Low-Nitrogen Fertilizer: When To Use & Why (Full Guide)

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Although nitrogen is a necessary macronutrient for the growth and development of plant cells, there may be instances where a fertilizer with low nitrogen levels is required.

Too much nitrogen in the soil could either damage the plant or have undesired side effects such as sudden growth spurts or more leaves but fewer flowers. 

A low-nitrogen fertilizer is a fertilizer that contains a higher content of potassium and phosphorus but a small content of nitrogen. This type of fertilizer is suitable for flowering and fruiting plants, especially around bloom time. Many organic fertilizers contain a low percentage of nitrogen.

A low-nitrogen fertilizer serves a specific purpose, but you should know when exactly you should use it, which of the commercial options are best, and which types of natural fertilizer have less nitrogen than the others.

Low Nitrogen Fertilizer

When you buy a bag of fertilizer, you’ll often find three numbers on it such as 5-5-5 or 10-10-10. These numbers refer to the content of nitrogen (N), phosphorus (P), and potassium (K) in the fertilizer respectively.

A low-nitrogen fertilizer will have a label such as 5-10-10, 3-12-12, or something similar with the first number being lower than the other two.

When growing flowering plants where the blooms are more important than the leaves, then you’d want to apply a low-nitrogen fertilizer that is also high in phosphorus. 

Nutrients in Fertilizer

Most fertilizers contain both macronutrients and micronutrients. Macronutrients are the three main nutrients, nitrogen, phosphorus, and potassium that most plants can’t do without.

Micronutrients refer to other minerals that plants need in trace amounts. These include iron, boron, magnesium, calcium, zinc, manganese, and copper among others.

The fertilizer you buy will usually list the nutrients contained in the fertilizer and the percentage of those nutrients to help you apply the right amount of fertilizer to the plants.

Role of Nitrogen in Plants

Nitrogen is critical to plant growth, but most plants do not require large amounts administered through fertilizer. However, a lack of nitrogen can be detrimental to plant health.

What Does Nitrogen Do for Plants?

Most plants need nitrogen in the soil to develop a full root system, grow stems, and have lush green leaves.

The richer the soil is in nitrogen, the healthier your plants will be and the faster they’ll grow. Nitrogen deficiency can lead to stunted growth and sickly plants.

Does Nitrogen Increase Leaf Growth?

If you want to have full foliage with lush green leaves, then apply a high-nitrogen fertilizer; however, this often comes at the cost of flowering. So the decision to add extra nitrogen really depends on your goals.

Want full, lush, bushy plants? Increase the nitrogen.

Want bountiful blossoms for a big harvest later? Go with a low-nitrogen fertilizer.

How Much Nitrogen Do Plants Need?

The amount of nitrogen needed depends on the plants themselves and the growth stage they’re going through.

Young plants need more nitrogen in the soil to develop their roots, stems, and leaves. During the bloom season, the plants will need less nitrogen and more phosphorus.

What Does Too Much Nitrogen Do to Plants?

Too much nitrogen is not good for plants. It can cause fertilizer burn that damages the roots of the plants.

It can also stress out the plant with a sudden growth spurt that causes shock and disrupts the growth stage of the plant. 

What Plants Need High Nitrogen?

Leafy green plants such as spinach, kale, lettuce, bok choy, Brussels sprouts, and mustards all need a high dose of nitrogen in the soil to support the growth of these green leaves.

Lawn grass of all types needs a lot of nitrogen in the fertilizer.

What Is a Good Nitrogen Level in Soil?

Normal soil should have 40 ppm of nitrogen before planting new crops. This is usually enough to give the plants a good start.

Some plants, such as beans, are nitrogen fixers and don’t need very much nitrogen to grow well.

How Do You Know if a Plant Needs Nitrogen?

Nitrogen deficiency is easy to spot in many plants. Usually, the plants will stop growing, the leaves will turn yellow, and new leaves will be smaller than normal.

The plant will have stunted growth, and the stems will be soft and withered. 

Role of Phosphorus in Plants

Phosphorus given to plants encourages more flower buds and larger blooms. It also promotes winter hardiness in plants to keep them from freezing.

Phosphorus also improves water absorption by the roots and promotes better water efficiency.

Role of Potassium in Plants

Potassium is responsible for moving the moisture and nutrients inside the plant’s tissues. It also triggers the enzymes responsible for the production of starch and protein along with other plant building blocks.

0-10-10 Fertilizer

This type of fertilizer contains zero nitrogen. If you have flowering plants, then most likely this is the type of fertilizer to apply just before the first flower buds have emerged. You’ll get larger blooms and richer colors with this fertilizer.

When To Use a Low-Nitrogen Fertilizer

If you have plants that produce flowers and fruits, then you’ll need to switch to a low-nitrogen fertilizer during the flowering season to increase the yield.

Too much nitrogen in the soil leads to more leaves and stems and fewer flowers and fruits. 

You should also use low-nitrogen fertilizers with veggies to increase the number of antioxidants in those vegetables. The same goes for herbs.

Too much nitrogen in the soil can decrease the flavors and medicinal properties of these herbs and makes them leggy, so it’s recommended to apply low-nitrogen fertilizers. 

Low-Nitrogen Fertilizer Options

While there are many low-nitrogen fertilizers commercially available, such as the popular bloom boosters, there are also organic, natural options that you can utilize instead.

1. Lilly Miller Bulb & Bloom Food

Lilly Miller Bulb & Bloom Food 4-10-10, 4lbs

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This low-nitrogen fertilizer is perfectly suited for flowering plants. It has a 4-10-10 formula with more phosphorus and potassium than nitrogen. It promotes larger flowers with richer colors and fragrances.

2. Liquinox 0-10-10 Bloom

Liquinox 0-10-10 Bloom, 1 quart

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This fertilizer contains zero amounts of nitrogen but a full dose of phosphorus and potassium. It should be applied right before the flowering season to increase vegetable and fruit harvests.

3. Aged Manure

Aged manure has less nitrogen than fresh manure, and it won’t burn your plants’ roots.

If you want aged manure with really low nitrogen, choose cow manure. It has 1-2 percent of nitrogen on average per weight.

4. Compost

If you make your own compost at home, then you can adjust the materials you add to the compost pile to decrease the amount of nitrogen in the end product.

Try increasing the dry plant materials in the pile to get phosphorus- and potassium-rich compost with less nitrogen.

5. Bone Meal

Bone meal contains more calcium and phosphorus than potassium or nitrogen. It’s a natural way to enrich the soil and feed phosphorus-hungry plants such as flowers without adding too much nitrogen into the mix.

6. Kelp Meal

Kelp meal is rich in phosphorus, plant hormones, and other micronutrients but has little to no nitrogen. It releases its nutrients slowly to feed the plants for weeks.

7. Wood Ashes

When wood is burned, carbon is stripped from the remaining ashes. This leaves an organic material with relatively low nitrogen.

Mixing the ashes with the soil will improve the texture and aeration without adding nitrogen.

8. Lime

Ground limestone is high in calcium but low in nitrogen.

Adding it to the soil makes the soil more alkaline, improves water retention, adds calcium carbonate and magnesium carbonate, and may help keep pests away from the plants.

9. Iron Chelate

This fertilizer is rich in iron and can be added to alkaline soil to improve its pH. Plants that suffer from iron deficiency will benefit from this iron salt.

10. Epsom Salt

This is a form of magnesium sulfate and can be used to treat soil poor in either magnesium or sulfur. Use it with your flowering plants to have larger blooms with richer colors.

11. Cal-Mag 

This is wonderful low-nitrogen fertilizer that contains both calcium and magnesium. It’s a great blend for flowering plants.

12. Potash

If the soil is deficient in potassium, then adding potash will treat this deficiency. Potash is also an ideal fertilizer when growing vegetables in your garden. 

Closing Thoughts

Not all plants need a high dose of nitrogen in the soil. For those plants, a low-nitrogen fertilizer is all they need to grow and thrive.

There are many commercial options on the market, or you can try natural fertilizers like kelp meal, lime, and wood ashes among others.