Basil is a fantastic herb to grow indoors. It can produce tasty and fresh leaves that will make your pesto or any other dish quite tasty. However, as banal as it might sound, watering is one of the parts where many people fail leading to basil death for either overwatering or underwatering.
An indoor basil plant should be watered accordingly to the planter size, soil type, plant age, and size. To understand when to water a basil plant, it is necessary to check early signs of basil wilting and check the soil below the surface. Indoor basil should be watered until the water starts dripping from the drainage holes.
Basil plants, if you do not live in a very cold or moist environment are relatively straightforward to maintain. Do not let bad watering behavior deprive you of healthy and strong basil.
There is not a precise amount of water to provide for indoor basil. This depends on the planter size, soil type, basil age.
If someone tells you one per cup per week, very likely this is are rule of thumb that, depending on the size and age of your plant, can even harm your basil.
Why? To answer this question, let’s understand what is the relationship between soil and basil with practical examples.
Suppose that you are using a potting mix heavy in compost (you should not do that). This potting mix has the tendency to absorb a significant amount of water and hold it. Suppose also that you are unlucky enough to have a young basil plant of a few inches height on a large planter (not a mistake, but something to avoid if you are starting out).
In this case, then, you have a large amount of soil that can hold liters of water. Do you think that a small basil plant can absorb liters of water? No. The soil will stay wet for a long time (if you watered it generously) keeping the basil roots constantly in contact with water.
How is that possible? Do basil roots extract water from the surrounding soil? Yes, it does, but at the same time, the water in the surrounding keeps pulled towards the drier area around the plants. Result? The roots are always wet.
This condition, called overwatering, followed by root rot, is the cause number one of dying basil indoor.
As a general rule of thumb, the larger the planter the less often your plant might need to be watered. At the same time, avoid too large planters. It is very easy to kill a basil plant.
That’s why, when discussing a good size for a basil plant I do not usually recommend more than 12 inches wide planter, if not for a large and developed plant.
For more check the full growing basil guide below.
The soil type makes a significant difference in how much and frequently basil needs to be watered.
Use clay soil taken from the outdoor garden and chances are that you are going to kill your basil after a month or less. Indeed, in many areas around the world (the UK included) outdoor soil can be clay heavy.
As discussed in our soil guide, clay suffocate many plants with “weak roots” (basil included). Clay is a very “dense” growing medium that behaves like a wall preventing the adequate exchange of gases that the roots breathe. In addition, water will be either on top of the soil surface (like a paddle) making the stem rot, or collected in undersurface pockets (rotting the roots).
Basil in clay just cannot be watered as basil in clay will not grow. The same applies to silt and any mixture of the two.
Of course, you might say, I will not use clay or outdoor soil for my basil. You might have used a good potting mix and your basil still died due to overwatering?
A potting mix with a high content of peat moss or compost or coco coir should be watered way less often than a basil plant a more gritty soil.
Coco coir, peat moss, and compost are well-known among gardeners and even scientists to increase water retention capabilities. This in general means that, differently from a more gritty potting mix, such growing mediums need to be watered way less often. They trap and hold way more water per volume.
The results prove that the soil on the plot with the dose of compost of 100 t.ha−1 showed an increase in the humidity. Organic matter, applied at the above-mentioned amount has a positive eﬀect on soil moisture retentionActa Universitatis Agriculturae et Silviculturae Mendelianae Brunensis
Compost can absorb from 60% to 145% of its weight of water.
Water Holding Capacity of the composted biosolids was the highest at 149 mL/100 grams and composted dairy manure was the lowest at 60 mL/100 grams – University of Texas
Despite Basil can be grown in a potting mix without the addition of gritty material, this can be challenging in providing the right amount of water for the basil plant that, quite often, might end up overwatered.
Growing basil exclusively in the sand is another bad idea. Indeed, sand is a growing medium with too high drainage capabilities that retains very little water.
Watering a basil plant in the sand is still possible but you might need too much water, way too often. This is not only environmentally friendly (due to the massive water you waste) but also very demanding.
Basil grown in the sand would require an excessive amount of watering and attention from teh gardener that is not feasible.
Sand has also the problem of not being able to retain nutrients, leaving the plant virtually with little to no nitrogen, potassium, and phosphorus to take on.
It is quite obvious that a small plant will absorb way less water than a fully developed one. However, many forget this detail by providing liters of water at once to their 2 weeks old basil plants. More water is not always better, especially for basil.
Basil plants (a few weeks old) will benefit from more frequent watering with a small amount of water rather than seldom watering with a large amount of water. This is even more important for small basil plants if in a large pot.
If you provide a massive amount of water, your basil plant will take a long time to absorb it.
This is not a problem if it was not for its roots. Basil plants are easily prone to root rot when their roots are constantly in contact with water. For healthy development, they should have the opportunity to go through a water and dry cycle (not too long though, more on this later).
You know how the planter, soil, and the basil plant itself affect the watering. However, the key question is when and how to water basil plants?
If there is one thing that I would like you to remember from all of this is this.
There is no precise amount of water or frequency by which a basil plant should be watered. This is because there are so many different variables that affect basil plant watering needs.
Hence, what should you do?
An indoor basil plant should be watered 1) at the first sign of wilting or 2) when the soil just an inch below the surface starts getting dry.
Have you never heard about it? Here I will tell you why
I define basil as a very expressive plant. Healthy basil loves moist soil (not waterlogged) and when it does require water (and none is found) the basil leaves will start losing more water than they absorb and so the stem.
In a few hours, the basil will start bending on itself and the leaves will look droopy and without life. No worries, this is normal and your basil is still fine (if you do not wait days before watering).
Once the leaves start drooping this is the right time for water. The plant is indirectly communicating this need through such wilting. The only thing necessary is to add water.
The basil leaves and stem will get back to life in as little as 2 hours. The leaves will be “meaty” and standing upright again and so the stems. Basil is an incredible herb.
Should you wait every time for the basil to wilt? Not at all!
Indeed, once you get used to your basil wilting and you know that every 4 days (for example) your basil needs water, you do not need to wait anymore for the first wilting signs.
Indoor basil needs more water in summer than in spring. This is because the higher number of daylight hours pushes the plant to produce more leaves and so increasing its water requirements.
Hence, the watering schedule should be adapted accordingly to the season (temperature and number of light hours).
This for you means to avoid sticking to the 4 days (for instance) schedule you found in April. After a few months, you should again let your plant tell you when it needs to be watered as the conditions might have changed. This also accounts for the growth of the plant!
Tip 2: Water The Basil When The Deep Soil is Dry
This is another mistake in watering I see often.
Indoor potted basil should not be watered based on how the superficial soil looks. A dry superficial soil does not mean that also the soil around the roots is dry.
Indeed, the superficial soil might be dry but where the roots take their water is the “deep soil” and not the superficial one. I am telling you this because it is not unusual to have the soil surface dry but the soil beneath it quite moist.
What can you do then? Easy, stick your finger 1 inch within the soil. What are the results?
- Is the soil sticky to your finger? Does it feel wet? If so then your basil does not need water;
- Is the soil dry at teh touch even 1 inch below? It is crumbling looking? In this case, your basil needs water. If it is not wilting it will be very soon.
This is another controversial topic among gardeners despite not being difficult.
Basil is an herb that is not meant to grow in rainy places (if not with excellent drainage). This is because it hates having “wet feet”. This problem is even more relevant for potted plants where the soil is limited.
Indoor potted basil should be watered even more carefully because the soil might not drain as well as the outdoor one.
To understand why this is the case and how you can easily check that, you need to imagine the soil like a sponge. After a certain point, the soil is “saturated”. This means that it cannot absorb more water. Any further water you add into it will leak out.
When the soil starts dripping from the planter it means that it had enough. Hence, there is no point in adding more water. This is usually too much for a basil plant. As mentioned before basil hates wet feet. This is even more critical if you have an oversized pot.
What can you do? Here the steps to water appropriately your basil:
- The first time use a measuring cup or something that tells how much water you are using
- Place an amount of water around a fourth of the soil volume. No need to precise here
- Pour the water into the planter
- Is the water leaking from the planter drainage holes? If so, the next water try to put a bit less
- If no, then you are sorted
The “quarter rule” is because many potting mixes can absorb around a third of their body weight in water. Hence, using for the first time an amount of water that is a quarter of their soil volume, places you on the safe side and you avoid overwatering the plant.
yourindoorherbs.com is part of the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites like mine to earn advertising fees by promoting good quality Amazon.com products. I may receive a small commission when you buy through links on my website