which are watering the grass garden. These are turned on only once a month in the summer for 4 hours.

These rotor heads can use 4-10 gallons per minute depending on the size of the nozzle and are spaced 40-50’ apart.

The most common spray irrigation method is the pop-up spray head:

The spray head maximum diameter is 15’ and it usually has a precipitation rate of 1 1/2” per hour. In contrast, the rotors have a precipitation of about 1/2” per hour which means that you have to leave the rotors on 3 times as long to apply the same amount of water as spray heads.

Spray heads have a low trajectory so they usually have pop up nozzles so the spray can clear the foliage. But if the heads are too close to the foliage deflection will occur and plants in the back will not get enough water. Since the precipitation rate is so high there is a lot of runoff and waste.

Pop-up heads with MP Rotator nozzles have precipitation rate of 1/2″ per hour.

So bring on drip irrigation.

Drip Irrigation

80% of Dawn Gardens is irrigated by drip. It is 50% more efficient than spray or rotors because water gets to the plants and not the weeds.

Here are 2 drip emitters installed on a 1/2” PE drip line. They are dripping at the rate of 1 gallon per hour (1 GPH) and we usually install 2 emitters for each gallon size plant and water it for 1 hour 3 times per week.

If plants need more water we can install shrubblers or spectrums:

The shrubblers are adjustable and emit water from 0 to 10 GPM.

The spectrums are miniature spray heads and also emit up to 10 GPM.

All the drip irrigation in Dawn Gardens is installed on 1/2” PE tubing that is threaded through the garden and ends in end caps which must periodically flushed to rid the build up of mud solids at the end of the pipe.

Since the water comes from a canal the water has to be filtered to rid it of particles larger than 1/100” in diameter since that is the diameter of the orifice of the emitters we use. The smaller size particles accumulate at the the end of the pipe as mud or dirty water and must be flushed.

I have installed a 2” automatic filter on the pipe that comes in from the canal.

Twice a day or more it automatically flushes the wire screen filter to rid the water of algae, sand and debris.

There is a digital flow meter on the canal water pipe so we can tell how much water is being used at any particular time and the total amount of water used

Some signs that plants need water:

The grass on the left has 2 drip emitters and the one on the right has none. This photo was taken in August so the plant on the right will probably survive all year with no water but it won’t look good by October.

This is a Viburnum that is stressed because of lack of water. Notice the leaf discoloration and the burn spots in the middle of the leaves. As soon as I gave it a deep watering it sprouted new bright green leaves as you can see from the top photo.

Leaf burn on a Rhododendron after 100 degree heat

Leaf burn on Japanese Maple after 100 degree temperatures. Note the new leaves coming on after deep watering 2 weeks earlier.

Plants, such as this tree, that loose some of their leaves in the summer are under drought stress and need deep watering. It looks like part of this tree is dead but the tree is just sacrificing some leaves so the tree will live. Every year this tree does this but the next year it comes back in the spring and all the leaves are green.

This is a coring device that you can drill into the soil to see how much moisture there is at a deep level. Most mature shrubs can tolerate dryness down to 6-12”.

When the coring device is pushed into the soil and pulled out it brings out a core of soil that enables you to determine if the soil is wet or dry. Dry soil should be irrigated deeply especially in the late summer to keep the garden looking beautiful and healthy.

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