When to fertilize tomato seedlings | + Best fertilizer choices

Tomato seedlings can be fertilized when you plant them out into garden beds or pots, during Spring and with fruit promoting fertilizer in Summer. Mix slow release organic fertilizer into the soil before planting out your seedlings and this will help to feed the soil bacteria and worms.

Tomato plants like a good balance of nutrients for them to grow well and produce lots of fruit. Check out this article for all you need to know about when to fertilize your tomato seedlings.

This article will explore how to prepare the soil and what to use to fertilize your tomatoes in Spring, Summer and when to use liquid fertilizer.

When to fertilize tomato seedlings

Here are the most important times to fertilize your tomato seedlings and the best fertilizer to use at each time.

Prepare the soil with fertilizer

Before planting out new tomato seedlings it is best to prepare the soil in garden beds with an organic fertilizer. I like to mix in aged cow manure which I a mild fertilizer and is high in carbon. It will add organic matter to the soil, improving its structure and increasing drainage.

Mix in a handful of pelleted chicken manure to give the deeper roots some long lasting nutrients. The pelleted chicken manure will slowly release over a few weeks feeding the tomato seedling and soil.

Check out organic fertilizers on Amazon below.

When you plant the seedlings

Add some extra slow release fertilizer on top of the soil when you plant out the tomato seedlings. I always use the pelleted chicken manure that I always have on hand. The one that I had bought recently is made for vegetables but any aged chicken manure will do.

This will be high in nitrogen and help with leaf and stem growth on newly planted tomato seedlings. Synthetic slow release fertilizers can also be used if you have them. Choose one made for vegetables as this will contain a range of macro and micronutrients to improve growth.

Fertilizing tomato seedlings in Spring

The next time you should give your tomatoes fertilizer is during the Spring growing season. This is when your tomato plant will be adding a lot of leaf and stem growth.

Giving them the fertilizer they need to get to full size before Summer hits will help the plant become strong enough to grow fruit.

Slow release organic fertilizer can be added every 4 weeks during Spring and watered in well. Add it onto the soil underneath the leaf canopy on the root zone. Water the plant well each time fertilizer is added. I always use pelleted chicken manure during Spring because it is mild and organic.

Fertilizing tomato seedlings in Summer

Once the Summer weather hits and the plant is established it is time to switch over to a fruit promoting fertilizer. Reducing the nitrogen to phosphorus to potassium ratio will stimulate the plant to grow flowers and set fruit.

Stop adding nitrogen rich fertilizer during summer and allow the plant to absorb and use up the nitrogen to adjust the balance in the soil. You may not need to add fruit promoting fertilizer at all if your plant is producing flower well.

For more fruit and flowers however a fertilizer higher in phosphorus will help this process. Look out for fertilizers labelled as fruit promoting as this will have a high phosphorus level.

Liquid fertilizer for tomatoes

Deciding when to use liquid fertilizer versus a slow release fertilizer can be tricky. Both are great for tomato plants but liquid fertilizer will be absorbed quicker. If you want your plant to get a quick nitrogen boost to help it to recover from sunburn or damage.

This works for promoting more fruit and flowers too. Giving your plant a boost of liquid phosphorus fertilizer will quickly change the N-P-K balance to help the plant to grow more tomatoes.

Liquid fertilizer can be added every 2 weeks if it is diluted correctly. My favorite liquid fertilizer for tomatoes is fish emulsion as it I natural, gentle and will help to feed soil bacteria and worms. I add this during Spring and stop in Summer because it is higher in nitrogen.

Slow release fertilizer for tomatoes

Slow release fertilizer for tomatoes is fantastic as it will last longer than liquid fertilizer. You will only need to add it at a maximum of every 4 weeks.

When to top dress tomatoes with compost

Tomatoes can be top dressed with compost half way through Spring or at the beginning of Summer to help to keep water in the soil. Rake back any mulch from around the plant base and add a 1 inch layer of compost.

This compost layer can then be topped with straw mulch to keep it moist. The nutrients from the compost will be washed down to the plant roots when it rains or when you water the plant.

When to fertilize tomato seedlings | Summary

Tomato seedlings can be fertilized every 4 weeks during spring and then given a dose of fruit promoting fertilizer at the start of Summer. Allowing the plant to use up the nitrogen in the soil to shift the balance in Summer will help to promote flower and tomato growth.

With too much nitrogen the plant will grow a lot of leaves but forget about growing fruit. This can be corrected with fruit promoting fertilizer high in phosphorus. Organic fertilizers are great as they are more forgiving. They are gentle on the soil and you will avoid adding too much of any one element.

Tomatoes are a great plant to start with when you begin vegetable gardening at home. They are one of the most rewarding plants and taste delicious when home grown.