How to Make a DIY Self-Watering Planter (18-Gallon Tote System for Tomatoes & Vegetables)

Build a DIY self-watering planter using an 18-gallon tote. Grow healthier tomatoes and vegetables with step-by-step instructions, spacing tips, and troubleshooting advice.

Self-watering planters are one of the easiest ways to grow healthy vegetables in containers, especially tomatoes.

Instead of watering from the top and hoping moisture reaches the roots, this system stores water in a reservoir beneath the soil. The plants draw up moisture as needed through a wicking chamber, providing consistent hydration without daily guesswork.

I built my first 18-gallon DIY self-watering planters back in 2009, and I’m still using those same containers today.

Because I struggle with early blight in my garden soil, growing tomatoes in self-watering containers has made a dramatic difference. The foliage stays dry, soil doesn’t splash onto the leaves, and the plants remain productive all season. Celery, peppers, eggplant, cucumbers, melons, and summer squash also thrive in this system.

Many versions of self watering containers are sold online. For example, this self-watering planter is almost the same size as an 18 gallon tote. But, if you’ve ever wondered how to make a self-watering planter using inexpensive materials, this step-by-step tutorial will walk you through the entire build.

What Is a Self-Watering Planter?

A self-watering planter is a container gardening system that provides moisture to plants from below instead of from the surface.

Rather than watering the soil from the top, water is stored in a separate reservoir at the bottom of the planter. The soil above sits on an aeration shelf, and a small wicking chamber extends down into the water. As the soil dries, moisture is drawn upward through the wicking chamber, delivering consistent hydration directly to the plant roots.

This type of system is sometimes called a sub-irrigated planter (SIP), self-watering grow box, sub-irrigation system, or self-watering pot. But don’t worry, there is no electricity or pumps involved; it works naturally through capillary action.

Because the soil surface stays relatively dry, there is less evaporation, fewer weeds, and reduced risk of soil-borne diseases splashing onto plant leaves.

Benefits of DIY Self-Watering Planters

Self-watering planters aren’t just convenient; they create a more stable growing environment for your vegetables. When moisture levels remain consistent, plants experience less stress and grow more vigorously.

Here’s why this system works so well:

Consistent Moisture for Healthier Plants

One of the biggest challenges in container gardening is maintaining even moisture. Traditional pots can swing between soaking wet and bone dry in a matter of hours during hot weather.

Because water is stored in a reservoir beneath the soil, plants draw up moisture as needed. This steady hydration reduces stress and encourages deeper, stronger root systems.

Ideal for Tomatoes and Heavy Feeders

Tomatoes are particularly sensitive to inconsistent watering. Fluctuating moisture levels can contribute to problems like blossom end rot, cracked fruit, and reduced production.

Self-watering tomato planters help maintain steady soil moisture, which supports strong growth and more reliable harvests. Other heavy feeders like peppers, eggplant, celery, cucumbers, and melons also perform exceptionally well in this system.

Reduced Watering in Hot Weather

During the peak of summer, containers may need daily watering, sometimes twice a day. With a self-watering system, the reservoir holds a supply of water that can sustain plants longer between refills.

In hot weather, you may still need to top off the reservoir daily, but the process is simple and efficient: fill through the tube until water flows from the overflow hole.

Less Nutrient Loss

Because water is delivered from below rather than poured through the soil from above, nutrients are less likely to wash away. The enclosed system helps keep fertilizer where the roots can access it.

This makes the fertilizer strip method especially effective in self-watering containers.

Fewer Weeds and Cleaner Foliage

The plastic mulch layer covering the soil surface blocks light from reaching weed seeds. As a result, very few weeds germinate.

Additionally, because you aren’t watering from above, soil doesn’t splash onto leaves, an important factor in reducing soil-borne disease issues like early blight.

Why Self-Watering Planters Work So Well for Tomatoes

Tomatoes thrive when their growing conditions remain steady, especially soil moisture.

In a traditional container, the soil can dry out quickly on hot days. Then, when you water heavily, the roots are suddenly saturated. That cycle of drought and drenching stresses the plant and can lead to problems such as blossom end rot, cracked fruit, and reduced yields.

A self-watering tomato planter helps prevent those swings.

Because water is supplied from below through the reservoir, the soil remains consistently moist without becoming waterlogged. The roots grow downward toward the moisture source, creating a stronger root system and a more resilient plant.

For me, the biggest advantage has been disease management.

I deal with early blight in my garden soil. When tomatoes are grown in traditional beds, soil can splash onto the lower leaves during rain or watering. In a self-watering container, the soil surface stays relatively dry and covered with mulch. There is no overhead watering and very little splash-back, which helps reduce the spread of soil-borne disease.

Over the years, I’ve found that growing tomatoes in DIY self-watering planters results in:

• Healthier foliage.
• Fewer moisture-related problems.
• More consistent fruit production.
• A longer harvest window.

If you struggle with disease pressure in your garden soil or simply want a more controlled growing environment, self-watering containers can make a noticeable difference.

Other Vegetables That Grow Well in Self-Watering Containers

While tomatoes are the crop I grow most often in these containers, they aren’t the only vegetables that benefit from this system. Over the years, I’ve experimented with other moisture-loving crops and found that several perform even better in a self-watering planter than they do in traditional garden beds.

Celery

Celery was actually the crop that convinced me this system truly works.

Because celery has a shallow root system and demands constant moisture, I struggled to grow it successfully in traditional garden beds. Even with mulch and frequent watering, the plants became stressed, and the stalks were often tough and stringy.

Once I began growing celery in self-watering containers, the difference was dramatic. The consistent moisture from the reservoir kept the soil evenly hydrated, producing thicker, more tender stalks with far less effort.

If you’ve struggled with celery before, growing it in a self-watering planter may make all the difference. For a complete step-by-step guide to growing celery, see my detailed celery growing guide.

Other Crops That Thrive

In addition to tomatoes and celery, I’ve successfully grown:

• Peppers
• Eggplant
• Cucumbers
• Melons
• Summer squash

Any crop that benefits from consistent moisture performs well in this system.

How to Make a DIY Self-Watering Planter (18-Gallon Tote System)

Building a self-watering planter may look complicated at first glance, but once you understand the components, it’s a straightforward project. Most materials are inexpensive and easy to find at big box stores or online.

This system uses a water reservoir beneath the soil and a wicking chamber to supply steady moisture to plant roots.

Step 1: Gather Your Materials and Tools

Before you begin, collect the following items, then continue with the building instructions below:

Container Components

• A sturdy 18-gallon tote with a lid (approximately 24″ L x 16″ W x 16″ D)
• 3–4 inch wide and deep plastic container for the wicking basket
• 2 plastic coffee cans, or sturdy containers to support the aeration shelf
• A 24-inch pipe for the fill tube, about 1½ inch diameter, one end cut at an angle
• Landscape fabric
• Black plastic garbage bag (for mulch layer)
• Zip ties

Soil & Fertilizer

• 2 cubic feet high-quality potting mix (about 50–55 quarts)
• Organic granular fertilizer

Tools

• Drill with assorted drill bits
• Heavy scissors or jigsaw to cut the cover
• Saw for cutting the pipe
• Marking pen

Notes About Choosing Materials

A few material choices will make the difference between a planter that lasts one season and one that lasts for years.

Storage Totes

Choose a flexible, heavy-duty tote rather than a thin, brittle storage bin. I’ve learned over the years that inexpensive, rigid totes can crack after repeated drilling, sun exposure, or normal wear and tear. Spending a little more on a sturdy container will extend the life of your self-watering planter.

The Rubbermaid Roughneck and the Sterilite Ultra totes are more flexible and hold up to manipulation without cracking. I found these lovely blue ones on clearance for $5 and these are still being used years later.

Aeration Shelf Supports

The same principle applies to the supports that hold up the aeration shelf. In my first version, I used a lightweight plastic basket (shown in some of the photos). While it worked initially, it eventually flexed under the weight of wet potting mix and collapsed.

I switched to using recycled 30 oz. ground coffee containers, cut in half, for stable support that can handle the weight of moist soil. Whatever support you choose must be sturdy enough to hold the weight of damp soil.

The space below the aeration shelf becomes the water reservoir. Aim for a reservoir depth of 3 to 4 inches so it can hold a sufficient water supply. A deeper reservoir means fewer refills during hot weather.

Wicking Container

The wicking container is what allows water to move from the reservoir into the soil above. It is filled with damp soil and stays in the water. It does not need to be large or strong. I have used 3 to 4 inch tall aquatic plant basket, recycled yogurt containers and plastic food storage containers.

Potting Mix

Self-watering planters rely on capillary action to pull moisture upward from the reservoir, so the type of potting mix you choose matters. Heavy soil can compact and prevent proper wicking, and moisture control additives hold too much water.

Use a lightweight, well-draining container mix. I have used both Premier Pro-Mix BX and Miracle-Gro Potting Mix (without moisture control) with good results. I have also included a good DIY mix recipe below if you would like to mix your own from bulk ingredients.

Step 2: Build the Aeration Shelf

The aeration shelf separates the soil from the water reservoir and supports the growing chamber above.

Remove the Center of the Lid

Start by removing the center portion of the tote lid. A jigsaw works best for this step, but heavy-duty scissors can work on thinner lids.

Carefully cut out the middle, leaving about a 2-inch border around the edge. This outer rim will later help secure the plastic mulch layer to the top of the container, while the cut-out piece becomes your aeration shelf.

Cut an Opening for the Wicking Basket

Place your wicking container in the center of the aeration shelf and trace around it with a marker. Cut the opening slightly smaller (about 1/4 inch inside the traced line) so the basket fits tightly.

Drill Holes in the Aeration Shelf 

Before you attach the wicking basket to the aeration shelf, drill 1/4-inch holes spaced about 1 inch apart across the entire shelf to allow air circulation and moisture movement.

Drill multiple holes in the bottom and sides of the wicking basket to allow water to flow freely through it. Then attach the wicking basket to the aeration shelf and secure it with zip ties.

Attach the Shelf Supports

Cut the coffee containers in half, drill holes to allow water to flow, and zip tie the shelf supports to the aeration shelf. Make sure the supports are evenly spaced so the shelf remains level and does not bow in the center.

Step 3: Install the Shelf Assembly Into the Tote

Now that your wicking basket and supports are attached, flip the aeration shelf over, and place it inside the tote to check the fit.

Test the Fit

Press gently on the center of the shelf to ensure it feels stable before continuing.

Check that:

• The shelf sits level.
• There is space below for the water reservoir.
• Nothing shifts or collapses.

The shelf should fit snugly inside the tote without bending or buckling. Trim slightly if needed so it rests evenly inside the container.

Drill the Overfill Hole

Drill a 1/4-inch hole approximately 1/2 inch below the bottom of the aeration shelf. Water will come out of the overfill hole when the container is full. The hole also allows air circulation between the aeration shelf and the water.

Install the Fill Tube

Position the fill tube pipe vertically inside one corner of the tote. Trace around the pipe on the aeration shelf and cut a hole large enough for the pipe to pass through. Insert the pipe so it reaches the bottom of the container. The angled end should rest flat against the bottom of the tote to allow water to flow easily into the reservoir.

Step 4: Add Landscape Fabric

Cut a piece of landscape fabric large enough to cover the entire aeration shelf, leaving about a 2-inch overlap around the edges.

Cut openings in the fabric for the wicking basket and the fill tube. Lay the fabric flat over the shelf, and smooth it out so there are no large folds or gaps.

This layer prevents potting mix from falling down into the water reservoir while still allowing moisture and air.

Step 5: Move the Self-Watering Container to its Final Location 

Once filled, the planter can weigh over 100 pounds. Place your self-watering container in its permanent location. Be sure the fill tube is easily reachable to fill with a hose.

Step 6: Prepare and Add the Potting Mix

Self-watering containers only work properly if the potting mix is pre-moistened. Dry potting mix will not wick water effectively.

Add Wet Soil to Wicking Basket

Before filling the container, mix a small amount of potting soil with water until it is saturated. The soil should feel like a wrung-out sponge, evenly moist but not dripping.

Pack the damp potting mix firmly into the wicking basket. This ensures strong contact between the soil and the water reservoir.

Fill the Container in Layers

Add the remaining potting mix to the container, 3 inches at a time, saturating each layer with water until the container is full. This is important, as dry potting mix will not wick water. Continue until the container is filled to the top.

Step 7: Add the Fertilizer Strip

Instead of mixing fertilizer throughout the entire container, create a concentrated fertilizer strip at the top of the planter.

Dig a shallow trench across the center of the container, about 2 inches deep.

Add approximately 2 cups of organic granular fertilizer into the trench, then cover it with potting mix. I typically use an organic granular fertilizer such as Espoma Plant-tone or Tomato-tone.

Do not mix the fertilizer throughout the soil. Keeping it in a strip allows nutrients to dissolve gradually as roots grow toward it.

Water lightly from the top to activate the fertilizer.

Step 8: Install the Plastic Mulch

Lay the plastic garbage bag over the filled tote, cut a hole for the fill tube, and snap on the cover. The garbage bag will serve as plastic mulch, helping retain moisture.

Step 9: Plant Your Vegetables

Avoiding the fertilizer strip, cut holes in the mulch and add your transplants. Plant in opposite corners for larger crops like tomatoes, to allow adequate airflow.

For example, I plant two determinate or bush tomato plants in each 18-gallon self-watering container. I cut an X into the solar mulch at the opposite corners of the container, transplant the tomatoes, and add tomato cages. I added wood mulch on top, but this isn’t necessary.

Step 10: Fill the Reservoir and Maintain

Pour water into the fill tube until it begins flowing out of the overfill hole. This indicates the reservoir is full.

During hot summer weather, check the reservoir daily. Keeping it filled ensures the wicking system continues working properly.

How Many Plants Fit in an 18-Gallon Self-Watering Planter?

The number of plants you can grow in one 18-gallon self-watering container depends on the crop and its mature size.

For a tote measuring approximately 24 inches long x 16 inches wide x 16 inches deep, I recommend:

• 2 Plants: Tomatoes, Eggplants, and Summer Squash
• 4 Plants: Celery, Peppers, Cucumbers.
• 6 Plants: Broccoli, Cabbage, Cauliflower, Kale, Swiss Chard.
• 8 Plants: Lettuce, Spinach, and other Salad Greens
• 10 Plants: Beans, Beets, Carrots, Onions, Peas, Spinach, Turnip, Radishes

Use the spacing recommendations on your seed packet as a guideline, and avoid planting directly over the fertilizer strip.

Crops such as tomatoes, cucumbers, peas, and pole beans will require trellising or staking for support.

Best Potting Mix for Self-Watering Containers

Choosing the right soil mix is essential for a self-watering planter to function properly.

Unlike traditional containers, this system relies on capillary action to draw moisture upward from the reservoir. If the mix is too dense, compacted, or heavy, water will not wick properly.

Avoid using garden soil. It compacts easily, restricts airflow, and can block wicking. Instead, use a lightweight, well-draining container potting mix.

You can purchase a high-quality organic potting mix, or mix your own using:

• 45% peat moss or coco coir
• 45% finished compost
• 10% perlite
• 2 cups dolomite lime per 2 cubic feet (if using peat moss)

The finished texture should feel loose, fluffy, and slightly moist, never heavy or muddy.

Pre-moistening the mix before filling the container is critical. Dry mix will not wick water properly and can create dry pockets in the growing chamber.

How to Maintain a Self-Watering Planter

Once built, self-watering planters are simple to maintain.

Check the Reservoir Regularly

During cool weather, you may only need to refill every few days. In peak summer heat, check daily. Heavy fruiting tomato plants can use water quickly. Always refill through the fill tube until water exits the overflow hole.

If the potting mix dries out completely, the wicking action may temporarily stop working. Dry soil does not readily pull moisture upward from the reservoir.

If this happens, slowly water from the top until the soil is evenly moist again. Once the mix is rehydrated, refill the reservoir, and the system should resume working properly.

To prevent this issue, check the reservoir regularly during hot weather and refill before it runs completely dry.

Support Heavy Crops Early

Install tomato cages or stakes at planting time to avoid damaging roots later. Prune lower branches as needed to improve air flow.

Mid-Season Care

If plants begin to look pale or slow down mid-season, you can supplement with diluted liquid fertilizer poured into the reservoir.

End-of-Season Care

At the end of the growing season:

• Remove plants and old fertilizer strip.
• Loosen the soil.
• Refill the reservoir and flush if needed.
• Add a new fertilizer strip before replanting.

I’ve reused the same totes for years by simply draining them and storing them in a shed over winter.

Frequently Asked Questions About DIY Self-Watering Planters

Over the years, I’ve received many questions about building and using these self-watering planters. After growing in this system since 2009 and reading more than a hundred reader comments, a few common themes keep coming up.

Here are answers to the most frequently asked questions to help you troubleshoot and get the best results from your self-watering container. If you don’t find your answer here, please drop your question in the comments.

Is it safe to grow vegetables in plastic storage totes?

Most storage totes are made from food-safe polypropylene (#5 plastic), which is considered stable for gardening use. Avoid using brittle or unknown plastics, and choose sturdy containers from reputable brands.

If you prefer to avoid plastic altogether, the same self-watering design can be adapted to other container types, though plastic totes remain the most affordable and accessible option.

How deep should the water reservoir be?

The reservoir space beneath the aeration shelf should be at least 3–4 inches deep. This provides enough stored water to sustain plants between refills, especially during hot weather.

What happens if the soil dries out completely?

If the potting mix dries out fully, the wicking action may temporarily stop working because dry soil does not easily pull moisture upward from the reservoir.

To fix this, slowly water from the top until the soil is evenly moist again, then refill the reservoir. Once rehydrated, the system should resume working normally.

Do plastic totes crack over time?

Lower-quality or brittle plastic totes can crack after prolonged exposure to the sun or freezing winter conditions. I’ve had some inexpensive bins split over the years and needed to replace them.

Choosing a flexible, heavy-duty tote and draining it before winter storage can greatly extend its lifespan. My sturdier containers have lasted many seasons.

Can I make a self-watering planter from a 5-gallon bucket?

Yes. The same basic design can be adapted to smaller containers such as 5-gallon buckets. However, an 18-gallon tote provides more root space and a larger water reservoir, which is especially beneficial for tomatoes.

How often do you refill a self-watering tomato planter?

In mild weather, every few days may be sufficient. During hot summer conditions, you may need to refill daily. Always check the reservoir and refill when it is empty to maintain proper wicking.

Do self-watering planters prevent blight?

They do not eliminate disease entirely, but they help reduce soil splash and keep foliage dry, which can slow the spread of soil-borne diseases like early blight.

Can I reuse the potting mix next season?

Yes. Remove old plant roots, refresh the fertilizer strip, and top off with fresh compost if needed. Many gardeners reuse the mix for several seasons.

What vegetables grow best in self-watering planters?

Tomatoes, peppers, eggplant, celery, cucumbers, melons, and summer squash all perform very well because of their consistent moisture requirements.

Why I Still Use These Planters After All These Years

Over the years, I’ve tested different methods, grown vegetables in raised beds and traditional containers, and adjusted my approach as I’ve learned more. Yet I continue coming back to this simple system.

It gives me consistent results.

My tomatoes stay healthier despite early blight pressure in my garden soil. My celery grows with thick, tender stalks instead of turning stringy and stressed. During hot summer stretches, I’m not constantly dragging hoses around or worrying that my plants dried out while I was busy with other things.

What I appreciate most is the reliability. The steady moisture supply reduces plant stress, simplifies watering, and creates a more controlled growing environment, whether you’re gardening on a patio, driveway, balcony, or backyard.

This isn’t a trendy gardening trick. It’s a practical system that has proven itself season after season.

If you’ve struggled with inconsistent watering, disease pressure, or moisture-loving crops that never seem to thrive, building a DIY self-watering planter is well worth the effort. Once you make one, you may find yourself building several.

Good planning is key to a successful vegetable garden

Whether you are new to growing your own food or have been growing a vegetable garden for years, you will benefit from some planning each year. You will find everything you need to organize and plan your vegetable garden in my PDF eBook, Grow a Good Life Guide to Planning Your Vegetable Garden.