Tomato Fertilizer


Hi. Looking for advice regarding fertilizing Tomatoes. The plants were grown by seed, potted up and then potted into cloth bags using store bought soil. They are looking good. They live in a backyard city greenhouse where previous crops have done very well without much fertilizer. There are four varieties, most have started to flower.

Should we now give them a high phosphorus fertilizer or a 20-20-20? The only fertilizer that they have received so far are a few rounds of micro-seaweed, Marphyl and not a strong mixture. Looking for advice. Would love the best yield, however, concerned about over fertilizing.

We also have pea, carrots, cucumbers, beans, lettuce, beets. All in containers. Should we fertilize them?

Also, do you recommend a specific brand?




Thank you for contacting Toronto Master Gardeners.

Feed your container-grown vegetables because frequent watering will leach the nutrients out of the growing medium. Use an organic fish or seaweed-based, or balanced (e.g. 10-10-10 N:P:K) soluble fertilizer every two weeks. Top dress with compost once a month.

Carrots and parsnips don’t need much and should only receive the compost. Radishes do not need to be fed.

Choose a fertilizer that’s higher in phosphorous for plants that produce flowers, fruits (like tomatoes and cucumbers), or edible roots.

Tomatoes are heavy feeders – feed regularly when planted, when flowers begin to form and when fruit begins to form.

As noted above, we recommend a fertilizer that is higher in phosphorus for plants that produce fruit such as tomatoes because phosphorus is a nutrient that is important in seed and flower formation. Specialty tomato fertilizers are formulated as such.

Switching to such a formula now should result in higher fruit production.

Toronto Master Gardeners is unable to give specific product or product provider recommendations.