How to Grow Tomatoes: Your Complete Guide

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Feeding tomatoes can be a tricky subject, particularly for beginner gardeners. When do you feed? What do you feed with? And when should you stop?

This is just a small selection of your possible questions, so let me help you with my simple guide to all things tomato feeding.

Feeding Tomato Plants: The Basics
Types of Fertilisers
Several types of fertilisers are suitable for tomato plants, each with its own characteristics and benefits.

The three major nutrients that tomato plants require are nitrogen, phosphorus, and potassium. When selecting a fertilizer, look for one that provides these key nutrients, often labelled as N-P-K on the packaging.

Organic fertilisers: These fertilisers are derived from natural sources. Organic fertilisers release nutrients slowly, providing a steady food supply for your tomato plants. These fertilisers also contribute to long-term soil health.
Inorganic fertilisers: Also known as chemical or synthetic fertilisers, inorganic options provide nutrients rapidly and can be tailored specifically for tomatoes with particular N-P-K ratios. Examples include granular slow-release fertilisers and water-soluble fertilisers.

Soil Amendments: These are feeds you add to the soil rather than directly to the plant. Think of things such as manure, fish blood & bone, chicken pellets and compost.
Feed bags: A feed bag is simply a tomato grow bag that already has a slow release fertiliser in it and shouldn’t need any more feeding.
Inorganic fertilisers will always be stronger, and at first, you will always see better results. The nutrients are easily accessible by the plants, and they take them straight up. But I still use organic fertilisers.

Organic fertilisers help improve your soil over time, and allow you to grow organic tomatoes.

There is always a trade-off, they are usually more expensive (even if the bottle is the same price, you probably need to use double the dose of organic fertiliser), but you get healthy soil which improves year over year and a lovely organic crop.

Whether to buy organic or not all comes down to whether you want to eat organic tomatoes or not.

Timing and Frequency
You want to start feeding your tomatoes before you even plant them, you do this by feeding the soil and ensuring they are going into a nice healthy soil.

This can be achieved by adding compost, well-rotted manure, chicken manure or fish blood & bone to your soil.

Homemade fertilisers are also brilliant at improving your overall soil health. I personally love making compost tea and using that, but nettle and comfrey feeds are other popular alternatives.

When to start applying liquid feeds
The common wisdom is to apply your liquid tomato feed once the first flowers appear.

You want to avoid feeding with nitrogen-heavy feeds as these promote leafy green growth rather than fruit production.

What I Do
My usual routine is this:

Apply a compost mulch to the soil a few weeks before planting.
Feed this soil with a single application of compost tea.
Plant my tomatoes and don’t feed them at all until the first flowers appear.
Begin feeding with an organic tomato feed.
How To Apply Liquid Feed
Liquid tomato feeds are very simple to use.

You simply dilute the feed with water, usually in a watering can, and then water the base of the plant.

The dilution rates vary with every fertiliser, so read the packaging properly.

Also, the feeding frequency changes with different fertilisers, so again, read the bottle!

When To Stop Feeding Tomatoes
Feeding tomatoes can help you get a much larger harvest, but when is the time to stop feeding your tomato plants? And can you hurt them by overfeeding?

So when to stop? I usually stop when the last truss of tomatoes has started developing.

If you are using grow bags to grow your tomatoes, then maybe stop a couple of weeks earlier. As I grow mine in beds in my greenhouse, then I know that the goodness from the feed won’t be wasted either way.

As soon as the tomatoes are out, something else will be going in the same bed.

Why stop?
The only real reason to stop feeding your tomatoes is that it becomes a waste of money.

I would say that this point is probably reached a week or two after all of the tomatoes are set on your plant.

Past this point, you are probably not gaining too much from feeding your plants. You are better saving any left over feed for next year’s crop or giving it to something else that is still producing.

Cutting down your feeding times or using half doses is an excellent way to save some food but also still help your tomato plants along.

Common Feeding Concerns and Solutions
Over-Fertilisation
Over-fertilisation can cause significant problems for tomato plants, leading to excessive foliage growth, unhealthy fruit, and reduced yields. The symptoms of over-fertilisation may include:

Dark green and curled leaves: When tomato plants receive too much fertiliser, especially nitrogen, they develop dark green, curled leaves.
Reduced fruit production: Excessive fertilisation can cause tomato plants to focus more on foliage growth, producing fewer fruits.
Unripe fruits: Over-fertilised tomato plants may struggle to ripen their fruits, leaving them hard and green.
Nutrient Deficiencies
Tomato plants require a balanced mix of nutrients to grow healthily. Some common nutrient deficiencies in tomato plants are:

Calcium deficiency: A lack of calcium can cause blossom end rot, where black sunken areas appear on the fruit’s blossom end. This issue is also exacerbated by uneven watering and root damage.
Magnesium deficiency: Insufficient magnesium levels can result in yellowing leaves, starting from the edges and moving towards the centre.
Potassium deficiency: A potassium deficiency can cause the tomato leaves to develop a yellow or brownish colour between the veins, leading to wilting and reduced fruit development.
Frequently Asked Questions
When to start feeding tomatoes?
The common wisdom is to apply your liquid tomato feed once the first flowers appear.

You want to avoid feeding with nitrogen-heavy feeds as these promote leafy green growth rather than fruit production.

Best feed for tomato plants?
You want a feed with a high potassium content as this is what promotes the development of flowers and fruit. I am currently running a trial testing 8 different tomato feeds, so sign up for my newsletter to find out the results of that!

Home fertiliser for tomatoes?
Nettle and comfrey teas make good tomato feeds. You can also make your own seaweed feed.

Feeding tomatoes in pots?
Feeding tomato plants in pots requires a slightly different approach, as the nutrients in the potting mix can be depleted more quickly.

You might need to feed them a little more regularly than the packaging says, but apart from that, there isn’t too much difference.