About the SFMGA

Saturday, January 26, 2008

How often should new plants be watered?

Ask yourself the following questions to develop a feel for watering frequency.

  1. How long since transplanting? Newly planted plants require more frequent watering than established plants. Begin to cut back the frequency after 2 to 3 weeks as the plant roots start growing out into the surrounding soil and the above ground portion of the plant shows strong signs of new growth.
  2. How hot and windy is it? Heat and wind cause increased water loss by plants. When daytime temperatures move into the 80’s, water newly transplanted plants every other day. Once the air temperature hits the 90 degree mark check the plants morning and evening, looking for wilted leaves as an indicator of dryness. Initially, a daily watering WILL be needed for small plants.
  3. How deep did that last rain penetrate the soil? Rain amounts can be deceiving. Always stick a shovel into the ground after a rain and do a visual check as to how deeply the water soaked into the soil. The soil needs to be damp at least 4 inches deep to do new transplants any good.
  4. What pot size was the plant was grown in? Small perennials and bedding plants transplanted from 4 packs and 4” pots will need more frequent irrigation than 5 gallon sized trees. Don’t water 4” and 5 gallon plants on the same schedule.
  5. Have the plants been mulched? Mulching plants can cut watering frequency by half (e.g. every other day vs. daily, twice weekly vs. every other day.)
  6. What type of soil you have? Compost enriched soils hold more water in the root zone that unprepared soils. Clay and loam type soils hold more water than sandy soils. Sandy soils dry out very quickly and plants will need very frequent irrigation when first planted. Also keep in mind that when climate conditions are very dry, extra water is needed to replaced moisture lost to the dry soil surrounding the planting hole.

To minimize the frequency of watering, mulch thoroughly, enrich the soil with compost and mix in water holding crystals (Broadleaf P-4). As a point of reference, during hot, rainless periods a healthy, established annual or perennial plant should be watered one to three times a week. A woody tree or shrub under these same conditions would need a thorough soaking once or twice weekly.

How much should the plants be watered?

Always construct an ample water saucer (well) around each plant and mulch. When it is time to water, fill the well twice allowing the water to be absorbed completely before filling it a second time. During the dry, hot months of the summer conventional turf lawns and groundcover beds will need one inch of water every week. Native grass lawns and xeric groundcovers need one inch every other week. Set out a rain gauge or coffee can to measure the amount applied.

When you water, soak the soil thoroughly. It is preferable to water more heavily and less frequently than to water lightly with much greater frequency. Deep watering promotes deep root growth.

What are signs of over-watering?

When the soil stays wet and the leaves of recent transplants become yellow and chlorotic looking, cut back your watering by half. Not half the amount, half the frequency. If you’re watering every other day, cut back to once every forth day.

If you are watering regularly but the leaves look wilted all the time, the plant roots are dying of suffocation. Too much water keeps the soil waterlogged and oxygen deficient. Pull back the mulch from the plant and let the top inch of the soil dry between waterings.

But these plants are supposed to be xeric!

“I planted my xeric Penstemon and watered it that day. I came back two weeks later and it was dead! I thought this plant didn’t need any extra water?” To this I say “yes and no”. No, xeric plants don’t need much extra water once established. But yes, even xeric plants need careful attention to their watering needs during the first growing season. Xeric plants have extensive root systems that pull water from the surrounding soil, but until a new transplant can re-establish its root system, it needs regular irrigation during rainless periods to grow and prosper.

Forget the Thumb over the end of the hose Method

When hand-watering with a hose, it is of critical importance that some type of water breaker be used. A hard stream of water straight from the end of the hose will dig-up smaller plants and expose the roots of trees and shrubs. We use a water wand (a tubular metal extension handle with a hand grip and thumb operated on-off valve) with a round waterbreaker on the end. The waterbreaker divides the forceful stream of water into hundreds of small streams thus dissipating the force of the water and creating a gentle rain to water with. Dramm makes an excellent water wand and waterbreaker combination.

When watering small seedlings or plants on a slope, I like to use a rose flare type waterbreaker to provide a gentle, low volume water flow. When hand watering on a slope with a rose flare, water until the water is not being absorbed by the soil and begins to run-off. Stop, let it soak in a few minutes and start again. Repeat this process 4 or 5 time until the soil is wet to a depth of 4 or more inches. This technique will reduce the amount of run-off and slope erosion.

And a Rule of Thumb

Watering schedules depend on where you live, the type of garden soil, the type of plants. Generally, non-xeric plants need irrigating 1 to 2 times weekly in the summer. Xeric plants need a deep soaking once every week to ten days. Very xeric trees and shrubs need a deep soaking monthly if conditions are dry.

Amount

  • A 5-gallon potted xeric shrub/tree needs 5 gallons of water per application
  • Most perennials need 1 to 2 gallons of water 2 times a week.