11 Perennials You Should Feed in March for Better Blooms

The difference is usually happening below the surface.

As the days draw out and the soil begins to warm, perennial roots kick-start a fresh season of growth. March offers a short, valuable window: feed a few key plants at the right moment and an ordinary border can become a long-running firework show. Miss that opportunity and you may spend the rest of the year asking yourself why your neighbours’ gardens seem to outshine yours.

Why March feeding makes or breaks perennial displays

By March the ground has typically thawed, air returns to the soil and roots spring back into action quickly. In this brief period they are both active and hungry, ready to take up nutrients with remarkable efficiency.

"Feeding perennials in March gives them fuel precisely when they restart growth, shaping both the strength of stems and the abundance of flowers."

Right now, plants are repairing what winter has depleted: they’re rebuilding root networks, replenishing stored energy and pushing new shoots. A gentle, consistent supply of nutrients supports all three jobs without forcing soft, sappy growth that collapses the moment a windy day arrives.

This is where organic fertilisers and slow-release feeds earn their keep. Put down in late February, March or very early April, they release gradually over three to six months. Rather than delivering a rapid, sugary hit of nitrogen, they provide a more even diet that helps with roots, leaves and flower development.

March soils also tend to play along. They’re often damp without being waterlogged, allowing granules or pellets to break down steadily. Apply the same feed during a June heatwave and you can lose nutrients through evaporation, run-off or uptake by shallow roots.

The 11 perennials you really should feed in March

Spring feeding doesn’t affect every perennial in the same way. Some cope perfectly well with being ignored, while others genuinely reward a small amount of attention with fuller, longer flowering. These 11 are the plants that gain most from a March boost.

1. Roses: more blooms, fewer weak stems

Roses behave much like shrubs, yet many gardeners treat them as honorary perennials. They also feed heavily, and a March application usually pays back well.

• Use a balanced fertiliser around 10-10-10 or 12-12-12.
• Feed after pruning, scattering it in a circle around the drip line rather than right against the base.
• Lightly work it into the top layer of soil and water thoroughly.

This approach encourages sturdy new canes and plenty of buds, instead of skinny shoots that only manage a few flowers.

2. Peonies: feeding now for next year as well

Herbaceous peonies dislike being moved, so feeding is one of the few reliable ways to influence their performance. A March feed helps both this season’s growth and the flower buds being formed for the future.

Choose an organic or slow-release fertiliser with decent phosphorus and potassium. Apply it broadly around the clump, because established peonies often spread their roots widely. Don’t mound feed against the crown where the new red shoots appear.

3. Dahlias: building strong tubers and sturdy stems

Whether you’re starting dahlias indoors, in containers, or straight in the border, the first feed you give in March or early April sets expectations for the season. Too much nitrogen leads to lots of leaf and not much flower.

"For dahlias, choose a low-nitrogen feed such as 5-10-10 to prioritise flowers and strong tubers over leafy growth."

Mix the fertiliser into the planting area before you set out tubers or emerging shoots. Later, when growth accelerates, plants draw on this balanced store.

4. Delphiniums: tall spires need early support

Delphiniums deliver drama, but they ask for a bit in return. Feeding in March helps produce vigorous, upright stems capable of carrying heavy flower spikes.

Use a balanced fertiliser alongside plenty of organic matter. These plants thrive in fertile soil, yet they don’t cope well with sudden nutrient jolts, so slow-release pellets or well-rotted compost combined with fertiliser tends to work best.

5. Phlox paniculata: fighting mildew with nutrition

Border phlox are loved for fragrance and colour, but they’re also known for powdery mildew. Well-fed plants cope with stress more effectively.

A balanced fertiliser around 10-10-10 applied in March encourages strong clumps and plentiful blooms. Pair that with sensible spacing and watering at the base to reduce fungal issues later in summer.

6. Coreopsis: modest plants, generous flowering

Coreopsis aren’t the most demanding perennials, but a light spring feed can keep them blooming for months. In March, sprinkle a small amount of balanced fertiliser around the clumps, then add a thin compost mulch. Because excess nitrogen can make them flop, it’s better to underdo it than overdo it.

7. Bearded iris: flowers, not foliage

Bearded irises prefer relatively lean, free-draining soil and full sun. Heavy feeding-particularly anything high in nitrogen-pushes leafy growth at the expense of flowers.

"Use a low-nitrogen fertiliser such as 5-10-10 in March, keeping granules away from the rhizomes to avoid rot."

Spread the feed between the fans of leaves rather than on the exposed rhizomes. Good drainage plus modest feeding is what produces the best flowering stems.

8. Hostas: early feed before slug season

Hostas emerge in early spring with soft shoots that quickly expand into bold leaves. A gentle March feed supports this initial burst.

They do well with slow-release fertiliser combined with compost. Aim for a mild, steady supply rather than strong doses. Sound nutrition helps leaves bounce back from slug damage and maintain their size through summer, particularly in pots.

9. Daylilies (hemerocallis): long flowering needs reserves

Daylilies can bloom for weeks-sometimes months-opening fresh flowers day after day. That level of output draws heavily on stored energy.

In March, they benefit from a fertiliser that’s a touch higher in phosphorus and potassium. In borders where they perform strongly, repeat lightly in midsummer. This supports root strength and repeat flowering without driving excessive leaf growth.

10. Hydrangeas: colour and structure start now

Hydrangeas, especially blue types, react strongly to soil conditions. March is the moment to feed and adjust the balance before flower buds swell.

• For blue hydrangeas in acidic soil, use a fertiliser low in phosphorus, such as 12-4-8.
• In neutral or alkaline soil, feeding commonly nudges them towards pink shades.
• Add a light mulch after feeding to help keep moisture levels even.

Regular feeding leads to larger, more stable flower heads and sturdier stems that are less likely to flop in wet weather.

11. Astilbes: moisture lovers with an appetite

Astilbes thrive in damp, rich ground and are noticeably greedier than many other shade plants. If underfed, clumps can produce thin plumes and leaves that yellow.

"Give astilbes a balanced fertiliser in March, then again in autumn, paired with generous organic mulch to lock in moisture."

In shady, root-competitive borders under trees, this routine can turn spindly, patchy growth into full, feathery drifts.

How to apply fertiliser without harming your plants

A handful of simple habits can make the difference between feeding effectively and causing avoidable damage.

Action	Good practice in March	What to avoid
Soil condition	Lightly moist, not waterlogged or bone dry	Frozen, cracked or dust-dry soil
Placement	In a ring around the plant, then lightly worked in	Directly against the crown, collar or rhizome
Type of fertiliser	Organic or slow-release, matched to plant needs	Fast-acting, high-nitrogen lawn feeds
Watering	Water after spreading to start breakdown	Leaving granules dry on the soil for days

Before feeding, lightly roughen the surface with a hand fork to improve contact and reduce run-off. Water afterwards so nutrients move into the root zone, and so granules don’t scorch tender new shoots.

Avoid feeding frozen or parched soil, and never heap fertiliser at the base of stems. That combination can burn plant tissue, overstimulate weak foliage and still fail to produce strong flowering wood.

Weeding and recycling: a final March ritual that boosts blooms

While you’re feeding in March, it’s also the perfect time for quiet weed control. Annual weeds are still shallow-rooted and usually pull out easily by hand. Clear them early and you reduce competition for nutrients and light, giving perennials a genuine head start.

Those weeds can also become a free, mild liquid feed. Pack a bucket with chopped young weeds, top up with water, and leave it to steep for a couple of weeks. The resulting liquid-often referred to as plant “tea”-contains dissolved nutrients.

Strain it, then dilute to roughly one part liquid to ten parts water. Apply every couple of weeks around hungry perennials. It can pong, so many gardeners keep the bucket tucked away in a back corner, well away from seating.

Key terms gardeners quietly rely on

Fertiliser bags can seem like code, but a few basic ideas help you choose with confidence:

• N-P-K: The three numbers indicate the percentages of nitrogen (N), phosphorus (P) and potassium (K). A higher first number encourages leafy growth; a higher middle number supports roots and flowers; a higher last number improves overall toughness.
• Slow-release: Coated granules or organic feeds that break down over weeks, releasing a steady trickle of nutrients instead of a sharp spike.
• Balanced feed: A fertiliser where N, P and K are similar-such as 10-10-10-suitable for many flowering perennials.

Once you can read these labels easily, it becomes much simpler to match each perennial to what it actually needs, rather than reaching for the same general-purpose product every year.

Realistic scenarios: what happens if you skip March feeding?

For many gardeners, the real question isn’t which fertiliser to pick up, but whether March feeding genuinely makes a difference. In reality, the change can look minor at first, then become clear by early summer.

If you don’t feed, you may still get flowers, but typically on shorter stems and for a shorter season. Delphiniums and astilbes are more likely to lean or snap. Hydrangea heads often stay smaller. Coreopsis and phlox can run out of steam earlier.

If you feed sensibly in March, you shouldn’t expect instant fireworks. Instead, stems gradually become thicker, foliage looks deeper in colour, and flower spikes carry more blooms that are better formed. The contrast is most obvious during stressful spells-such as a dry June or an early heatwave-when well-nourished perennials cope better and recover more quickly once rain returns.

For gardeners who want long, dependable flowering rather than a one-week spectacle, that quiet March session with a bag of fertiliser and a hand fork can be the most influential task of the year.