July 2002

GROWER 101: Irrigation Practices By Carrie Burns

It doesn’t matter if your operation is large or small,new or old, if you grow annuals or perennials, or if you are affected or notaffected by the drought; irrigation is a critical, yet sometimes overlookedpractice. It can save you money and, after considering the recent precipitationproblems, protect you from a disastrous drought.

So, what do you need to know about irrigation? According toLaura Pottorff, regional commercial greenhouse specialist at the Colorado StateUniversity Cooperative Extension, these three steps can help you utilize waterproperly with the minimum amount of waste. The first step should be implementedby all greenhouses wherever feasible. The second is better but more expensive,so it should be executed when financially possible. And the third is ideal.

Step 1: Reduce Runoff

To reduce wasted water and/or runoff, try to group plantswith similar water needs. Then, apply 10-15 percent more water than thecontainer will hold, and don’t allow water to flow over the top of thecontainer. Consider which media is best. Some of the organic constituents usedin growing media have hydrophobic or water-repelling characteristics. Unlessthese are absolutely necessary, try to avoid using them.

Step 2: Embrace new irrigation technologies

This step gets a little more expensive than the last, butsavings on your water bill is worth it in the end. It also ensures that anadequate supply of high-quality water will be available when it is neededduring production. Subirrigation systems, whether ebb-and-flow, flood-floor,trough or capillary mat, are the most efficient water users. Though they arevery expensive to install, they require less fertilizer than overhead systems,and they allow foliage to remain dry. Drip or trickle systems also work well,providing good control over the amount of water applied.

Step 3: Collect and reuse irrigation water

The third step is the most expensive and complex of thethree, but the benefits over time make it worth the investment. Retentionbasins, storage ponds, storage tanks and additional pumping capacity are usedfor this. Make sure local regulations allow for holding ponds or for reusingirrigation water. With any form of recycling, many problems can arise: forexample, harmful pathogens or impurities can contaminate the water and damageyour crop. But this can be overcome by careful monitoring.

Monitor salts, chemicals, nutrients and pH. Dilute high-saltwater with fresh water. Or, use reverse osmosis to remove harmful salts.

Become proactive when dealing with water-born pathogens.Scout problem crops more often; remove diseased plants right away; monitorpathogen levels of irrigation water by taking samples to plant disease testinglaboratories; and treat water for disease organisms by retention and dilution,filtration, chlorination, ozonation and/or UV light.

Find what’s best for you

Every greenhouse has different financial and physicalsituations, so complete reuse may not be possible. Put into effect what you canand what is right for you. Maybe even purchase water wise products/equipmentover time; they will pay for themselves in the end.