How to Choose the Right Fertiliser for Flowering Plants

Flowers bring beauty and fragrance to your garden. Whether you grow annuals, perennials, bulbs, roses, or ornamental grasses, proper fertilisation is key to promoting healthy growth and blooming. With numerous flower fertiliser options available—ranging from synthetic to organic—it’s important to understand how to meet your plants’ specific needs.

Understanding fertiliser types

Complete Fertilisers

A complete fertiliser provides nitrogen (N), phosphorus (P), and potassium (K), essential nutrients for plant growth. Nitrogen promotes lush foliage, phosphorus stimulates blooming, and potassium develops strong roots. These nutrients appear in a fixed order (N-P-K) on fertiliser packaging. For example, a 10-10-10 fertiliser contains 10% of each nutrient, while a 10-30-20 fertiliser has a higher phosphorus content, ideal for flower growth. Choose fertilisers with a higher phosphorus ratio to encourage blooming.

Organic vs. chemical fertilisers

Organic fertilisers, derived from natural sources like compost, fish emulsion, or bone meal, improve soil quality while nourishing plants. They are less likely to burn plants and promote long-term soil health. However, they work slowly and can be more expensive. In contrast, chemical fertilisers are synthetic and act quickly. They are convenient but may damage plants if overapplied and do not enhance soil structure.

Simple and slow-release fertilisers

Simple fertilisers contain just one nutrient, such as nitrogen, phosphorus, or potassium, to address specific soil deficiencies. Slow-release fertilisers, often coated to control nutrient release over time, are ideal for gardeners who prefer infrequent fertilisation. Organic fertilisers are naturally slow-release, as nutrients break down gradually.

Foliar Fertilisers

Foliar fertilisers are sprayed directly onto plant leaves, allowing for quick nutrient absorption. While they can quickly address deficiencies (such as iron or potassium), foliar feeding alone is insufficient for overall plant health.

Suggested fertiliser practices for flowers

Annuals, perennials, bulbs, roses, ornamental grasses, and wildflowers

To keep flowering plants healthy, fertiliser should be chosen based on soil tests and plant types. Synthetic or organic options are both effective if applied correctly. Fertiliser grades on packaging refer to the percentage of nitrogen, phosphorus, and potassium (N-P-K). A balance of these nutrients is crucial for flowering plants, with phosphorus being key to promoting blossoms.

Soil pH and Amendments

Flowering plants thrive in soils with a pH range of 5.5 to 7.0. To raise pH, use limestone; to lower it, apply sulphur. For optimal results, mix limestone or sulphur into the top 6–8 inches of soil. It may take several months for the pH to stabilise, but a balanced pH ensures that nutrients are easily accessible to plants.

How and When to Apply Fertiliser

Annuals, perennials, and bulbs

• Annuals: Apply fertiliser during bed preparation, then reapply 6–8 weeks later. Flowers blooming into fall may need a third application in late August.
• Perennials and Ornamental Grasses (new plantings): Fertilise during bed preparation, then again after 6-8 weeks.
• Established perennials and ornamental grasses: fertilise when spring growth begins. Apply again 6–8 weeks later if needed.
• Spring Bulbs: Fertilise as new growth emerges in spring and again in late summer.
• Summer Bulbs: Fertilise at planting, then after flowering for plants with short blooms. For long-blooming bulbs like dahlias, fertilise again in mid-July.

Roses and Wildflowers

• Roses: Apply fertiliser in May, June, and July, but stop after mid-July to avoid late-season growth that could be damaged by frost.
• Wildflowers: Wildflowers typically need fewer nutrients. A single fertiliser application in spring is usually sufficient.

Fertiliser Application Tips

When fertilising, be sure to pull back mulch to apply nutrients directly to the soil. Fertiliser should be worked into the top 4-6 inches of soil for new beds or scratched into the surface for established plantings. Water thoroughly after fertilising to help nutrients reach plant roots.

Natural and organic fertiliser equivalents

For gardeners using organic fertilisers, it’s important to adjust application rates based on nutrient content. For example:

• 1 lb. of nitrogen can be supplied by 8.3 lbs. of blood meal.
• 1 lb. of phosphate comes from 6.75 lbs. of bone meal.
• 1 lb. of potash can be supplied by 25 lbs. of kelp meal.

Keep in mind that nutrition analysis can vary by producer, so adjust quantities as needed.