You may wonder, if it rains so much in Olympia, is it really necessary to water the roses?

Unfortunately, yes.  Our summers are very dry, and our soil is charitably described as 'excessively well drained'.  That means the soil dries out fast after the winter rains stop.  Roses need about 1" of water a week, but we don't get anywhere near that much during the growing season - May through September.

Some roses can go unwatered.  Wild roses won't need watering.  Once-blooming roses won't need much water.  Very large, old, well-established roses can go a long time between waterings.  Roses that you don't care much about can go without watering.  But for most roses, if you want them to be healthy and to produce flowers, you'll have to water at least once a week in the summer.

Different soil types have different water holding abilities. Soil type refers to the particle sizes of soil, which determine the pore sizes, which determine the water holding capacity and drainage. Soil structure also affects water holding capacity. Structure means how the particles stick together - grains, crumbs, blocks and hardpans. Loose structure, called friable, like grains, crumbs and small blocks absorb water easily while larger blocks and hardpans might not absorb water at all, acting like rock or concrete and not like soil.

When you water your garden, you’re not watering your plants. What you’re actually doing is refilling the soil water. Soil isn’t just what you stick the roots into. Soil is a living thing that acts like a sponge or a reservoir, for water and nutrients for plants. When it rains, or when you water the garden, water fills the pore spaces in the soil. Once the pore spaces are full the extra water runs off or drains away. When it first starts raining in fall, the soil is very dry so most all the rain soaks in. Over winter the soil fills up with water, and normally by spring the soil is at full capacity and then some, ready for plants to start growing and pulling up water for their own use. As plants pull out more water and rainfall decreases, the soil slowly dries out until we have to start watering our roses, usually some time in May or June. Then we continue to water them until they slow down growth as temperatures cool in September.

There are three basic size categories of soil particles: sand, silt and clay. Of course here we have a fourth category, rocks and gravel but those aren’t technically soil. And organic matter is critical to soil health and water holding capacity but it’s not included as a soil particle. Most soils are a blend of all three particle sizes and the ratio determines the soil type: loam, sandy loam, silty clay, whatever. Particles leave spaces between them.  These are the soil pores. Sandy soils with large particles also have large pores. Clay soils with very small particles also have very small pores. Large pores drain fast and don’t hold water, but let lots of air into the soil. Small pores drain slower and hold water longer, but let in less air. Most soils average about 50% pore space, so that’s the volume that’s available for holding water and air.

Sandy and gravelly soils drain fast, absorb fast and don’t hold much water. They need to be watered more often but for less time as water absorbs fast and travels through the large pores quickly. Water also tends to travel straight down in sandy soils, not spread out. So if you’re watering with a drip or a hose, you need to make sure you water all around the plant or only the roots directly under the hose will get any water.

Clay soils drain slowly, absorb slowly and hold water well. They need to be watered less often, slower and for longer than sandy soils. Water takes longer to soak in, but once it’s in it stays in, and the small pores hold a lot of water a long time. Water spreads out in clay soils too so you don’t need drip emitters as close together as in sandy soils.

Loam soils are those with a balance of sand, silt and clay. They’re the best soils for gardening in because they balance drainage, infiltration and water/air holding capacity. Clay is necessary to hold water, and sand is necessary to allow in air.

So, in order to know how far apart to put emitters, and how often to water for how long, you need to know what kind of soil you have. Here’s how to find out.

The mason jar test - fill up a quart size mason jar half way with soil from the garden. You can remove sticks and leaves and larger rocks first. Then fill the jar with water to the top and shake it up so all the dirt is shaken around in the water. Set the jar down and grab a ruler. At one minute the sand has settled out - measure it and write it down. Allow 6 hours for the silt to settle out, measure and record. Allow 3 days for the clay to settle out, measure and record. What’s left floating is the organic matter, which doesn’t get measured even though you want lots of it. Now divide each measurement by the total inches of soil for the ratio of sand to silt to clay, and use the soil chart below to find out what you’ve got.

Let’s assume we’re working with sandy loam soil. It will drain and absorb pretty fast and the water won’t spread out far. WSU recommends watering shrubs like roses enough to saturate the top 12-18 inches of soil, then allowing the top few inches to dry.  Sandy soils will need 1 inch of irrigation or rain to soak that top 12 inches of soil, and loams will need 2".

How long to water? If you’re using a spray like a lawn sprinkler, do the tuna fish can test to find out how long it takes for your sprinkler to put out 1" of water.

If you’re using a drip system or a hose end, it’s easier to measure by gallons over time than by inches.  One inch of water roughly equals one half gallon per square foot of garden, according to the ARS website, and roses need about 5 gallons of water a week in summer. Your drip emitters will be rated by gallons per hour so that’s easy to calculate. Your hose end you will have to measure by timing how long it takes to fill a one gallon bucket. If you’re using a soaker hose you’ll have to guesstimate how open the faucet is when the soaker is running full blast, and see how long that takes to fill that one gallon bucket.

Your average hybrid tea rose takes up around 2 square feet of garden space, up to 4 sqft for large shrubs or climbers; so, a smallish hybrid tea in sandy loam soil will need about 1.5 gallons of water at a time, and about 5 gallons a week in warm dry weather (June, July and August). So, water 2 to 4 times a week, 1.5-2 gallons at a time, depending on temperatures.
In loamy soil add twice as much water at a time, half as often, to get the 5 gallon/week total. A larger rose will need more water, minis and polyanthas less.  And of course if it rains, you can deduct the amount of rain from the one inch needed by the roses.

Watering Methods

Roses can be watered by hand, by hose-end sprinkler, by drip system or soaker hose, or by fixed-spray lawn-type sprinklers.  Each has its advantages and disadvantages.

Watering by hand is the cheapest and simplest way to water your roses, and can be best when you have just a few plants.  You get an opportunity to spend some quality time with your roses when watering by hand.  But, it's boring - so boring that it's unlikely your roses will get enough water, as you'll give up and go away before they're done.

Hose-end sprinklers are the next cheapest and simplest.  Just attach the sprinkler to the hose, set it in the garden, adjust the location and the water pressure, and let it run.  Use a battery-powered faucet timer to shut the water off.  The disadvantage is it's not very precise, and foliage can block the water spray.  Watering the foliage can increase blackspot, but it also discourages mites.

Soaker hoses are very simple too.  Lay the hose out in the garden, attach the hose coming from the faucet, and let it run.  The disadvantage is that in sandy soils, the water doesn't travel very far at all from the soaker hose - just a few inches at most, so you need to just about cover the whole garden with hose going back and forth to get good water coverage.  The advantage is that you don't get the foliage wet, so less blackspot, and you don't water the sidewalk trying to cover the whole garden.

Drip systems take some time and some thought to lay out, but are wonderful once installed.  They're not terribly expensive either.  Drip components that spread water over a wide area are the best in sandy soils - laser tubing for instance, like a miniature soaker hose; or shrub bubblers that spray out small streams of water in a circle or semicircle.  Make a ring around each rose with the laser tubing, or use 3 or more bubblers or emitters around each bush.  You will want to buy all your parts from the same brand to avoid getting parts that should, but don't quite, fit together.  Also, compression fittings take some hand strength to put together.  If you have arthritis or tendonitis, look into fittings that twist together instead, like DripWorks' Easy Loc™ fittings.  Drip systems can be easily automated with either battery-operated faucet timers, or connected to a lawn sprinkler timer that runs off of household current.

If you have an underground irrigation system, most brands include shrub spray heads that will work well for watering roses.  Make sure your roses are on their own circuit however, not on the same circuit as the lawn.

DripWorks is a great source of drip irrigation expertise and supplies, highly recommended.  Their Easy Loc™ fittings are wonderful, and can be reused when you want to make changes to your drip system.  They also carry fertilizer injectors that work with irrigation systems.