A must-grow herb for millions of gardeners, figuring out how often to water basil can be a challenge. Maintaining the ideal watering frequency can mean the difference between a healthy, productive basil plant and one that is wilting, discolored, and suffering. In this article, I’ll discuss everything you need to know when it comes to watering basil, including how much water to use, how often to add it, and what signs to watch for to prevent both over- and underwatering.
Where to grow basil
Before we dive into watering tips for basil, I’d like to quickly go over the best conditions for basil growth. This is important because if you aren’t growing this herb in ideal conditions, whether or not you water properly isn’t really going to matter. If basil doesn’t have the conditions it needs to survive, no amount of water is going to make a difference. Here’s a quick Basil 101.
Basil (Basilicum ocimum) is a member of the mint family. Like other herbs in this family, it enjoys warm weather and direct sunlight. Basil is a tender annual that does not tolerate cold temperatures. The foliage turns black with even the lightest touch of frost. Wait to plant it outdoors until the danger of frost has passed. In my Pennsylvania garden, mid to late May is the perfect planting time.
If grown in the shade, basil will not thrive, nor will it grow well in cool conditions. At least 6 hours of full sun and high temperatures are best.
Now that you have a handle on the best conditions for growing basil, let’s talk about watering the plants.
Signs that basil needs to be watered
Like most other plants, basil exhibits clear signs when it needs to be watered. The leaves wilt, the stems sag, and the entire plant looks droopy and weak. If not watered promptly, you may find the basil leaves turning black.
Unfortunately, by the time a basil plant exhibits these symptoms, it is already stressed. Stressed plants are more prone to pest infestations and diseases like basil downy mildew. They also tend to bolt (produce flowers) prematurely. Basil that has bolted has a slightly different flavor, so most gardeners do everything they can to prevent their basil from going to flower. Keeping the plant well hydrated and unstressed is helpful in that regard, though most gardeners also pinch off the flower buds as soon as they start to develop. The trick to growing amazing, properly hydrated plants is to know how often to water basil so the plants never become stressed in the first place.
This may lead you to wonder if you should put your basil on a strict watering schedule. The answer to this is no. How often to water basil, how much water to add at any given time, and what time of day to add it depends on two primary factors: the age/size of the plant and where it is growing. Throughout this article, I’m going to talk about both of these factors in turn and how together, they influence basil watering.
The best time of day to water basil
If you want to be a responsible gardener, opt to water your basil plants in the morning. You’ll lose less water to evaporation. Plus, watering basil in the morning means the foliage will have time to dry off before nightfall. Wet foliage at night often spells disaster for basil since the spores of various fungal diseases thrive in wet conditions on still summer nights (plus, slugs!).
The second best time to water basil is in the evening. However, when watering in the evening, it’s important that you target the water directly at the soil around the root zone of the plant. Try your best to keep the foliage as dry as possible.
Is it better to water basil with a hose or a watering can?
Moist soil is the end goal, and as long as you manage to make that happen, your basil plants won’t care whether they receive their water from a watering can or a hose nozzle. That being said, remember to keep the foliage as dry as possible to prevent disease. Overhead sprinklers aren’t the best idea for watering basil since there’s no way to use them without getting the foliage wet. If you have a choice, use a hose nozzle directed at the soil level, drip irrigation, a soaker hose on the soil surface, or a watering can aimed at the base of the plant. Obviously you can’t control the rain, but do what you can to control the delivery of any irrigation water.
What kind of water to use
How often to water basil and how much water to add are much more important to focus on than what kind of water to use for the job. Tap water is fine. Rainwater collected in a rain barrel, bucket, or cistern is great, too. There is no need to water your basil with any kind of “fancy” water.
How often to water basil based on the plant’s age
As mentioned previously, how often to water basil depends primarily on two factors: the age/size of the plants and where they are growing. Let’s talk about how the plant’s age affects watering frequency first.
Young basil seedlings require much less water than fully mature plants. Newly planted basil transplants should be watered in thoroughly immediately after planting. A half-gallon of water per plant does the trick. Water basil seedlings with another quarter- to half-gallon of water a few times a week thereafter when no rainfall has occurred. The small sprouts will easily drown if too much water is applied at once.
As the plant grows, you’ll have to make more frequent watering efforts. The target for mature plants is one inch of water per week (per square foot). The average basil plant’s root system extends to a width of about two feet. To apply one inch of water to that amount of space (4 square feet) each week, it requires about 2.5 gallons of water applied to the root zone slowly enough for it to fully soak in and not run off. In extremely hot weather, this amount needs to increase due to evaporative water loss.
How often to water basil based on where it is growing
The next way to determine how often to water basil is by considering where the plant is growing. Watering basil growing in a pot requires a slightly different technique and frequency than basil plants growing in the ground. Let’s look at the special considerations for each location.
How often to water basil growing in a pot
Potted basil plants require more frequent irrigation than basil growing in the ground. There are multiple reasons for this:
- Peat moss-based potting mix is lighter than garden soil; it’s also better draining and dries out more quickly. This means you have to water a basil pot more often than basil growing in the ground. Tip: If you mix compost in with the potting soil, it won’t dry out as quickly.
- Pots made of certain materials are porous, such as a terracotta pot. This means that water is wicked out through the pores in the pot, causing the soil inside to dry out more quickly. Tip: Ceramic and plastic pots won’t dry out as fast as terracotta.
- The leaves of basil plants growing in pots often cover the soil, shielding it from rainfall. If no rain makes its way into the pot, you’ll need to water it more often.
Smaller pots dry out much faster than larger pots, so how often to water basil growing in a pot depends on the size of the pot, too. The best way to know when to water is to stick a finger into the potting soil as deep as you can (a fingers depth) and feel how dry it is. You should also pick up the pot to see how light it is (dry soil weighs much less than wet soil).
When the soil is light and dry to the touch, it’s time to water. Hold a hose or watering can at the base of the plant and distribute the water directly to the root zone. If the pot has drainage holes (and it definitely should!), it’s impossible to add too much water. The excess will simply drain out the bottom. Overwatering potted basil occurs when you water too frequently, not when too much water is added at once. Don’t water your pot again until the “finger test” and the weight of the pot tell you it’s time. Smaller pots may need to be watered every day, while larger pots with compost in the mix may only need to be watered once a week.
How often to water basil growing in the ground
It’s a little more challenging to determine how often to water basil that’s growing in the ground. Basil pants that have a layer of mulch protecting their roots won’t dry out as quickly. One to two inches of shredded leaves, grass clippings, or straw prevents moisture loss and lessens watering chores. The type of soil you have matters too. Basil growing in sandy soils needs to be watered more frequently than basil growing in clay soil.
All that being said, I don’t want to over complicate it. The “finger test” works for in-ground basil, too. Stick your finger into the soil; if it’s dry, it’s time to water. It’s much better to provide a deeper, more thorough watering than it is to do light, shallow waterings that promote shallow root growth. If you want deep, self-sufficient roots, you’ve got to water deeply.
Remember, the target for mature basil plants is one inch of water per week (per square foot). To apply one inch of water to the amount of space a basil plant requires (about 4 square feet), plan to provide 2.5 gallons of water, slowly and deeply, once per week (if the plant is young or not yet established, break that into two watering sessions of 1.25 gallons twice a week). And keep in mind that really hot weather means the plant will require additional water above and beyond that amount.
How much to water basil when growing indoors
If you are growing an indoor basil plant (preferably under grow lights to ensure it receives enough hours of sunlight), it won’t require as much water as an outdoor plant. Indoor basil plants don’t use as much water so the frequency of waterings is reduced. The “finger test” works like a charm here too, as does feeling the weight of the pot. In general, one gallon per plant once a week for mature plants is enough.
Overwatering basil plants
While underwatering is far more common than overwatering, I do want to mention some signs of overwatering so you’ll know what to watch for just in case you go a little overboard. Unfortunately, when basil is overwatered, root rot can be the result. The signs of overwatering look a lot like underwatering. Basil leaves droop and wilt, and there may be yellow leaves at the base of the plant. For potted plants, don’t let water sit in a saucer beneath the plant.
If you suspect overwatering is to blame, reduce the frequency of your waterings and make sure to perform the “finger test” before deciding whether or not to water.
Fertilizing basil when you water
If you’d like to ensure your best basil harvest ever, consider adding a liquid organic fertilizer to your irrigation water once every four to six weeks. Do not use a fertilizer that promotes blooms. Instead, choose one that is slightly higher in nitrogen, which encourages green, leafy growth. That’s exactly what you want from your basil plants! Mix the fertilizer in with your irrigation water in a watering can or bucket and distribute it onto the root zone of your plants.
Whether you grow sweet basil, lemon basil, Thai basil, spicy globe, or any of the other amazing basil varieties available today, proper watering is key to your success. Use these tips to determine how often to water basil and you’ll definitely be headed in the right direction.
For more on growing beautiful basil, please visit the following articles:
- Growing basil from seed
- What to do when basil leaves turn yellow
- How to prune basil for big, bushy plants
- Tips for growing basil from cuttings
- Types of basil to grow
- Perennial basil and its relatives