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All You Really Need To Know About Watering Outdoor Potted Plants

Watering is the number one problem that most people have with plant care. Watering is also one of the top questions people ask me at the garden center. Most people who don’t ask assume it is self-explanatory and they should already know. No, it is not self-explanatory, and there is no reason why you should already know. 🙂

  • Under-watering
  • Over-watering
  • How much to water
  • How often to water

Watering potted plants has a few basic principles.

  • Water thoroughly, 3 times in a row, until the potting soil is holding as much moisture as it can. Even if water is exiting out of the drainage holes the first of the three times you water, still continue to water for the three times in a row. This ensures all of the potting soil is moist.
  • Wait until the soil has mostly dried down again.
  • Water thoroughly again.
  • Check hanging baskets and smaller containers outside daily.
  • Check indoor plants weekly. A pattern will emerge for your plants, in your soil, in your spot.

Start here, I will explain more as we go.

Water Thoroughly

 Sounds simple, you just add water until it runs out the bottom, right? No, not really.  Potting soil is a lot like a sponge. When dry, you have to do more than run a stream of water over it until the water runs over the sides to get wet again. However, when a sponge is damp, you can.  When saturated, any more water dripped in the top will move through and push water out the bottom, not holding anymore.

Watering three times works like this.  The first time, the water will find the quickest path through and out.  This can leave completely dry areas of soil, that can damage roots.

The second time you add water, the water will flow immediately through the already damp portions, and expand them and dampen more soil along that route.  

The third time is usually the magic number to moisten all of the remaining soil in the pot.

If you have let your plant dry down too much (think of a dried out, hard sponge) then soaking your pot in the sink or a bucket with a few inches of water is in order.  The potting soil will have pulled away from the sides of your container, and the first step of a damp trail down through the soil does not happen.  The water simply runs down the cracks.  re-routing from the slower path through the potting soil entirely.  

As a side note, don’t let your potting soil get so dry that it shrinks and pulls away from the container.  It is doing the same thing from the plant’s roots, damaging the fragile microscopic root hairs that do all the work. 

Wait Until Your Plants Needs Water Again

Let’s get back to our sponge analogy,

What happens when you stand that saturated sponge on its end, so it is tall? In a moment, the top is drier than the bottom. The bottom will still be saturated while the top is only damp.  As the sponge dried further, the top can be mostly dry and the bottom still damp.  When determining when to water again, you want the soil not to be saturated in the bottom of the pot, but before it all has pulled away from the sides.

The larger the pot, the longer it takes for this to happen. As far as the outdoor plant is concerned, usually the larger the pot the better, for crowded containers.  

If choosing between two pots that fit your budget and design proportions of your space, pick the larger pot that holds the most potting soil in the root zone. For combination containers of annuals and perennials, 10-24 inches, small trees, and shrubs can go down 36 inches or so. Much deeper than that usually is not necessary. The roots grow further horizontally than deep for most plants when given a choice, but I digress….

When the container has reached that point of needing water again. It needs water again. Don’t wait if it is in the sun. Just do it now, your plants will thrive rather than just survive.



Check To See If Your Container Needs Water Again.

Check to see if your SOIL needs water. If your PLANT needs water, you are already setting it back, for your plants to thrive rather than survive, it should not dry out completely.  Speaking of typical water preferences of slightly damp soil, otherwise known as well-drained, evenly moist soil. 

If your plant wilts from dry soil, it is too late, you are relying on the plant’s fighting for survival, not thriving. Also, return and re-water a couple of hours after you initially watered your three times (or soaked the pot in the sink for a while). This is because the plant has drawn up into it’s leaves a portion of the water the soil was holding, leaving you with a less than ideal ‘reserve’ of water in the soil.  Meaning you will have to water sooner than you otherwise would, throwing off your watering pattern.

Let’s use a gas tank in your vehicle as an analogy. The numbers will be simplified for ease of explanation. Let’s say you have a 10 gallon ( or Liter) regular tank, this is your soil. You have the benefit of a 1 gallon (or L) reserve tank so you don’t run out, that is your plant. You know you can drive 10 miles before you run out of gas in your regular tank. You fill it up every other day and you know you have 10 miles before it runs out, you don’t like to dip into your reserve EMERGENCY tank unless it is an emergency, so that does not happen that often.

This day you did, you went 10.7 miles and used part of your emergency reserve fuel (plant wilted from the soil being too dry). When at the station, you only refilled 10 gallons( your soil) and your reserve tank automatically topped off (your plant refill with the water it needed, perked up). This leaves your tank (soil) short of a full fill up. What happens when you try and go your usual 10 miles? You run short and use your emergency reserve again.

Routinely dipping into your plants emergency reserve of moisture makes a plant fight for survival, rather than growing and flowering abundantly, thriving.

Water before your plant wilts from lack of water. Check your SOIL for when you need to water, not your plant.

There are exceptions to most rules, and there are to this one, however, unless your plants are an exception, they will fall into these rules for watering.

Check For Watering Weekly, Daily….

As I mentioned above, CHECK for watering, usually weekly for indoor plants, and daily for outdoor potted plants. Sometimes twice daily for hanging baskets in the sun.

Notice I did not say to water, I said check. No one can tell you how often to water and how much to water, without experiencing your exact planter. We can guide you on how often we expect it might need it, and rely on that window of time for watering.

How much and how often to water for your plants to thrive will depend on several factors. What the exact components of your potting soil, what plant you have and volume of leaves in relation to the volume of soil. What is your pot made of? Terra cotta that allows water to evaporate from the sides of the pot? How long has the pot been used, and have the pores in the pot clogged with fertilizer salts yet? Exactly how much sun does your plant receive and how strong is the sun it receives? How much air circulation (wind) and at what percent total humidity does it contain. I could go on…

That is why no one can accurately tell you exactly how much, and how often to water. Understanding the concepts and what to look for will allow you to apply that knowledge to many different situations. Like a recipe can be given to an experienced baker and a novice. Same recipe, different results that come from experience and an understanding of the concepts and science behind the recipe.

I know not everyone likes to geek out on the science behind plants, soil, and horticulture. I hope I have given you some ideas about the science behind watering and the concepts, so you can apply them to your specific plant situations and help them thrive!

What Water Need Type Is Your Plant?

Most plants are grouped into three categories. Water needs are high, medium or low.

High water needs:

These plants like readily available water at all times. No drying out. This does not mean the plants like to be submerged or saturated all the time. That is a very special group of plants, bog or water plants, not included in the basic three. Examples are elephant ears, Tut cypress, most ferns, and others. These are plants that seem like they readily wilt the moment the soil is not damp to the touch. Water these when the soil is like a squeezed out sponge. Overcrowding in the pot will exasperate the issue, so leave them a lot of room at the table.

Medium water needs:

These plants are as described in the article, and encompasses a large portion of plants you will be growing in containers.

Low water needs:

These plants are rock-stars for most of us in containers. These plants like to dry out between waterings. Usually, these plants have water-storing built into the plant. Either in their leaves, stems, or roots. Plants like portulaca, asparagus fern, and sedum.

Careful when looking at tags. Plants that have low water needs when planted in the ground because they have an extensive root system, are labeled the same, low water needs. However, these are not as well suited for containers because the extensive root system works against your container. It pushes out and replaces the potting soil reducing the total amount of moisture your container will hold, and they will bully your other plants. push them against the wall and steal their lunch water.

Lantana is a great example of this. I love them in the ground, but not in a mixed container. By August, the hottest and driest month of the year, that container is all root, no soil to hold water, and it has choked out or bullied out the other plants in the container.

Click here to read a short bit I wrote on if plant saucers are a good idea..


Toni has a bachelor degree in Plant & Soil Science, has lived, gardened and growing all over the US, in Vermont, Tennessee, Idaho, coastal North Carolina and Virginia. She has been sharing her knowledge through writing, one on one consulting and talking to anyone who wants to listen at social gatherings everywhere : )

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