5 Best Lilac Fertilizers | How and When to Apply

First referenced in the long-ago writings of Greek mythology, the intoxicating fragrance of lilacs (Syringa) has been enchanting observers for centuries. Both lilac trees and shrubs (different varieties) adorn many a formal and humble garden, contributing soft, abundant color and wafting perfume.

Lilac trees are one of twelve flowering, woody species that are closely related to olive trees. Although these can grow up to 25 ft. (7.6 m.) in height, from a biological standpoint, they’re still classified as bushes.

What we commonly recognize as a lilac bush really only differs from the ‘tree’ variety in its growing behavior. These can grow to between 4 and 12 ft. (2.4-3.7 m.) in height (depending on the variety) and are wide-spreading.

These ambrosial beauties are actually considered low maintenance, with some lilac varieties needing more seasonal pruning than others.

But, achieving optimal health, growth, color, and fragrance requires patience and an understanding of what lilacs need in order to thrive. This naturally includes the best lilac fertilizer.

Best Lilac Fertilizers

Espoma Organic Bone Meal 4-12-0

Best Lilac Fertilizer Granules

Espoma Organic Bone Meal 4-12-0

An organic, slow-release granular feed that is perfect for lilacs planted in nutrient-rich soil. The low nitrogen ratio means there is no risk of fertilizer burn and the high phosphorous content means an abundance of vibrantly colored lilac blooms.

 Miracle-Gro Bloom Booster Water Soluble Fertilizer 15-30-15

Best Water-Soluble Lilac Fertilizer

Miracle-Gro Bloom Booster Fertilizer 15-30-15

Either to provide your lilacs with a flying start at the beginning of the season or boost the health of a lackluster specimen, this water-soluble feed with a high phosphorous ratio will provide plenty of flowers all summer long.

Jobe's Azalea & Rhododendron Fertilizer Spikes 9-8-7       

Best Fertilizer Spikes

Jobe’s Fertilizer Spikes 9-8-7       

Convenient pre-measured fertilizer spike designed to be pushed an inch into the ground to provide a slow-release feed right through the growing season.

Choosing Fertilizer for Lilac Bushes

With over 1,000 different varieties, the one trait they all share, aside from beauty and fragrance, is their ease of care.

Lilacs prefer a nutrient-rich, well-draining environment with a neutral pH. They also require at least 6 full hours of sun in order to produce the bounty of blooms they’re known for.

Infertile soil, lilac fertilizer isn’t really necessary. But, when needed, an NPK that is low in nitrogen and higher in phosphorus will support their natural blooming process.

Amending your soil with well-aged compost will increase fertility as well as the lilac’s low-maintenance leanings.

Organic compounds, like bone meal and kelp, are effective alternatives to synthetic fertilizers that can provide adequate nutrients while increasing soil fertility over time.

Soil pH for Feeding Lilac

Soil pH determines a plant’s ability to absorb nutrients. Too high and nutrients get locked up in the soil, away from plant roots. Too low and the plant becomes vulnerable to pests and disease.

Lilacs thrive in a neutral pH range of 6.5 to 7.0. This supports optimal health and an unrestricted flow of vital nutrients.

It’s recommended that a soil test be done prior to planting new lilacs. If your pH is too high, amending the soil with compost will lower it, in the most beneficial way, over time. To raise it, an agricultural form of limestone is commonly used.

Lilac Bush N-P-K Ratio

Choosing the right NPK is easy when you understand what lilacs need. Every fertilizer label includes a three-numbered formula. This is the N-P-K ratio, indicating the product’s proportions of nitrogen, phosphorus, and potassium.

For example, a 5-10-10 NPK has 5% nitrogen, 10% phosphorus and 10% potassium. Every plant requires these three elements for optimal health. Just in different proportions or NPK ratios.

Lilac fertilizer needs to have phosphorus and potassium as a prerequisite. This will ensure vibrant foliage, a healthy root structure, a bounty of blooms, and protection against pests and diseases.

Nitrogen is also needed since foliage plays an integral role in the aesthetics of a lilac bush but to a lesser extent. A fertilizer that contains nothing but nitrogen, will result in lots of green foliage but very few blooms.

That said, if your soil is of poor quality and a soil test shows a deficiency in nitrogen or iron, then you’ll need to ramp up the nitrogen to compensate.

I’ve included an array of fertilizers with varying degrees of the 3 primary macronutrients to cover all bases.

Bone Meal for Lilac Trees

Granular bone meal, which is low in nitrogen, is a great soil additive for lilacs. Its multi-purpose perks include being slow-releasing (fewer applications), increasing soil pH, where needed, and offering a completely organic form of high phosphorus fertilizer. One that supports healthy bud formation and swaths of aromatic flowers.

Granules are easy to use, too. You would simply spread ½ cup, around the base of your tree or shrub, for every ½” of trunk diameter. Making sure to avoid applying within 3” of the trunk, itself. Instructions can vary between brands so be sure to read them prior to application.

Types of Fertilizer

There are four different fertilizer classes that offer flexible options for usage and gardening style.

  • Quick Release – liquid and water-soluble options offer an immediate uptake of nutrients. Resulting in accelerated improvement for ailing plants in poor soil.
  • Slow-Release – Heavily concentrated, granules and spikes offer a steady stream of nutrients over an extending period of time and are considered more eco-friendly.
  • Organic – made from natural compounds like well-rotted plant material and animal bi-products that contain beneficial levels of nitrogen, phosphorus and potassium.
  • Inorganic – manufactured with minerals and chemicals, these can result in a higher yield. But, can also potentially contaminate soil and nearby water sources.

Fertilizer Granules

Granules are slow-releasing and can provide consistent nourishment for up to nine months (depending on the brand). With the first results often showing in just a couple of weeks. They’re also less likely to cause root burn and are considered easier on the environment.

Granules are applied by casting them evenly around the base trees, shrubs, and plants. No watering is needed to activate and is less likely to leach into nearby surface or groundwater.

Fertilizer Spike

Spikes are one of the most convenient to use, especially if you grow lilacs in containers. Pre-measured in various sizes, they’re easy to push into loamy soil.  And being slow-releasing, they run little risk of root burn.

Nutrients are released from these by micro-organisms that naturally live in the soil. And carry the added benefit of stimulating an increased resistance to disease and pests. Unused spikes can then be stored mess-free until needed.

Liquid Fertilizer

Most liquid fertilizers are used by applying a water-diluted mixture around the base of your plants. Some are formulated to also be used as a foliar spray. Nutrients are then carried immediately to the roots through the soil or leaves.

Liquid feeds tend to keep the pH levels in your soil balanced, as well. And are usually quite economical. However, caution is recommended, as over-feeding is common and could lead to root burn.

Synthetic Vs Organic

Deciding between an organic and synthetic option is simply a matter of preference and end-result expectation. However, a basic understanding of how each works and affects your environment will support an informed decision.

Organics are typically plant or animal-based while inorganics are mass-produced using minerals and synthetic chemicals.

Organic feeds naturally contain lower levels of nutrients but can nourish your lilacs for longer periods of time. This option can also improve the surrounding soil.

The use of inorganic feeds can result in a larger bloom count. But, they can also potentially contaminate your soil, over time.

5 Best Lilac Fertilizers

Lilacs typically grow best in regions with cool summers and mild winters. But, with a little resourcefulness and the right fertilizer, they can prosper in other hardiness zones, too.

I’ve tested a number of fertilizer options on my own lilac collection, and I’ve compiled a list of the top 5 performers, based on results and ease of use. Including product details and the pros and cons allows for an informed decision. 

1. Espoma Organic Bone Meal 4-12-0

Best Organic Lilac Fertilizer

Espoma Organic Bone Meal 4 12 0

Pros      

  • All natural source of organic phosphorus and nitrogen
  • Helps to loosen heavy, clay soil

Cons

  • Not recommended for plants that require higher potassium

This organic bone meal from Espoma is spot on for use when you have the perfect soil conditions for lilacs. It will help to keep nutrient levels as the season progresses and its slow-release formula means it only needs to be applied once at the start of the growing season and then once more 8 to 12 weeks later.

The outcome will be lilac bushes with plentiful blooms thanks to the naturally occurring high phosphorus that bone meal provides. In addition, there is just enough nitrogen to support healthy foliage growth. 

It’s an option that can always be found under my potting bench. In spring, when tilling my soil, I’ll add fresh compost and then an appropriate dose of this around all of my flowering perennials and also where I know I’m going to be planting tomatoes and squash.

How To Use: Apply 1 or 2 pounds depending upon the size of the shrub or tree. Apply 2 oz or one heaping tablespoon per potted plant and work into the soil.

Pros      

  • Plentiful buds in just a few days
  • Easy to use and store

Cons

  • Multiple boxes may be needed for larger gardens

No complete comparison is without Miracle-Gro and this is my top pick for getting your lilacs off to the best start possible at the start of the growing season and then every time they need an instant boost of nutrients thereafter.

The high-phosphorus NPK and water-soluble formula practically guaranteed abundant blooms by stimulating enzymes that trigger bountiful bud production on my potted lilac trees.

One box covers around 600 sq ft, so I only needed one for the whole season. I found this very easy to mix and apply and based on the number of blooms I got; this has great value for money.

How To Use: In a watering can or hose attachment, mix 1 tablespoon of Miracle-Gro per one gallon of water. Then, soak the base of your plants every 7-14 days.

Pros      

  • Optimal Nutrition For Bud Production And Green Foliage
  • Releases nutrients gradually for up to 4 months

Cons

  • May be too strong for lilacs planted in nutrient-rich soil

When starting out in a new garden, where the soil may need help in the fertility department, this triple 20 feed from Jack’s Classic will help to increase that and provide new plantings with a nutrient-balanced growing environment.

With equal parts nitrogen, phosphorus, and potassium, this can be successfully used to fertilize just about any kind of plant growing in less-than-desirable soil.

How To Use: For trees and shrubs, apply 1 tablespoon per gallon of water used. Repeat every 10-14 days. For annuals, perennials, vegetables, and roses, 1 tablespoon per gallon is applied every 7-10 days.

Pros      

  • Lasts up to 8 weeks
  • Convenient resealable bag

Cons

  • May break off in dry soil 

Jobe’s spikes are one of the easiest ways to fertilize large plants and shrubs. Since this is formulated for acid-lovers, this is the perfect choice to fertilize your lilacs and raise your soil pH, if needed. These fertilized my climbing lilacs for months at a time, while I was off doing other things.

I then came home to climbers with larger, more colorful blooms and leaves! I suggest watering prior to application as breaking can occur in dry soil.

How To Use:  Insert the recommended number of spikes (per plant size) around shrubs and the slow-release formula will feed them for up to 8 weeks.

Pros

  • Beneficial NPK for well-composted soil
  • Fast growth in just one season

Cons

  • Not recommended for potted trees and shrubs

This slow-releasing, granular option worked really well on an oversized, white lilac that I have growing in an area where the soil isn’t as fertile. The higher nitrogen helped to improve that without me having to worry about root burn.

The higher ratio of phosphorus and potassium focused on increasing the number of blooms is a great choice fertilizer for Dogwoods and hydrangeas too. It’s a versatile win-win!

How To Use: Spread 1 cup for every sq ft of the growing area within the drip line. Then, work granules into the top 3” of soil and water thoroughly for a 2-month feeding.

Do Lilacs Need Fertilizing to Bloom

When grown in a consistently fertile growing medium, lilacs will get all the nutrients they need from the soil and will absorb them as they need them. There will be no need for extra fertilization.

But, of course, not all soil is created equal. If your lilacs are growing in less-than-fertile ground soil, supplementing nutrients with the right fertilizer can increase your chances for vibrant foliage and lots of blooms.

If you’re growing lilac trees or shrubs in pots, the inevitable leaching of soil and nutrients will make the need to supplement nutrients a must.

In these scenarios, remember to choose low nitrogen, high phosphorus feed to encourage blooms without forcing foliage growth.

When planting new lilac plants in poor soil, a well-balanced feed will encourage vibrant foliage growth, healthy root establishment, better nutrient and water uptake, and abundant flower production.

How to Fertilize Lilac Trees

How to fertilizer your lilacs will depend on the application method you choose. Liquids, diluted with the recommended amount of water, are applied using a watering can, for small areas, or a hose attachment, for larger garden spaces.

Apply these in the cooler hours of the day, so as not to scorch those lovely leaves and blossoms in direct sun.

Dry granules and spikes can be applied any time of day and don’t necessarily require watering in. But, applying them just before a forecasted rainfall will hasten activation.

Diluting water-soluble granules and applying the resulting ‘tea’ can give you more control over the amount and frequency of feeding. Like liquid concentrates, this option also gives you a more immediate result.

However, before any fertilizer is applied, a soil test should be done to see if your lilacs need fertilizing, at all.

How Often to Feed Lilac

How often to fertilize will also be dictated by the brand and application method you choose. Different brands recommend different usage frequencies based on their specific formulation.

For example, Jobe’s spikes need re-applying every 8 weeks, which is roughly two or three times per growing season. Scott’s granules suggest the same.

Water-soluble granules, like my pick from Jack’s Classic, should be applied every two weeks for consistent nourishment. As should MiracleGro’s BloomBooster formula.

Again, when using liquid fertilizers for potted plants, the frequency of application could be even higher. This would be based on leaching and plant respiration in warmer climates.

Regardless of which brand you choose, label directions should always be followed to ensure that no damage is caused by accidental over-fertilizing.

Signs of Fertilizer Burn

No one intentionally over-fertilizes their lilacs, but on occasion, it does accidentally happen. Signs of over-fertilizing include:

  • Yellowing leaves
  • Foliage wilting
  • Browning edges on leaves and flowers

A clear sign of nitrogen overuse will appear as excessive amounts of foliage and few to no flowers. Too much phosphorus will cause the opposite.

Signs of root burn, in particular, include stunted growth, a wilting of stalks and new branches, as well as foliage, no new flowers, and in extreme cases, the death of the plant.

If over-fertilizing happens with ground planted lilacs, simply cut back the damaged bits and stop fertilizing. In pots, do the same, followed by flushing the soil with water only, without overdoing it.

When to Fertilize Lilac

When planted in fertile soil, new lilac plants will not need fertilizing until after the first or second year. Whether they need fertilizing, at all, will depend on how well the roots have been established and how healthy they are.

When planting in poor soil, a triple 20 fertilizer, in spring, before new growth appears, will create a well-balanced growing environment.

For young or long-established lilacs that need a nutrients boost, begin your fertilizing regimen in spring, following the manufacturer’s instructions. Then, continue until around mid-July.

Stopping at this point will contribute to winter survival in colder climates. But, also slow new growth that may be vulnerable to an early autumn frost.

Best Lilac Fertilizers Verdict

Choosing the best fertilizer for your lilac tree or bush is easy when you know what you’re looking for. Just keep in mind that they are not heavy feeders and don’t need fertilizing until they are fully established.

As far as N-P-K is concerned they need a higher ratio of phosphorous to support the development and growth of buds and plenty of blooms and a simple soil test will determine how much nitrogen and potassium are required.

So, based on your newfound knowledge you should select Espoma Organic Bone Meal for use on lilacs in already nutrient-rich soil. Or, where an instant boost of nutrients is required, opt for Miracle-Gro Bloom Booster.

Either to provide your lilacs with a flying start at the beginning of the season or boost the health of a lackluster specimen, this water-soluble feed with a high phosphorous ratio will provide plenty of flowers all summer long.

Espoma Organic Bone Meal 4-12-0

Best Lilac Fertilizer Granules

Espoma Organic Bone Meal 4-12-0

An organic, slow-release granular feed that is perfect for lilacs planted in nutrient-rich soil. The low nitrogen ratio means there is no risk of fertilizer burn and the high phosphorous content means an abundance of vibrantly colored lilac blooms.

 Miracle-Gro Bloom Booster Water Soluble Fertilizer 15-30-15

Best Water-Soluble Lilac Fertilizer

Miracle-Gro Bloom Booster Water Soluble Fertilizer 15-30-15

Either to provide your lilacs with a flying start at the beginning of the season or boost the health of a lackluster specimen, this water-soluble feed with a high phosphorous ratio will provide plenty of flowers all summer long.

FAQ’s Lilac Fertilizer