When watering the Costus tonkinensis, you should aim to use filtered water that is at room temperature. Filtered water is better for this plant, as tap water can contain particles that are harmful to its health. The reason that the water should be at room temperature or slightly warmer is that the Costus tonkinensis comes from a warm environment, and cold water can be somewhat of a shock to its system. Also, you should avoid overhead watering for this plant, as it can cause foliage complications. Instead, simply apply your filtered room temperature water to the soil until the soil is entirely soaked. Soaking the soil can be very beneficial for this plant as it moistens the roots and helps them continue to spread through the soil and collect the nutrients they need.

Both overwatering and underwatering will be detrimental to the health of your Costus tonkinensis, but overwatering is a far more common issue. When this species receives too much water, its stems and leaves may begin to wilt and turn from green to yellow. Overwatering over a prolonged period may also lead to diseases such as root rot, mold, and mildew, all of which can kill your plant. Underwatering is far less common for the Costus tonkinensis, as this plant has decent drought tolerance. However, underwatering remains a possibility, and when it occurs, you can expect to find that the leaves of your Costus tonkinensis have become brittle and brown. It is crucial that you notice the signs of overwatering as soon as possible when caring for your Costus tonkinensis. Some of the diseases that arise from overwatering, such as root rot, may not be correctable if you wait too long. If you see early signs of overwatering, you should reduce your watering schedule immediately. You may also want to assess the quality of soil in which your Costus tonkinensis grows. If you find that the soil drains very poorly, you should replace it immediately with a loose, well-draining potting mix. On the other hand, if you find signs that your Costus tonkinensis is receiving too little water, all you need to do is water more regularly until those signs have subsided.

If your plant is in a pot. The most precise way to decide whether your Costus tonkinensis needs water is to plunge your finger into the soil. If you notice that the first two to three inches of soil have become dry, it is time to add some water. If you grow your Costus tonkinensis outdoors in the ground, you can use a similar method to test the soil. Again, when you find that the first few inches of soil have dried out, it is time to add water. During the spring and early fall, this method will often lead you to water this plant about once every week. When extremely hot weather arrives, you may need to increase your watering frequency to about twice or more per week. With that said, mature, well-established the Costus tonkinensis can show an admirable ability to withstand drought.

When it comes time to water your Costus tonkinensis, you should not be shy about how much water you give. With the first two to three inches of soil dry, this plant will appreciate a long and thorough watering. Supply enough water to soak the soil entirely. The amount of water you add should be enough to cause excess water to flow through the drainage holes at the bottom of your pot. If you don’t see excess water draining from the pot, you have likely underwatered your plant. But do not let the water accumulate inside the soil, which will be very dangerous to the plant as well. Alternatively, a lack of water draining through the pot could indicate poorly draining soils, which is detrimental to the health of this plant and should be avoided. If the plant is outside, 1 inch of rain per week will be sufficient.

The water needs of the Costus tonkinensis can change depending on growth stages as well. For example, when your Costus tonkinensis is in the first few years of its life, or if you have just transplanted it to a new growing location, you will need to give more water than usual. During both of those stages, your Costus tonkinensis will put a lot of energy towards sprouting new roots that will then support future growth. For those roots to perform their best, they need a bit more moisture than they would at a more mature phase. After a few seasons, your Costus tonkinensis will need much less water. Another growth stage in which this plant may need more water is during the bloom period. Flower development can make use of a significant amount of moisture, which is why you might need to give your Costus tonkinensis more water at this time.

The Costus tonkinensis will have its highest water needs during the hottest months of the year. During the height of summer, you may need to give this plant water more than once per week, depending on how fast the soil dries out. The opposite is true during the winter. In winter, your plant will enter a dormant phase, in which it will need far less water than usual. In fact, you may not need to water this plant at all during the winter months. However, if you do water during winter, you should not do so more than about once per month. Watering too much at this time will make it more likely that your Costus tonkinensis will contract a disease.

It is most common to grow the Costus tonkinensis indoors for any gardener that does not live in temperate and tropical regions. Those gardeners should consider the fact that soil in a container can dry out a bit faster than ground soil. Also, the presence of drying elements such as air conditioning units can cause your Costus tonkinensis to need water on a more frequent basis as well. if you planted it outside. When that is the case, it’s likely you won’t need to water your Costus tonkinensis very much at all. If you receive rainfall on a regular basis, that may be enough to keep your plant alive. Alternatively, those who grow this plant inside will need to water it more often, as allowing rainwater to soak the soil will not be an option.

Costus tonkinensis requires about 3-6 hours of direct sunlight each day to thrive. However, it also needs some shade during the hottest parts of the day to prevent sun damage. Morning sunlight is ideal for Costus tonkinensis, but it can also tolerate some afternoon sun if the temperature is not too hot. To provide the perfect balance of sunlight, try planting Costus tonkinensis in an area that gets partial sun, such as under a tree or on the east side of a building.

If Costus tonkinensis is exposed to too much direct sunlight, its leaves may turn yellow, dry out, or even burn. You may also notice that the plant wilts or becomes stunted. To prevent sun damage, make sure to give Costus tonkinensis some shade during the hottest parts of the day. You can use a shade cloth or plant Costus tonkinensis near taller plants that can provide some natural shade.

If Costus tonkinensis doesn't get enough sunlight, it may grow tall and lanky, with sparse foliage. The leaves may also turn yellow or pale green, indicating that the plant is not producing enough chlorophyll due to lack of sunlight. To remedy this, try moving Costus tonkinensis to a sunnier spot, or prune nearby foliage to allow more light to reach the plant.