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Rainwater Harvesting 101: Learn to Garden with Less Water with Martha Retallick, Ep 314

In a time where it feels like the weather is getting more and more volatile no matter where we live, making sure that you can capture rainwater is so important for so many people around the world. That's what this entire episode is about. And to help me with this topic is my plant friend Martha Retallick, author of Water Harvesting 101, who’s mastered the art of collecting and reusing rainwater after years of living through droughts in Tucson, Arizona. In our conversation, she shared how to redirect, collect, and reuse water for free! Let's start collecting, plant friends!

In this episode, we learn:

[04:21] Who is Martha Retallick?
[06:37] What is gardening in Tucson like?
[07:02] Why rainwater beats tap for plants
[09:01] What is water harvesting and its 3 pillars?
[11:00] What are the benefits of water harvesting?
[13:06] What are some drought-tolerant natives (mesquite, palo verde, ironwood)
[14:17] Redirecting rainwater 101
[14:29] Basins vs bowls
[15:43] Bring calm to every breeze with Wind River Chimes!
[17:22] Stay grounded all year with the American Horticultural Society Weekly Planner!
[19:13] Overflows & berms
[20:31] Flat yard? Start with basins
[22:37] Starter cisterns: rain barrels (daisy-chain, screens, overflow)
[25:07] Is stored rainwater potable?
[25:34] Stepping up to cisterns
[27:27] Planning placement and calculating your water budget
[29:53] Common mistakes with cisterns and irrigation
[30:36] Drought fallback: plant nitrogen-fixing beans
[32:34] Low-tech gauge to check water level
[33:19] What are the fall crops Martha likes to grow?
[34:56] What counts as gray water (and what never does)
[35:42] Two-way valve (redirect washer water to trees)
[37:06] What to look out for when harvesting water for your landscape
[38:01] The importance of “varying your flavors of water”
[38:40 Where to find Martha’s book and free cheat sheet!
[39:17] Reflections on water usage

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The Reality of Desert Gardening

In Tucson, using city water can be expensive, and it contains salt that plants don't love. So Martha started reusing water from daily life.

She uses Oasis brand soap, which is designed to be water-harvesting-friendly. Still, she learned that even eco-friendly soaps can build up salts, so she rotates her water sources: gray water, rainwater, and city water.

She highly recommends “varying your flavors of water.”

What Is Water Harvesting?

Martha defines water harvesting as three simple activities:

Redirecting rainwater – move it away from places you don’t want it (like flooding your house) to places you do want it (your garden).
Storing rainwater – keep rainwater for later in barrels or tanks.
Recycling used water – use what’s left from laundry, dishes, or showers to water plants.

She started doing this after her house flooded during a big storm. With help from a local nonprofit group, she reshaped her yard so that rain now flows into her garden instead of into her house.

Now, she captures the water instead of losing it and her plants are happy because of it.

Passive vs. Active Water Harvesting

Martha explained that water harvesting comes in two main forms:

1. Passive Systems

This means using the shape of your land to collect rain naturally. Martha uses:

Swales – rocky trenches that guide rainwater downhill
Basins – shallow dips in the soil where water can rest and soak in
Berms – small mounds of soil around her yard that keep rain from running into the street

These slow water down, give it time to soak in, and prevent flooding.

2. Active Systems

This means storing water for later use with rain barrels or cisterns.

Rain barrels are easy to start with: a 50-gallon container that catches roof water through your gutter. Just add a screen to keep out leaves and mosquitoes, and you’re in business.

From there, you can upgrade to a cistern. Martha says that she has a 1,500-gallon cistern in her yard that stores water for her raised beds and fig tree.

What If Your Yard Is Flat?

You can still harvest rainwater! Martha suggests digging a few small basins and connecting them with tiny channels. That way, the water moves slowly and doesn’t flood your home.

Her own yard can hold about 250 gallons of water during a heavy rain.

A Quick Guide to Rain Barrels and Cisterns

Rain barrels: simple, cheap, and great for beginners.
Always add an overflow outlet so extra water can drain safely.
Keep the barrel covered with a screen to stop bugs and leaves.
Don’t drink the water unless it’s filtered ( birds hang out on roofs, and, well… you don’t want to drink that.)
Cisterns can be above/below ground. Martha’s is above ground, and she uses a short hose and watering can to fill her garden beds.

If you’re wondering how big your cistern should be, check out Watershed Management Group’s Water Budget Calculator. These help you estimate your water use and storage needs.

Water Harvesting Mistakes to Avoid

Here are a few lessons Martha learned the hard way:

Don’t plant more than your water can handle.
Install your system before the rainy season so you can fill it up.
Be okay with losing a few plants.

When her garden struggled one summer, she planted tepary beans, an old desert crop that “thrives on neglect.” Not only did they survive, they fixed nitrogen in the soil and prepare it for the next planting season.

Gray Water 101

Not all water reuse is complicated. You can start today.

Put a bucket under your tub spout while the shower warms up. Then use that water for your plants.

That’s gray water: used water from showers, sinks, or laundry (but not from toilets).

If you want to make it automatic, you can ask a plumber to install a two-way valve that lets your washing machine water go outside to your garden. Just remember to use biodegradable soap with little or no salt.

The Beauty of Mindful Water Use

After years in the desert, Martha says she and her neighbors are the kind of people who turn off the tap while brushing their teeth.

When I visited Arizona, I felt that same shift in awareness. You notice water differently. You value it more.

And maybe we all should… even if we live in places with lots of rain.

Mentioned in our conversation:

Oasis Soap Bar
Water Budget Calculator | Watershed Management Group
Water Harvesting 101 Book by Martha Retallick
Growing Joy 275: Water Saving Techniques for Your Garden with Noelle Johnson

Thank you to our episode sponsors:

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Quarto: Weekly Planner by the American Horticultural Society

Whether you love a paper planner or know someone who can't live without theirs, the American Horticultural Society has the perfect plant lover planner for you! Filled with vintage botanical illustrations of North American native plants, each page contains blank weekly layouts so you can start whenever you want and track your appointments and to-dos more freely. This beautiful botanical planner is complete with a ribbon marker so you always know which page you're at.

Grab your Weekly Planner at quarto.com and wherever books are sold and fill your days with botanical beauty!

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