Disclaimer: Some links found on this page might be affiliate links. If you click an affiliate link and make a purchase, I might earn a commission. As an Amazon Associate I earn from qualifying purchases.--
Wish you could find a Boston Fern watering guide that would tell you exactly when to water, how much, and how to tell when something is wrong with your plant?
You will not find it.
What we can do is provide the guidance to inform you of what a Boston Fern needs, what effects its hydration, and how to tell when dehydration or (more often than not), over-hydration is a problem, and how to go about rectifying an overwatering problem.
Getting to Grips with the Drinking Habits of the Boston Fern
The Boston Fern dates back centuries. In two of the most viewed primeval films, The Land Before Time, and Jurassic Park, ferns feature as the predominant ground covering in tropical rain forests.
Locations where this grows are in warm and humid environments, surrounded by falling leaves and twigs that nourish the soil through natural decomposition that enriches the ground with nutrients.
The surrounding foliage from other plants provide higher than average humidity, and overhead canopies on trees protect the ferns from direct sunlight.
Unsurprisingly, these are renowned as tropical plants, but unlike the primeval versions that would self-seed, modern ferns have adapted to self-reproduce via spores on the underside of their fronds.
In this regard, the Boston Fern is one of the easier fern plants to grow because less water is needed to support reproduction.
Easier is not the same as easy. The Boston Fern can be a finicky plant for beginner growers because if its needs aren’t met, it will not grace you with gorgeous sword-like lush green fronds. The distinct shape of fronds on Boston Ferns is why it is often referred to as a Sword Fern plant – we are discussing the same plant!
Instead of the forestry and tranquil green fronds, without sufficient watering, the fern is likely to display limp foliage of dull uninspiring colors from pale yellow to dark browns fronds.
The tricky part is juggling the balancing act between how much water is just enough, too much, or barely enough for the fern to survive.
How much water a Boston Fern requires depends entirely on the location it is grown.
You have to grow Boston/sword ferns in a location that they prefer. That is not always where you want to grow them.
As an example, you may learn that the sword fern is among the best low light indoor plants to use as a feature display on a side table. Trouble is, if the humidity isn’t there, the fronds on ferns turn brown or yellow.
Location is pertinent to get right because without the right balance of light and humidity, it will be difficult to meet the watering requirements of this specific fern plant.
To meet the needs of a Boston Fern, mimic the conditions of a jungle floor. Do that by providing partial, and dappled sunlight, plenty of shade, and a dense substrate for the shallow roots to absorb nutrients in the soil or potting mix.
The three areas to consider growing Boston Ferns are indoors, or on a south facing outdoor porch, or in a hanging basket where it can get full sun in the morning.
For each of the locations, the watering methods can be slightly different and there are various approaches you can take to test if the soil has enough moisture content or if the plant needs to be watered.
For each of the locations, the best practices for watering Boston Ferns are described below.
A watering Guide for Boston Ferns Grown in Hanging Baskets
The Boston Fern is considered among the best hanging fern varieties there are. It has the growth potential to reach 3 ft in width with an equal trailing length.
The reason these are the superstars for hanging baskets is because of their splendid trailing habit.
It creates a terrific illusion. It’s like having the mini versions of palm trees without the trunk. The fronds trail over the basket in a neat bunch that look like a top of a tropical palm.
Ideally, these plants get started in containers, then get transferred to a larger hanging basket (8” to 12” in diameter) for outdoor display where they benefit from more exposure to dappled sunlight right around the plant, rather than having to be constantly be rotated indoors to get sunlight to each frond.
As with all plants, the hotter it is, the more water it will require. Shade is an important aspect of Boston Fern care, however, even in the shade, the heat of afternoon sunlight will cause water to evaporate at a faster rate. If you start to notice curling, or some fronds yellowing, it can be a symptom of drought.
Before watering, check the soil moisture level. You can do this using a moisture meter, by poking your finger into the soil to feel its moisture content, or push the container upward to feel its weight.
The weight check is the easiest. Each time you water the plant, feel the weight by pushing up on the basket.
Due to the heavy weight of water, when a hanging basket is needing water, it will feel much lighter. Of course, to understand if the weight has decreased, you need something to compare it to which is why you should familiarize yourself with the weight of a freshly hydrated hanging basket.
The substrate for Boston Ferns in hanging baskets needs to be well draining. Soil-less mixtures are preferable, which usually consist of peat, pine bark and vermiculite. This combination is fast draining. If the substrate is retaining water for too long, it risks suffocating the delicate root system.
The potting mix should fill the hanging basket to one to two inches beneath the lip of the basket.
When watering, it is important to water the substrate and not the fronds. That one to two inch gap between the substrate and the edge of the basket lets you water the base deeply. Provided the soil-less mixture has sufficient drainage, excess water will easily filter through with just enough moisture content being retained.
In the hottest part of the day (12 pm to 3 pm), should you notice the plant looking distressed, resist the temptation to water it, but instead mist the fronds to raise the humidity levels. Do this with tepid water. Not cold water as that can stress the plant or even put it in a state of shock.
The Boston Fern can only be kept in hanging baskets outdoors, all-year, in warm climates. Typically, USDA zones 9 to 11. Elsewhere, it will need to be brought indoors for overwintering. Indoor hanging baskets with Boston Ferns in the winter require far less frequent watering.
Unsure where to put them? Read 10 creative ways to hang plants from the ceiling.
Adapt your watering frequency to the environment the hanging basket is located in.
As an example, a Boston Fern hung in a bathroom will need less watering than one that is hung in an east-facing conservatory or near the window of a garden summer house.
Watering Boston Ferns Outdoors
The watering requirements for outdoor Boston Ferns depends on whether it is grown directly in ground soil or in a container.
Container grown Boston Ferns always need more watering than those planted in ground soil because soil holds water for longer.
In a container, the advantage is using soil-less mixes to improve drainage. In ground soil, it is imperative to check the existing soil moisture level before adding more water. Boston Ferns have shallow roots so the top half inch to one inch of soil is best to be dry-to-the-touch before watering.
The most critical element with ground soil is maintaining moist soil while preventing it from becoming damp by adding too much water.
How much water needs to be added depends on the quality of the ground soil. Clay soil, which is considered to be a heavy soil, holds high levels of water. This needs to be watered less frequently than sandy soils that are much faster draining.
- Sandy soil require watering at least once weekly.
- Clay soils usually require watering every couple of weeks, provided there has been no rainfall.
- Container grown Boston Ferns, such as those potted up in decorative planters placed on a porch always require more frequent watering. Typically, every five days, although depending on the temperatures, that can be decreased to once every 10 days. The smaller the container, the more watering will be required.
Keep an eye on the soil moisture content when temperatures are constantly hovering at or above 75oF (23oC). At these temperatures, water evaporates at a faster rate.
The brighter the sunlight and the hotter the temperatures reach; the more Boston Ferns need to be watered.
In garden soil, use the finger test method to check that the soil is dry to at least a half inch before adding water.
If you aren’t sure what texture you should be feeling, prod the soil with a stick, such as a twig. If it sticks to the stick, it’s moist enough. If it doesn’t, it’s dry and could do with a drink.
The soil needs to be kept moist, but never damp. Remember that the Boston Fern is a shallow rooted plant. If there is water pooling on the top soil, it is likely to starve oxygen to the roots restricting air flow.
In pots, just like with hanging baskets, you can check the weight of the pot. When water is lacking, the container is lighter.
Another way to check that Boston Ferns’ watering requirements are being met is just to pay attention to the color of the substrate. Dark brown soil is wet, and pale brown is drying or drying out.
For container grown Boston Ferns outdoors, kept in sunny locations, it can be beneficial to double-pot your plant. By double-potting, you can line the base container with sphagnum moss, which retains moisture.
During the peak of summer, the water evaporation increases humidity in the immediate surroundings of the plant. This can save you having to mist the plant two to three times daily, and reduce the risk of overwatering the substrate.
Watering Boston Ferns Indoors
With Boston Ferns indoors, watering requirements vary based on the climate and the size of container. The smaller the container, the more often it will need to be watered.
In all cases, indoor plants need to be watered more than those kept outdoors. Keep that in mind for outdoor grown Boston Ferns brought indoors for over wintering.
The humidity difference inside is huge. The simplest way to remember it is that the lower the temperature is outside, the lower your indoor humidity is. The air indoors is always drier.
Boston Ferns needs to have localized humidity at 50% and above. For that reason, Boston Ferns need not just watering, but also the humidity levels to be raised.
An effective way of raising humidity enough for a Boston Fern is to place it atop a pebble-lined tray. Gravel bases retain moisture, which gradually release water vapor throughout the day. Mini plant humidifiers can also lend an assist, as can grouping multiple plants close together.
The active growing season is April to September, which is when Boston Ferns require the most frequent watering.
In the winter, the growth rate slows. You will notice the soil takes longer to dry. During the spring and summer, indoor plants may need to be watered every few days. Over the winter, that can be reduced to one watering every other week (bi-weekly).
It is always best to err on the side of caution and wait until the plant needs a drink before you water it.
Test that by prodding your index finger into the soil to feel its moisture content. It should be moist, not wet. Preferably, the top two inches completely dry before watering.
When you do water, allow excess water to completely drain through the container’s drainage hole(s). Especially if you are placing it in a decorative planter (double potting), as water draining into the outer container can result in the base sitting in standing water.
Overwatering a Boston Fern, or letting it sit in standing water, will lead to root rot. In most instances, that will kill the plant. The roots are shallow, rot easily, and is difficult for the plant to recover from.
The earliest signs of overwatering are the fronds turning yellow and wilting. If you see that happening, cut back on watering, check that the container’s drainage holes aren’t blocked, which can happen if the plant becomes root bound.
To fix root bound plants, it will need to be repotted in a suitable sized container at least one to two-inches bigger in diameter than its current pot.