How to Water a Bonsai Tree

Monitoring Moisture Levels

Feel the top of the soil with your fingers to check dryness. Place 2 to 3 fingers at the base of the bonsai tree, just around where the trunk enters the soil. If it feels damp, there's no need to water it. Otherwise, it's too dry and is in need of water. If the soil on the sides of the planter feels dry but the soil near the trunk is damp, don’t water it and check it again in about 8 to 12 hours.

Inspect the top layer of soil for a grayish color. Bonsai soil is made from a mix of crushed substrates like lava rock, peat, and brick—it looks more like gravel than dirt. When it's time to water, this top layer will appear extra loose and dull-gray in color. Bonsai trees won't grow well in regular potting soil because the thick, rich soil holds too much water and may cause root rot.

Use a wooden chopstick as a moisture gauge. Hold the chopstick by the thicker end and insert the narrow end 1 inch (2.5 cm) into the soil. Pull it out to check the water line before every day or touch it to your inner wrist or cheek to feel for moisture. Reinsert the chopstick into the soil at least 3 inches (7.6 cm) away from the trunk of the tree so it’s ready to check the next day. Use a clean wooden or bamboo chopstick—this won’t work with ceramic or plastic chopsticks. Don't stick the chopstick into the soil any deeper than 1 in (2.5 cm) because doing so might disturb the root system. Some store-bought bonsai trees come with small wooden posts for this very reason.

Top-Watering a Bonsai Tree

Fill a rose-spout watering tin with 2 cups (470 mL) of water. A rose-spout has lots of tiny holes in it to ensure the water comes out gently so the pressure from the water doesn’t disturb the soil. It will also make watering easier because the rose-spout covers a wider area than a mono-spout. You can buy a rose-spout watering can or rose attachment at most garden supply stores. You can also attach a rose cap to a garden hose for outdoor bonsai trees. If it’s hot outside and your bonsai is outdoors, make sure to use room temperature water to avoid shocking the root system.

Pour water over the tree until you see puddles on the top of the soil. Gently pour water out of the rose spout onto the soil. Move the spout around to moisten the entire surface of the soil. Slowly watering the tree will give the water time to soak into the soil and slowly travel downwards. If you're using a rose attachment on a garden hose, point the cap upwards so the water travels in an arc and lands gently on the bonsai soil.

Don’t water the leaves if your bonsai is in full sun on a hot day. It’s generally okay to get the leaves wet. However, on hot days, any water droplets that get on the leaves can magnify the light rays and burn the leaves. If you live in an area that gets very hot during the day, avoid splashing the leaves with the water. As an alternative, keep the bonsai in a shaded area during the summer so you don’t have to worry about scorching the leaves.

Stop watering when you see puddles forming or water draining from the base. It should take about 30 seconds to fully saturate the soil. Water coming out of the drainage holes is a good indicator that the soil is nice and moist. The water coming out of the bottom of the planter should be clear, not brown or gray. If it's brown or gray, water it again in 15 to 20 minutes.

Wait 15 to 20 minutes before watering it again if necessary. If the top layer of soil feels dry already or if your bonsai needs a little extra love, pour another helping of water over the soil. The idea is to fully saturate the soil but not so much that it stays sopping wet, so stop watering as soon as you see water dripping out of the bottom. If you notice yellowing leaves or shriveling branches, skip the second watering because these are signs of oxygen deprivation due to too much water. If your bonsai tree has crispy leaves, do a third 30-second watering or revive it in a water bath.

Immersing a Small Bonsai Tree

Fill a large tub or container with 2 inches (5.1 cm) of water. Choose a tub that's big enough to fit the bonsai planter into it and deep enough to hold 2 inches (5.1 cm) of water. Make sure the container is clean before filling it with water. This is only necessary if your bonsai shows signs of dehydration like crispy, wilting leaves.

Place the bonsai upright into the center of the tub. Make sure the water doesn’t spill over the top sides of the planter. The idea is that the water will travel from the bottom to the top of the soil through the drainage holes. If the bonsai tree is in a light, plastic container, it may float at first. Press and hold it down until it stays in place.

Check the soil for dampness after 5 to 10 minutes. You'll know the soil at the top of the container is moist when it darkens in color. If you're not sure, feel it with your fingers. If it's adequately moist, the soil will feel wet and give a little under your finger. If the soil feels dry and doesn't leave a depression when you press it down, leave it in the water for another 5 minutes and then check it again.

Place the bonsai in the sink or on an outdoor table so it can drain. The water needs to drain out of the bonsai after the soak, so put it somewhere you don’t mind getting wet. An outdoor patio or bench is a good spot. You can also place the bonsai on a drainage tray if you keep the plant indoors. Just be sure to check on and, if necessary, empty the shallow tray after 15 to 20 minutes so water doesn't overflow.