How to water a garden and how often is a question that gets asked all the time. I've been gardening for close to a decade now and this question stumped me this weekend. I bought a bunch of roses from David Austen last year and bought six different varieties of salvias as companion plants for them. Salvias give off sulphur which keeps roses disease and pest free. Or so I've read. Back to my watering issue. I'm growing both the roses and the salvias in pots. My roses are doing great but my salvias are not. I went from watering once a week to going to talk to my local nursery and finding out I was under-watering and changing my schedule to watering three times a week.
Much to my chagrin, the leaves on my salvias kept turning yellow and a bronze discoloration began to creep in from the edges of the leaves. Back I went to the nursery and talked to a master gardener and they said to go back to watering once a week and feeding the salvias more as the bronze color was a nutrient deficiency.
I'm now back on the once a week watering program but it got me thinking about how maddening setting a good water schedule can be. Drainage is super important in both containers and in your actual garden and most plants do not like sitting in water for long periods of time. But how often to water?
The answer is IT DEPENDS ON THE PLANT.
Rule #1: Water Deeply.
What does watering deeply even mean? The goal when you water deeply is to reach several inches past the length of your plants roots to hydrate the entire root system. But this means that you need to know what the length of your plant's root system is and what type of soil it's planted in.
In a container, ideally you want to water well enough that the water hits the bottom of the container. You can buy a 9" long water meter to make sure your soil is getting the moisture it needs. I find that if i fill the top of the container with an inch or two of water and let it soak in, repeat this about 3-4 times, I get the entire plant root system drenched. I live in Southern California where we don't get rain at all so I water once a week in the spring, two to three times a week in the summer, and back to once a week in the fall.
If you are watering an in-ground garden bed (definitely invest in irrigation, it's a life changer) but you do need to know what your soil is and its drainage.
- If you have sandy soil, the water will drain quickly away not properly hydrating the roots.
- If you have silty soil, water will first spread out and then drain away.
- If you have clay soil, water will spread out shallowly and then drain away very slowly.
So not only do you need to know your plant but also your soil and the rate it drains. You can run a percolation test to both see what your soil is and how its draining.
PERCOLATION RATE TEST
1.First, dig a small hole about 12 inches deep by 12 inches wide in an area you want to grow in. Try to keep the walls vertical.
2.Fill the hole with water and leave it overnight. (Keep the soil you dug up in a bag or bowl for use the next day.
3.The next morning, fill the water backup again and measure how much it’s draining every hour. The way I did this was to put a small stick across the hole as a level and then used a ruler or measuring tape to first measure from the top of the water to the bottom of the stick. I recorded that.
4. Come back an hour later and do the same measurement. From the bottom of the stick to the top of the water. Record your results.
The rate of drainage per hour is called the percolation rate.
Standard percolation rates of the types of soils:
1.Sandy soils have a range of 1-8” or more per hour.
2. Silty soils (this includes Loam) has a percolation rate of 0.1 to 1” per hour.
3. Clay soils of .1” or less an hour.
Once you have your percolation rate and the soil you are growing in, you can better access the time you need to fully water deeply. This takes us to the next step of good watering practices.
RULE #2: Water from the bottom, never overhead.
Your plant's roots need the water, not the leaves. Getting the leaves wet helps fungus and diseases grow. You definitely don't want that. Also if you use a wand, many times the water can't get past the leaf canopy of your plant to get to the soil.
This is when the magic of drip irrigation helps everything out. I started with a wand and it would take me a long time to water my very small garden. I wasn't happy and neither were my plants. When I set-up my drip irrigation my plants grew exponentially and I was able to better hold to my watering schedule. I have clay soil that I've amended with compost heavily to get it more towards that loamy perfection and I run my drip line for 30-45 minutes two times a week in the summer. The great thing is you can also set it on a timer so you don't even have to remember to turn it off and on,
Drip irrigation conserves water and gets the water exactly to where it needs to go, straight to the plants roots.
Rule #3: How often you water depends on your climate zone, soil and the plant you are growing.
I wish there was a better answer then this but since we all live in different climates and plant in different soils there is no blanket rule. Once you know the type of soil you have, you can ask your local nursery for guidelines for your climate. If you get a lot of rain in the summer, and are growing drought tolerant plants like salvias, you won't need to water them that often. With the heat of the Los Angeles summer, I sometimes have to water daily although having a 2" layer of mulch in my garden helps thing considerably.
