As a plant-loving overwater-er, I have been guilty of overwatering my beloved indoor plants - some of which are probably right at this moment cursing me out in Plant Heaven. But what could I do? I was a newbie gardener who had no clue even after sticking my finger into my plants’ soil several times. My love language was an excess of care, in this case, watering. So my less-hardy plants developed soggy leaves or browning leaves. Even the usually hardy Snake Plant stood no chance.

Fortunately, my Fiddle Fig Leaf community page staged an intervention and suggested a water meter. I gained valuable insight while my plants gained a literal life-altering experience at an affordable price.

Fast forward 2 years and I’m needing my water meters less. Still, I need the occasional help when I get a new plant or when the weather changes. I thought my water meter was all I needed until Ashley introduced me to the SUSTEE pen.

What is the SUSTEE Pen?

The SUSTEE is a slim pen-like watering meter. It’s a device that measures soil humidity and it lets you know if your plants need to be watered or not. The indicator is color-based so you can easily tell from a quick glance. This special aquameter solves the common problem of when to water and how much. Essentially, the SUSTEE pen makes a plant’s “thirst” visible.

Where can I buy Sustee Pens?

You can buy them online. Just click on the button below. When you get to the product page, just choose the sizes you need.

How do you use a SUSTEE pen?

The SUSTEE pen is very easy to use:

1. Stick the pen into the soil of your potted plant.

2. Monitor the indicator every day. White means the soil is dry and your plant needs watering. Blue means the soil has enough moisture and does NOT need watering.

3. Clean or wash the SUSTEE pen as needed.

Pro-tip: Always wait until the indicator is completely white before watering.

How do you use it for the first time?

1. For first time use, there are two ways you can go about it. Option 1: If you just recently watered, put your pen in a glass of water. When the indicator turns blue, transfer it to your plant pot. Option 2: Wait till your plant needs a full watering. When ready, stick the pen into the pot. Water and drain well till the pen is blue.

2. Place the pen within a 20cm radius from the plant so that it can monitor the soil around the roots.

3. Push the pen deep enough into the soil so that the ▼ or Ω mark is covered.

4. Waiting for the indicator to change color can take 3 to 30 minutes.

5. If the soil in your plant pot is packed, loosen it first with a trowel or other similar gardening implement so that you can insert the SUSTEE pen easily.

How much water do I use?

Water your plant until the window turns blue. You can also try using a fifth to a quarter of the volume of your pot. Water evenly and make sure the excess water drains out of the pot. Don’t let your plant sit on the excess water.

How is it different from other moisture meters?

You need 1 SUSTEE Pen per pot.

The most obvious difference of the SUSTEE pen versus regular moisture meters is that you need one pen for each potted plant.

If you are constrained by budget or have way too many plants, then that one-time purchase of a regular moisture meter might be more ideal for you.

The SUSTEE pen is less damaging to plant roots.

It is common to use the regular water meter with many plants. However, this means inserting the prongs of the device into the pot daily thereby potentially harming the roots of your plant on a regular basis. It was something I had to accept given no alternatives at the time and it actually kept me from checking soil humidity as often as I wanted.

This is solved with the SUSTEE pen because the device is fixed. With one pen dedicated to just one plant, I don’t have to poke my plants every time I want to take a water reading.

The SUSTEE pen minimizes disease infection between plants.

Another benefit to having dedicated pens versus one water meter for all plants is that it removes the possibility of diseased soil or plants infecting others especially in the case of fungus or mealybugs.

It’s not the perfect analogy but think of a nurse using one thermometer for many patients as opposed to each patient having their own thermometer.

The SUSTEE Pen takes out the guesswork.

With the regular water meter, the gauge has me dithering and uncertain sometimes since I either forgot or don’t know the correct watering level for each plant. Most water meters come with packaging that lists off the water level needed for the most common plants but it’s not a complete list obviously.

The SUSTEE pen takes out all that guesswork by simplifying the process. White means water right now. Blue means hold off.

Here’s a little story. I ordered this money plant and when it shipped, it was just a piece of wood with some roots. I had no idea how much water it needed but fortunately, I had the SUSTEE pen to guide me. I rejoiced when the first buds came out! I truly thought it was going to be a bust.

The SUSTEE Pen is made in Japan. Most water meters are made in China.

There are 3 countries that I watch out for when I look for country of origin for gadgets — Japan, Korea, and USA. I really like the quality of products made from these countries as they really last long and work very well. Again, if you’re on a budget though and just want to spend once, then get a generic water meter.

The above differences are actually what pushed me to adopt SUSTEE pens permanently in my indoor garden collection. No more poking each plant everyday and I do less guesswork with the simple white/blue indicator.

Can I use the SUSTEE Pen on any potted plant I have?

Yes, the SUSTEE Pen can be used on any potted plant. Each plant has a shared soil moisture range called “available water capacity”. SUSTEE technology is based on this range.

The SUSTEE Pen is effective for use in bog moss, Akadama soil, black earth, bark, coco peat, peat moss, vermiculite and other gardening culture soil. It can even be applied to hydroculture/hydroponics, bottom watering, container vegetable gardening, and roof-top open culture.

What size SUSTEE Pen should I use on my potted plant?

SUSTEE Aqua Meter pens are available in 3 Sizes:

1. Small Pen (12cm) is suitable for pot sizes Diameter 6-9 cm.

2. Medium Pen (18cm) is suitable for pot sizes Diameter 10.5-18 cm.

3. Large Pen (25.5cm) is suitable for pot sizes Diameter 18 - 65cm.

If you don’t want to break out the measuring tape, here’s another way to tell what size SUSTEE pen you need.

• Can you lift your pot with one hand? If yes, get the small pen.

• Do you need two hands to lift your pot? If yes, then get the medium pen.

• Do you need excessive force or extra help in lifting your pot? If the answer is yes, then get the large pen.

How long does it take the SUSTEE to change color?

The SUSTEE pen changes color in as little as 3 minutes and in as much as 30 minutes. Several factors affect the color change time and these include the type of soil you have, water retention level, and the amount of water you used. The below is only a guide but do remember that after the first use, the color change usually happens faster.

• Size S: Approximately 3 minutes

• Size M: Approximately 15 minutes

• Size L: Approximately 25 minutes

How do you clean the SUSTEE pen?

When too much soil has clogged the sensor, the pen might not react as swiftly as normal. Clean the pen by mixing mild detergent with warm water. Place the pen upside down with the indicator facing downwards. Soak for an hour until the debris comes off. Dry the SUSTEE till the window is white. It is now ready for use.

What is a SUSTEE pen core?

The SUSTEE pen core is a part of the device that needs frequent changing or refilling. Remember your refillable pens? The core is similar to the replacement cartridge.

These cores are very eco-friendly though. They are made of natural fibers and can be consumed by microorganisms.

How long does a SUSTEE pen last?

If you start using a SUSTEE pen, know that you will need to change the cores regularly depending on soil composition. The fastest that you’d need to replace the core refill is in about 6 to 9 months.

If your pen stops turning blue even after a thorough cleaning, take a peek at the bottom of the device. If the core refill has deteriorated and decomposed, it’s time to change it out.

Check out below what type of soil you have. This will help you know when you’d need to do a refill.

• Organic culture soil (for roses or home vegetable gardens): About 6 to 9 months

• Inorganic soil (for foliage plants etc.): About 9 to 12 months

• Hydroculture: About 1 to 2 years

• Bog moss/bark: About 1 to 2 years

• Peat moss: About 1 year

How do you change the SUSTEE pen core?

It’s very easy. Clean off your pen and twist the cap off. Remove the used core and replace with a new one. Make sure that you remove all the components of the core — the inner core, blue sheet, and the straw. Use a pair of tweezers if you’re having difficulty fishing out the parts.

I’m a visual learner so I made sure to look up videos and photos of how to change out the core. Check out the instructions below or better yet, watch the video at the bottom of this post. The 20 Questions video demonstrates how to change the cores at the 3:46 mark.

What do I do? My SUSTEE pen isn’t working.

Let’s troubleshoot!

First time usage

If it’s your first time to use your device, you may not have used enough water. Time your first-time use when your plant’s soil is dry. Insert the SUSTEE into the pot 20 cm from the plant. WATER THOROUGHLY. This means you’ll need to water until the excess is dripping onto your plant saucer.

The first time I used my SUSTEE, I was afraid to water this much so I watered sparingly. As you can guess, my pen didn’t turn blue that time and I had to research what I’d done wrong.

Another thing you need to remember is that you will need to wait. The indicator takes time to work the first time the pen is used. It gets faster after succeeding uses.

The SUSTEE is clogged

It’s easy to miss but the device has a hole at the bottom. It will eventually get clogged up with soil, growing roots, and other material so the pen may stop functioning properly. If this happens, just clean it as per the instructions above.

You can avoid getting your pen clogged though. Just make sure to loosen the soil before inserting your pen or trying a new spot to insert it.

Your soil is too well-draining

Most potting mixes for succulents and indoor plants are very much well-draining and porous. This means that during watering, the water may drain too quickly that the SUSTEE pen may not have enough time to do its measuring job. To help it along, pour water mindfully over the bottom of the pen when watering the plant.

Useful Videos To Watch

Here is an excellent introductory video that really helped me in the beginning. It shows you how it works and how to use it for the first time.

Another great video on SUSTEE is this video by Plants in a Box. They not only answer the most asked questions about the pens but they demonstrate them. It really makes a difference when somebody knowledgeable shows you exactly how it’s done. They demonstrate how to use the SUSTEE, how to clean it, and how to change out the cores.

About SUSTEE

Here’s a little bit of background information about the SUSTEE pen.

The SUSTEE pen was developed by product designer Tetsutaro Nakabayashi. It has been tested and researched in cooperation with Japanese farmers and the Tokyo University of Agriculture.

An award-winning invention, it has won multiple international awards including the Reddot Design Award, Germany Design for Asia Award, and the Japan Good Designs Award.

I’ve had my SUSTEE pens for months now and I can really feel the quality of these little buggers.

And about my lack of a green thumb, I feel vindicated. Japanese farmers say “it takes three years to learn watering plants properly.” In the meantime, I have my trusty water meter and my SUSTEE pens to help me along.