Although watering potted plants may seem a fairly easy task it can be ineffective if not done properly. It is the most important task in keeping your potted plants healthy. Correct planting techniques, potting medium, fertilization, and pruning are extremely important, but without correct watering these will make little to no difference in the plant's health. Although most potted plants need water to survive, their requirements vary as far as the amount of water specific plants need. Whether they require a large amount of water or very little the two most important factors in correct watering is being consistent with watering schedules and making sure all the potting mix is equally moist throughout the container. Varying lengths of time between watering along with too much or too little water can cause plant stress leading to poor health and a plant less resistant to pests and disease.
Watering potted plants until water drains from the bottom of the pot is a good practice. This watering helps to leach or flush out excess harmful salts, fertilizer residue and other toxic build ups in the soil that can harm a plant over time. Unfortunately just because water has drained from the pot's bottom it does not mean all the soil in the pot is being leached of harmful build ups or the pot's entire soil has been equally moistened throughout the container. Years ago I found that although I was watering many potted plants every day during the summer months some still had constant wilting, drying leaves, stunted growth, or just poor unhealthy appearance. It wasn't until I renewed the pots with new plants that I observed half of the pots planting soil was dry or unevenly moist throughout the pots. Not only were the plants not recieving the moisture they needed but without this moisture the plants were unable to absorb any nutrients they required through fertilization.
Types of materials pots are constructed of, quality of potting soil mix, planting techniques, size, and shape of pots or containers all play a part in the plant receiving the correct amount of moisture. These factors of course would make for another article in themselves. Hopefully a few tips on watering potted plants that I use will help to keep your planting medium thoroughly watered evenly throughout your pots.
Realizing a few simple mistakes I was making has kept many potted plants through the years from being added to my compost pile prematurely. Many times your watering of the soils surface may run quickly out the bottom of the pot, wetting very little of the pots soil content. Many soil mixes will shrink or contract as they lose moisture creating a small gap between the soil and sides of the pot or container. As water follows the path of less resistance it will quickly run down between the side of the container and potting soil with very little soaking or penetrating into the soil. This is more apparent when the potted plant is located in warm sunny locations. As water quickly passes through the gap around the pot and cracks created throughout the soil as it dries it may not have enough time to wet the dry soil allowing it to penetrate its surface. I'm sure many have seen how hard and long it takes for water to moisten and then penetrate into dry soil mixes especially those containing a large percentage of peat moss. Explaining the forces of gravity, cohesion, and adhesion that affect movement of water into and through the soil would take more written pages than most of us would want to read. Understanding that dry soil creates a barrier against water molecule penetration would tell us that the best defense against this would be to keep the soil's surface moist or wet the soil slowly over a period of time allowing for good penetration. Unfortunately many of us don't have the time to do either of these. Using a wetting agent mixed in our water will help to break the tension between the dry soil and water molecules allowing water to penetrate the soil more quickly. Wetting agents work well but let's not make our task of watering any more time consumming or expensive than it has to be.
As a collector of Japanese maples that are grown mostly in large pots it is important that they along with many other potted shrubs and trees are watered thoroughly, all potting medium moistened equally, throughout the containers. Keeping smaller pots watered well is normally no problem but larger pots that shrubs and trees require will need a little more care in keeping soil moisture consistant and equal throughtout a larger amount of soil. When potting larger plants and trees it works well to leave an inch or two of room in order to add a layer of mulch over the soil that will act as an insulator keeping the surface of the soil from drying out. I like to use a small size bark around the plant as this not only helps in insulating the soils surface moisture from evaporating too quickly, but also gives the potted plant or tree a nice finished look. Low growing ground covers with shallow rooting that won't compete for much of the plants moisture works well and looks really nice . Some ground covers that cascade over the sides of the pots can really add additional beauty to you planting. Some quality plastic or fiberglass pots I have found are manufactured with an inner and outer layer of material with an air space between the two layers. These double walled pots have worked really well in comparison with others in insulating the pots soil against warm drying temperatures. If the surface of soil is dry, a quick watering of the surface of the pots soil a day or a few hours prior to your more thorough watering helps greatly. This gives water time to break the barrier of dry soil allowing better penetration of your more thorough watering into the soil. Of course that wouldn't have to be done if the soil has been kept moist. Some plants require a drying of soil somewhat between waterings so this wetting of the soil prior to your more thorough watering works well. The following day or a few hours later when watering more thoroughly be sure to wet the top surface of soil equally around the pot until water drains from the bottom drain holes. Do not water the pot's soil surface in one location. Sometimes it is easier to stick the hose or watering can into one place around the plant than many places around a well filled pot of foliage, but this may not water all the soil equally. This is especially true when watering large pots with soils that are extremely well draining. Any water that drains from the pot before all the soil is moistened is wasted water.
Many fertilizer application instruction sheets note plants should be watered or soil should be moist before application of the product. Fertilizer manufacturers know that dry soils are a barrier, creating poor moisture penetration, that will not allow nutrients to easily penetrate into the soil. Plants need to be well hydrated with sufficient soil moisture. Without sufficient moisture penetrating the soil, before running out of the pot, very little water carrying nutrients can be absorbed by the plants root system.
Most plants need a well draining potting medium. A pooly draining soil, holding too much water, can cause root rot and fungal diseases that can kill or severly affect their health. Before any good watering practices can be implemented first check the soils ability to drain well and correct any poor draining conditions.
Potted plants can be a beautifull addition to gardens, patios, entries and other locations throughout our landscapes. It is no secret that potted plants normally take a little more care in keeping them healthy than those planted in the ground, but their useful versatility and beauty outweighs the little extra care.
