Check Daily, Water As Needed
Summer Planting in the Sacramento Valley
From the Davis Enterprise, June 28, 2007
Click here for summer transplanting guide
Simple answers don't begin with 'that depends.'
When people ask me how they should water their newly
transplanted trees and shrubs in the summer, my answer is often not simple. It
begins with 'what are you watering with?' Then we may need to discuss what type
of soil they have, what kinds of plants, and so on. But gardening is full of
rules of thumb, guidelines that are easy to remember. After all, gardening is a
mix of science, skill, and art. So let's come up with a simple answer to the
question: how should I water new plants during the summer?
Let's get one myth out of the way first: 'It's too hot to
plant here during the summer.' Nonsense!
Landscape contractors don't stop working in the summer.
Ideal temperatures for plants to establish and grow are 55 – 90 degrees
(F), which is the majority of our summer temperature range. A plant that can
grow in our climate can sustain short periods of very hot weather, even shortly
There are advantages and disadvantages to every season
here. Some advantages of summer planting?
Plants root quickly into warm soil, establishing faster
than in winter or spring.
You have greater control over soil moisture, so you can
dig a proper planting hole. Water thoroughly a couple of days beforehand, and
the soil will be perfectly workable.
Many plants prefer warm weather: subtropicals and
plants from Mediterranean climates, for example. Citrus trees planted in late
winter often sulk, whereas those planted in summer begin immediate growth.
Availability and quality from wholesale growers are
often better in summer. Propagation and production cycles of many plants have
them retail-ready in summer: shade trees, subtropicals, and Crape myrtles are
The key to success, regardless of season, is proper planting
Most important is how you water. Our margin of error about
watering is narrower in the summer. Plants should not be stressed to the point
of wilt, while watering too often leads to crown- and root-attacking fungus.
Therein lies the reputation that summer planting is difficult.
Aftercare includes the period of transplant stress and
early root establishment.
When you take the plant out of the pot, you will find
roots circling or bound up. Sometimes you have a solid cylinder of packed
roots. Pull, tease, or even cut
those roots to get them un-bound. Obviously that stresses the plant a bit.
Exposing the fine root hairs to the air kills them, and those are the
water-uptake part of the root. So the plant droops, even with adequate soil moisture.
But that period of shock only
lasts a few days: the fine root hairs re-grow immediately if the soil is loose,
warm, and moist.
After the first couple of days, the roots quickly begin to
grow out into the surrounding soil – especially if you have loosened it
at the time of planting. This is why we recommend digging a hole at least twice
as wide as the container, turning and crumbling and mixing the soil thoroughly.
Full root penetration into the surrounding soil occurs within about six weeks,
so that is how long it needs special watering attention.
So here is the first rule of thumb: check the plants
daily, water as needed.
Simple enough. But what does 'as needed' mean?
You could wait until the plant starts to wilt slightly,
poke your finger into the soil an inch or so, wait until it feels nearly dry to
Or you can calculate it.
Ok, so I actually have a degree in plant science. I should
be able to calculate how much water a plant needs. The evapotranspiraton rate
(ET rate) is a measure of how much water a plant uses, measured in inches
(gallons per square foot). All you need to know is the plant's canopy (leaf
area), look online at the weather data for Davis at ipm.ucdavis.edu, and you
can calculate how much water a plant used. Let's see: 1 inch of water = 0.62
gallons per square foot. The ET rate on June 21 was .27 inches at the Davis weather
station, so a 2-foot diameter plant used about one-half gallon of water (you still
with me?) that day.
Now, I haven't accounted for the variation in ET rates by
microclimate, because I have no way to measure ET on my own property. And plant
species vary in their actual usage: the ET rate measurements are based on turf.
So I'd need the landscape coefficients for my particular species to multiply (stop
yawning!) the ET figures, but that would, if anything, make the actual use rate
a bit lower. I'd have to do separate calculations for each plant based on size
and type, or figure out the average for the whole planting area.
I'm guessing most people won't find this approach very
All right, let's try a more hands-on technique. At the
nursery we water nearly every plant nearly every day during the summer. How
much water does it take to get the nursery soil thoroughly wet? I tell my staff
to count to five slowly for a #5 can, and to ten for a #15 can. The new plant
in the ground is still mostly in the nursery soil for the first couple of
How much water does your hose put out? At full throttle
about 7.5 gallons per minute in our area (contact your local water district to get information for your area, or calculate it from charts based on your water pressure and meter size). So here's how much we're watering each day:
4" pot: one quart
#1 can: 0.5 gallon
#5 can: 0.75 gallon
#15 can: 1 gallon
But there are a couple of issues with this approach once
the plants are in the ground.
watering in heavy soil encourages fungus that may kill the plant, especially in
hot weather. It's better to allow the soil surface to dry slightly between
So here's our second rule of thumb: Water every
other day, the following amounts:
* 4" pot: 0.5 gallon
* #1 can: 1 gallon
* #5 can: 1.5 gallons
* #15 can: 2 gallons.
You can do this with a hose or with a drip system. Most
drip emitters put out 1 – 2 gallons per hour, so you'll need to run the
drip line for 1 – 2 hours every other day.
My friend and associate, Deborah Flower, is a horticulture
instructor at Sierra College in Rocklin. When she was a graduate student at UC
Davis, she field-tested (literally) this approach with #1 and #5 size shrubs
planted in a field near Old Davis Rd. She made a simple berm of soil around the
nursery soil and watered the measured amounts by hand. She notes, 'when I used
this system I did not lose a single plant!'
2. The soil
around the nursery soil also needs to get wet, or the roots won't grow outward.
So use a sprinkler or your existing system to water the surrounding soil
thoroughly once a week. Set out some tuna cans to make sure you're applying 1.5
– 2 inches of water a week.
In her experiment, Debbie accomplished this extra
watering by thoroughly soaking the soil in a larger area around each plant.
Why not just use your sprinkler system for the new
plants? Because the other plants in your yard don't need water that often. It
is better to water the new plants individually. A simple drip watering system,
or a soaker hose, is best for the new plants if you can't hand-water. Be sure
that the drip emitter is positioned just over the nursery soil.
continues, 'they must be cautioned to not continue this frequency of watering
once the plant is established!' So here's our third rule of thumb: keep it up
for six weeks: that is, continue the
individual every-other-day watering, by hand or with a drip line, for six
weeks. A simple battery-operated timer can automate the process if you want to
go on vacation. It's ok to give new plants an extra drink on a windy day.
After six weeks, you should be able to set your timer to a frequency and depth of irrigation appropriate to the types of plants you installed.
A healthy plant, properly planted and watered, will
begin new growth immediately and you will gain a whole summer's growth!
Note: Deborah Flower's experiment and recommendations
are described in Pests of Landscape Trees and Shrubs, 2nd
Edition, Publication 3359 of the UC
Integrated Pest Management Program and available online at ipm.ucdavis.edu.
© 2008 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
Feel free to copy and distribute this article with attribution to this author.
Click here for Don's other Davis Enterprise articles