Water is vital to a plant’s existence.
The average garden plant is around 90% water and that water plays a pivotal role in just about every biological and physiological function in that plant. Water aids the process of photosynthesis, it works as a solvent to move nutrients throughout the plant’s system, it’s a medium for various biochemical reactions, it helps maintain proper cellular pressure for structural integrity and it helps regulate transpiration.
Having access to the proper amount of moisture is key to plant development and, as gardeners, it is often our job to help our plants with this. This is especially true in raised planter beds where we have complete control over the growing environment. But like many things, too much water can also do harm.
So how do we know when plants need water and how much is enough?
There is no substitute for experience, and with time you’ll have a keen eye for just what your plants need and when. In the meantime, there are some key things to consider when addressing your garden’s water needs.
Look At The Signs
In conventional gardening, soil is the medium by which most plants acquire moisture to support their systems. Our plants use their roots to draw moisture out of the soil along with the various nutrients available. It sounds pretty obvious, but dry soil is an indicator that your plants aren’t getting enough water.
The surface of soil dries out faster than it will below the surface, especially soil in direct sun or subject to windy conditions. To protect soil from losing too much moisture through evaporation at the surface we can use mulches and covers which help hold moisture in the soil. Careful though, the surface may tell a different story than what’s going on below.
Soil composition plays a heavy role in how much moisture is held in the soil and for how long. You want to have soil that is loamy, with a good amount of organic material (compost) to absorb moisture. A soil that is too sandy or grainy will not hold water and a soil too thick or clay-like will not drain well. If you’re constantly chasing soil moisture issues, work on your soil composition.
A plant will often tell you when it’s not getting enough water. Look for obvious signs of stress like decreased growth, small or off-color leaves and decline at the extremities of the plant. These can all indicate that a plant is dying of thirst.
Plant stress isn’t always related to dryness. Too much water can also cause a plant to suffer. Overwatering or poor drainage can result in a plant’s root system suffocating. Root activity will slow down and the plant will no longer be able to draw in enough water and nutrients to maintain itself. Similar wilting and yellowing will occur as well as decline at the lower levels of the plant and along the main stem. Root rot is also a possibility if the soil is not allowed to dry out.
Consider the Plant
Not all plants have the same watering needs. This is especially true in arid region plants. Arid region plants, or desert adapted varieties, are plants that survive well in low water environments. If your low-water plants are showing signs of stress, it’s likely due to overwatering. Succulents and cacti are universal examples of this, but many edible plant varieties prefer drier soils as well. Some common herb varieties that prefer dry, well drained soils are Rosemary, Sage, Thyme and Oregano.
A plant’s root structure plays a big role in it’s watering schedule. Common leafy greens like Arugula and Bibb Lettuce have shallow root systems and may need to be watered more often because the roots don’t reach deep enough into the soil. It’s also important to water your greens in the morning so the plants can make use of the water they’re given before the transpiration process halts their ability to draw in water.
It’s important to note the difference in water needs between new transplants and mature, established plants. The more developed the root system, typically, the less often a plant will need supplemental water. The idea is to get a plant’s root system to grow robust and deep to reach an ample supply of moisture on it’s own. But in the meantime, new transplants will need help since their immature root systems will be limited. Deep watering, less often can be good for transplants as it will spur the root system to grow deeper as it reaches for available moisture.
Know How To Water
In the act of watering itself, it’s important to remember that you’re not really watering the plants. You aren’t directly feeding your plants the water they need. Instead, you are watering the soil. You’re trying to saturate the soil with enough moisture that it will be able to hold that moisture long enough for the plant’s roots to take advantage of it.
Deliver too much water too fast and it will simply drain away, leaving you with soil that dries too quickly and is depleted of nutrients. Don’t deliver enough water and you won’t see full saturation of the soil. Too little water also doesn’t allow for proper drainage and can lead to the build-up of potentially harmful minerals in your planter beds.
How much you water depends greatly on a variety of factors including the type of plant, soil composition, existing moisture, ambient humidity and the location of the planters. Your watering schedule should reflect these variables. Not all planters should be watered the same.
In general, you want to water deep and slow with enough water to saturate the soil to the lowest part of the roots of your plants. Then let them dry out a little, maybe even for a day or two, to encourage the roots to grow deeper and get stronger. Then give them another good soaking. This will give you a loose watering schedule that is very specific to the unique conditions of each individual planter.
So, how much moisture is in your soil? Is it enough?
We can use a moisture meter to specifically and scientifically pull empirical data on how much moisture content can be found in your soil. Using a moisture meter at various depths and in various areas of the planter bed will give you a more complete picture of how moisture is distributed.
Most moisture meters will translate the data for you and a scale of Dry-Moist-Wet. Within the first 24 hours or so of watering your meter should read “Wet”. If it is reading “Moist” within the first 24 hours you’re likely underwatering the plant. Check it every day until the meter reads “Dry”, then water it again within a day or two.
The moisture meter is great for getting a solid reading, but often times a simple “finger test” can be just as effective for judging soil moisture. Using your longest finger, dig it into the soil to the knuckle (about 3 inches). Feel for moisture in the soil at the end of your finger. Remove your finger from the soil and look for signs of moisture, dampness or wet dirt on your fingertip. If it’s dry then it might be time to water.
Tips for Proper Watering
Water in the morning – Watering early will help the soil absorb water before mid-day heat has a chance to evaporate what’s on the surface. It also allows your plants to take advantage of as much moisture as possible before shutting down transpiration.
Water deeply – Watering slowly and deeply will allow for better saturation into the soil and increase available moisture for your plants. It will also allow your soil to hold the water longer and increase the time between watering intervals. Remember, you are watering the soil to get moisture to the plants roots. Shallow watering at the stem or on the leaves is not helpful.
Minimize evaporation – Use mulch, plastic, landscape fabric or ground covers to shade and protect your soil from the heat of the sun to reduce evaporation. This allows the surface to dry out much slower which will help maintain overall moisture throughout the soil.