Container-grown tomatoes require regular watering since they don't benefit from the moisture found naturally within garden soils. Selecting a container the right size for your tomato plant helps prevent the soil from drying out too quickly, as a crowded pot has no room for moisture retention. Planting tomatoes in a 3- to 5-gallon pot and watering correctly ensures the plants get the moisture they need to produce an abundant crop.
Potting Soil and Moisture
The right type of soil in the container ensures the tomato plants have access to the proper amounts of moisture without suffering from overly dry or wet conditions. Soil-less potting amendments such as peat moss, vermiculite and perlite provide drainage to the soil mix so it doesn't become soggy. Compost and regular potting soil adds organic matter which absorbs moisture for the roots to access without clumping or becoming waterlogged. A mixture containing equal parts compost, peat and perlite helps maintain the right amount of moisture for the tomato roots.
The small confines inside the pot cause the soil to dry out more quickly. Drying is also sped up by hot weather and drying winds that evaporate the moisture from the soil at a higher rate. Watering frequency depends on the size of the plant and also on the weather conditions. Container-grown tomatoes usually need daily watering by the time they reach their mature size. During hot or dry weather the pots may need watered twice daily, in the morning and late afternoon. Check the soil every day and water when the top inch feels.
Pots require top watering, where the water is poured onto the soil at the base of the plant until the excess drains from the bottom of the pot. Watering until it begins to drain ensures the moisture penetrates to the entire soil and root zone of the tomato. Watering in the morning allows the moisture to fully penetrate and become absorbed by the soil before midday heat begins evaporating the moisture. If a second watering is necessary, doing so in late afternoon after the temperature begins to drop provides the same benefit.
Frequent watering washes nutrients from the soil, so most containerised tomatoes also need an application of soluble fertiliser every one to two weeks to replenish the nutrients. If the soil in the pots dries out quickly, the tomatoes may become drought-stressed. Stress leads to weaker, unproductive plants and may cause blossom-end rot. End rot causes the bottom of the tomato fruits to brown and rot. Applying a 2-inch layer of mulch on top of the soil in the pots helps prevent the soil from drying so that end rot doesn't affect your tomatoes.