Tomatoes are heavy feeders that require consistent input to produce a high yield of quality fruit. Successful growth depends on preparing the soil and continuing with strategic, ongoing nutrient applications throughout the season. Understanding what to put on your tomato plants and when to apply it involves a staged approach that supports the plant from root development to fruit ripening. Providing the right amendments and nutrients at the correct times ensures your plants remain healthy, robust, and capable of delivering a plentiful harvest.
Building the Foundation: Essential Soil Amendments
The structure and chemistry of the soil are the starting point for healthy tomato growth, requiring deep preparation before planting begins. Tomatoes thrive in loose, rich soil with excellent drainage that still retains adequate moisture. Incorporating high-quality organic matter, such as well-aged compost or composted manure, significantly improves soil structure by adding humus and increasing porosity. This helps roots spread quickly and efficiently.
It is helpful to conduct a soil test to determine the existing pH level and nutrient profile before adding any amendments. Tomatoes absorb nutrients most effectively when the soil pH is in the slightly acidic to neutral range, ideally between 6.5 and 7.0. If the soil is too acidic (below 6.0), you can raise the pH by mixing in ground limestone. If it is too alkaline (above 7.0), elemental sulfur or composted pine bark can be used to lower the number. Peat moss or coir can also be worked into heavy clay soils to further improve aeration and drainage, preventing the soggy conditions that tomatoes dislike.
Primary Feeding Strategy: Selecting and Applying Fertilizers
Routine nutrient inputs are necessary throughout the growing season to match the tomato plant’s high demand for nitrogen (N), phosphorus (P), and potassium (K). These macronutrients, represented by the NPK ratio on fertilizer labels, must be balanced and adjusted based on the plant’s current stage of development. Nitrogen promotes vegetative growth, phosphorus supports root development and flowering, and potassium enhances fruit quality and size.
In the initial vegetative growth phase (about 4 to 6 weeks after transplanting), the focus is on building a strong scaffold of leaves and stems. A balanced fertilizer, such as a 19-19-19 or a formula with a slightly higher nitrogen component, supports foliar and canopy formation. Once the plant begins to bud and flower, the nutritional strategy shifts to encourage fruit set and development. Switching to a formula with proportionally higher phosphorus and potassium (e.g., a 5-10-10 or a 6-8-12 ratio) signals the plant to invest energy into reproduction rather than excessive leaf production.
The method of application depends on the type of fertilizer chosen, with options including granular and water-soluble forms. Granular, slow-release fertilizers can be worked into the soil as a side-dressing every three to four weeks, providing a consistent nutrient supply. Water-soluble fertilizers, which are diluted and applied with water, offer more immediate uptake and are often used for weekly feeding during the peak fruiting period. Applying these routine feeds a few inches away from the stem and watering them in ensures the nutrients reach the active root zone without burning the plant’s base.
Targeted Treatments for Common Nutrient Deficiencies
Beyond the routine NPK feeding, tomatoes frequently require targeted inputs to correct or prevent specific mineral deficiencies that can hinder fruit development. The most common issue is Blossom End Rot (BER), which appears as a dark, sunken spot on the bottom of the developing fruit. This condition is caused by the plant’s inability to efficiently move calcium to the rapidly growing fruit, not necessarily a lack of calcium in the soil.
To correct BER, applying a calcium source, such as commercial calcium sprays or calcium nitrate, delivers the nutrient directly to the plant tissues. Incorporating bone meal or dolomitic limestone into the planting hole can also provide a slow-release calcium source to help prevent BER from the start.
Addressing Magnesium Deficiency
Another common need is magnesium, which plays a role in chlorophyll production and overall foliage health. Magnesium deficiency appears as yellowing between the leaf veins, starting with older leaves. A quick and effective treatment is an application of Epsom salts (magnesium sulfate) as a foliar spray or a soil drench. Corrective treatments like foliar sprays work quickly because they bypass the soil, allowing the plant to absorb the needed mineral directly through its leaves.
Protecting the plant from pests and diseases is another form of targeted input that ensures continuous, healthy growth. Specific treatments like neem oil or insecticidal soap are applied directly to the foliage to control insect populations that damage leaves and stems. These applications protect the plant’s existing structure, allowing it to focus resources on fruit production instead of recovery.
The Role of Mulch in Maintaining Growth
Applying a layer of mulch to the soil surface is a simple, yet highly effective, input that stabilizes the environment for the tomato plant. Organic mulches like straw, shredded leaves, or grass clippings help to maintain consistent soil moisture by significantly reducing water evaporation from the surface. This moisture retention is important for tomatoes, as inconsistent watering can trigger issues like Blossom End Rot, even when calcium is present.
The mulch layer also acts as an insulator, moderating soil temperature by keeping the root zone cooler during hot summer months. A two-to-three-inch layer of mulch suppresses weed growth, eliminating competition for applied water and nutrients. The barrier created by the mulch prevents soil-borne disease pathogens from splashing up onto the lower foliage during watering or rain, which helps to maintain the plant’s overall health.