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Watering Cannabis Outdoors: Everything you Need to Know

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Watering cannabis plants outdoors
December 10, 2020
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Outdoor cultivation is not only undemanding and straightforward but also rewarding. After all, cannabis seeds, pots, soil, and water are all you need to get started.

Yes, you still need water. Just because you’re growing outside doesn’t mean that you can rely on rainwater for hydration. And if you want bountiful yields, you can’t just hose down the plants or use tap water straight from the faucet. Before we start, we also have an article on watering cannabis plants indoors as well.

Watering cannabis plants is also about timing and providing the right amount. Disregarding these two factors can slow or even halt growth, as well as significantly reduce yields.

Sounds complicated?

No worries.

In this article, we’ll tell you everything you need to know about watering outdoor marijuana plants. It includes:

  • Where to obtain your water
  • How to prepare the water
  • How often you water
  • How much water you should use

A Guide to Watering Outdoor Marijuana Plants

Cannabis plants need water to grow and survive. It acts as a conduit, delivering nutrients and essential minerals absorbed by the roots to the rest of the plants. It also plays a crucial role in vital plant functions, including growth, transpiration, and photosynthesis.

While generally resilient, marijuana plants cannot tolerate watering malpractices for long periods. You can avoid this problem by understanding the plants’ needs and knowing how to provide water. That said, if you want robust growth and generous yields, here are some of the factors you need to keep in mind.

  • Water source
  • The ppm, pH, and temperature of the water
  • Watering method
  • Frequency of watering
  • Volume of water

Step 1. Consider the Water Source

Before worrying about when and how to irrigate the plants, you need to secure some water first. Unfiltered tap water is the most common water source. Some might have rainwater collection systems. Both tap and rainwater will do, but you’ll have to filter it beforehand to make it suitable for cannabis plants.

Many growers swear by the reverse osmosis (RO) filtration system, which removes about 95-99% of the contaminants, including heavy metals and minerals. While it can be pricey, it is worth the investment and will provide you with an infinite supply of clean, usable water. It is particularly suited for those growing several plants or those who live in areas with hard water.

Step 2. Prepare the Water

Let’s get this out of the way. You should not use water – even RO water – as it is. Otherwise, you may interfere with nutrient uptake or the soil microbial activity. To be safe, prepare the water before every irrigation.

If your municipality uses chlorine as a disinfectant, let the water sit for 24-48 hours to let the chemical evaporate. If it has been treated with chloramine, you’ll need to run it through an activated charcoal filter before making the necessary adjustments.

Measure and Adjust the PPM Level

PPM or parts per million is a measurement of particles (including calcium and magnesium) suspended in the water. Cannabis plants only need around 100-150 ppm of minerals.

Tap water is about 170-390 ppm. RO water, on the other hand, contains less than 30 ppm of calcium deposits. Both do not sit within the optimal range and need to be adjusted.

Measure the ppm of the water using a TDS meter. If it is beyond the suggested range, purify it using a filtration system. Measure again. If it is too low, treat the water with cal-mag supplements until the reading reaches 100-150 ppm.

Measure and Adjust the pH Level

Aside from ppm, you need to adjust the pH level as well. Soil-grown cannabis plants flourish in a slightly acidic environment of pH 6.0 to 6.8. This time, you’ll need a digital pH tester or a multimeter to measure the pH value. Use pH up or down solutions to bring the pH to the ideal range.

Check the Water Temperature

Ensure that the water is at room temperature or about 70°F (21°C). If it is excessively warm or cold, the plants may get stressed out. It may also lead to nutrient problems, stunted growth, and fungal diseases. You can use a water thermometer or a multimeter to check the temperature.

Step 3. Decide How to Water the Plants

Your water is ready to go. The question is, how on earth do you even water outdoor cannabis plants? There are generally two ways to go about this – via hand-watering or drip irrigation.

Hand-watering

This is the traditional way of drenching the crops. It is just a matter of filling a watering can with balanced water. For the typical home-grower, it will suffice. In most states where outdoor cannabis cultivation is legal, after all, you can only cultivate up to 12 plants per household.

Watering Outside by hand

Note: Be sure to check the local marijuana laws and restrictions regarding the number of plants you can cultivate to avoid getting into trouble.

When watering, do not position the can above the canopy. Instead, soak the plants directly at the base. Do it slowly, ensuring that the medium is uniformly and thoroughly drenched. Keep at it until 10-20% of the water trickles out of the drainage holes. Furthermore, try not to wet the leaves so as not to attract fungi.

Drip Irrigation

If hand-watering already sounds tedious, then you might want to look into drip irrigation systems. These primarily consist of tubings and emitters and work by supplying water directly to the root system. It may also come with a timer to automate the whole process.

A drip irrigation set-up does have an upfront cost of hundreds to thousands of dollars – depending on how large the garden is. For this reason, it is more commonly used by commercial growers. It also requires regular cleaning and maintenance to avoid salt build-up and to keep it functional.

Step 4. Know the Right Time to Water the Plants

It is recommended to irrigate cannabis plants early in the morning before the sun has come out. Doing so presents many advantages.

  • Since it is relatively cool during this time, the water can penetrate the soil and reach the roots instead of merely evaporating into the air.
  • It ensures that the moisture is available for the plants throughout the day, helping them deal with heat and sunlight better.
  • It allows the plants to use the available nutrients more effectively. That is because many processes occur with sunlight – most notably photosynthesis.

Unfortunately, not everyone has the time to water early in the morning. You might have to prioritize work and other responsibilities. If this is the case, consider irrigating in the late afternoon instead. By then, there is still ample sunshine to let the plants dry.

Water droplets on cannabis plant

In that regard, make sure not to water right before nightfall. It doesn’t give the plants enough time to dry out. Damp leaves at night, in turn, can be a breeding ground for molds, mildew, and other fungi.

Watering in the afternoon when it is hot is not advisable either. The high temperatures will only cause the moisture to evaporate before being absorbed and used by the plants. It cannot be helped, though, if the plants appear parched midday. Avoid watering on windy days as well, as strong winds can increase the transpiration rate of the plants.

Step 5. Determine How Often and How Much to Water

Here comes the tricky part. As early as now, you should know that there are no hard and fast rules on the frequency and amount of watering. That is because several factors come into play, including climate, strain, pot size, medium, and growth phase, among others. You do have to take everything into account to know the appropriate watering schedule for your crops. That said, you might have to experiment – and make mistakes along the way – to master the art and science of watering cannabis plants.

When in doubt, water less often.

Climate and Geographical Area

When growing outdoors, the climate is undoubtedly the most important consideration. It rings especially true if you live in areas with extreme weather conditions. Make sure to adjust the watering schedule accordingly. In general, the hotter and drier it is, the more often you have to water.

Arid regions. Plants in dry climates typically have a rapid evaporation rate due to the intense heat. To compensate, you’ll most likely have to water the plants several times throughout the day. Otherwise, they may experience heat stress. The soil may also dry out and start cracking, which can damage the fragile roots.

Warm regions. Plants in temperate areas also have a quick evaporation rate – but not as severe as that of desert-like regions. Make sure to monitor the garden. Water the plants if they start showing signs of dehydration. If it is sufficiently humid, you might not have to water as often.

Cold regions. In cooler climates, the soil usually remains moist for more extended periods. As such, the plants might only require drenching every few days.

Plant and Pot Size

The rule of thumb is, the bigger the plants, the more water they need. And if you’re growing in containers, that is another thing to consider.

water drops cannabis leaf

Ensure that the pot is appropriately-sized. If it is too large, the water may stagnate at the bottom, inviting molds, mildews, and root diseases. It can also trigger overwatering problems. Too-small containers, on the other hand, may cause the plants to become root-bound, leading to stunted growth.

Note: If you do have to use an oversized pot – as is the case with auto-flowering varieties – be careful not to overwater the plants. You can reduce the volume of water per irrigation or water less often. You can also use air or smart pots, which offer better drainage and aeration than regular pots, making them harder to overwater.

Refer to the table below to have an idea of how much water you should give the plants depending on the pot size.

Pot Size Amount of Water per Irrigation
1 liter 0.25 liter
4 liters 1 liter
12 liters 3 liters
30 liters 7.5 liters

After being watered, the pots should feel very heavy. Consider lifting it every day to assess its weight. Once the container feels light, then you can water the plants again. Be patient if you follow this technique. It might take you some trial and error to determine if the plants need irrigation.

Growing Medium

To know if the soil needs some hydration, simply jab a finger 4-5 cm deep into the medium. If it feels dry to touch, then it is time to water the plants. If it remains somewhat damp, then wait a bit more. In most cases, you’ll be watering every 3-4 days. Other elements, of course, still come into play.

If it takes much longer than that – and if the water takes several minutes to seep out of the bottom holes – then you most likely have some drainage problems. Consider amending the soil with lighter substrates.

Once you do, the watering frequency may vary slightly. Coco coir and perlite, for instance, require daily watering at first. Eventually, though, you can start irrigating every 2-3 days. Again, check the weight of the container to confirm.

Growth Stage

Cannabis plants have varying moisture needs across each growth phase, demanding more water as they mature.

Seedling stage. Budding cannabis plants need minimum amounts of water at frequent intervals. That is because they do not have an extensive root system yet. Ideally, you should water twice a day. Start with a hand bottle spray, then switch to a watering can once they have rooted down.

Vegetative stage. During this stage, the plants experience an explosion of growth, particularly the roots, branches, and leaves. You might have to water every day to accommodate the rapid development. If the containers are large, though, you can irrigate every two days instead.

vegetative cannabis outdoors

Flowering stage. As the plants produce more buds, their moisture needs also increase. Typically, you’ll be watering every 2-3 days. But as harvest-time looms closer, the water requirements gradually decline before you harvest your buds.

Step 6. Know the Telltale Signs of Watering Problems

Bad watering habits and/or improper drainage may lead to either underwatering or overwatering issues. Both can compromise the growth and yields of cannabis plants. Knowing their early symptoms allows you to rectify the problems before they cause irreparable damage.

Underwatering

Under-watering often arises when you give the plants too little water, irrigate too seldom, or use too-small containers. Without enough moisture, the root zone will dry out, and the plants will eventually wilt.

Signs:

  • Drooping and/or wilting leaves
  • Brittle and papery leaves
  • Brown or dark spots on leaves
  • Burnt-looking leaf tips
  • Yellowing of new leaves
  • Yellowing of older leaves
  • Older leaves falling off
  • Pale leaves
  • Bone-dry and crusty soil
  • Symptoms of nutrient deficiencies

How to Remedy and Prevent Under-watering:

Dehydrated plants are easy to nurse back to health. All you have to do is water the plants immediately – and more often. Still, be extra careful not to overwater. You can also spritz some water on the withered foliage to perk them up.

Overwatering

Overwatering plants occurs when you water the plants too often, give them too much water at a time, or have insufficient drainage. Of the two, overwatering is more severe. It can lead to oxygen deficit, causing the decay of root tissues. If left unaddressed, the plants may even die.

Signs:

  • Drooping leaves
  • Firm, bloated leaves that curl inward
  • Yellowing of new leaves
  • Brown or dark spots on leaves
  • Burnt-looking leaf tips
  • Muddy soil
  • Presence of molds, mildew, and pests
  • Stunted growth

How to Remedy and Prevent Overwatering:

For oversaturated plants, the first thing to do is water less frequently. Keep at it until the plants recover.

Remember, when irrigating, the water should not pool on top of the medium. It also should not take a long time to drain out. If so, consider drilling more holes at the bottom of the pot. You can also mix the soil with aerating materials to improve its drainage.

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