At a glance
- Most perennials are modest feeders. Too much fertiliser harms more than too little: lush growth, fewer flowers, toppling stems.
- Ripe compost in spring covers the needs of the great majority of perennials. Hardly anyone needs mineral fertiliser.
- Know the three groups: heavy feeders want more, prairie and steppe plants almost nothing.
- A layer of mulch is half the fertiliser: it holds moisture, suppresses weeds and feeds the soil life.
- Fresh wood mulch locks up nitrogen short-term. Scatter some horn meal underneath and it balances out.
With feeding perennials the most common mistake is not too little but too much. Unlike hungry vegetables, most perennials are modest and manage on what a healthy garden soil offers anyway. Drown them in fertiliser and you often get the opposite of what you want: lots of soft leaf, little flower and stems that topple in the first summer rain. The good news: the right care is simple and cheap.
Less is more
Over-fed perennials grow lush and soft. They make a lot of leaf mass at the expense of flowers, become more prone to mildew and aphids and lose their stability. Especially the many drought-tolerant prairie and steppe plants in modern beds today react sensitively to an excess. They come from lean habitats and flower most beautifully on nutrient-poor soil.
The basic rule is therefore: first observe the soil, then help sparingly. A humus-rich soil supplied with compost carries most perennials without further fertiliser.
Compost: the standard fertiliser
For the great majority of perennials, ripe compost is the ideal food. It delivers nutrients slowly and evenly, improves the soil structure and feeds the soil life. One application in spring is usually enough for the whole year.
Apply in spring
In early spring, roughly CW 10 to 16, spread a thin one to two centimetre layer of ripe compost over the bed as the perennials come up.
Work in shallowly
Scratch the compost lightly into the top layer of soil with your hand or a cultivator. Deep digging is not needed and would only disturb roots.
Give heavy feeders extra
Give hungry perennials like delphinium or phlox some extra horn meal or organic fertiliser. The rest manage on the compost.
Feed after dividing
Freshly divided or planted perennials appreciate some compost in the planting hole so they establish well.
Heavy, medium and light feeders
Not every perennial is equally hungry. Know the rough grouping and you feed each group right.
How much nutrient does which perennial need?
- Heavy feeders
Delphinium, phlox, autumn asters, coneflower and daylilies want a rich soil and welcome an extra compost or horn meal application in early summer.
- Medium feeders
Most classic bed perennials sit here. A compost application in spring is plenty for them.
- Light feeders
Prairie perennials, steppe sage, stonecrop, mullein and many grasses like it lean. They need hardly any fertiliser and flower most beautifully on poor soil.
- The soil counts too
A heavy, humus-rich soil is more nutrient-rich anyway than a sandy one. Always adjust the feeding to your soil too, not just the plant.
Do not feed lean beds
If you have a bed of prairie perennials, grasses and steppe plants, resist the urge to feed. These plants flower and stand best on lean, free-draining soil. Fertiliser makes them soft and prone to toppling.
Mulching: half the fertiliser
Mulching is almost more important than feeding. A layer of organic material on the soil holds moisture in summer, suppresses weeds, protects against capping and, as it slowly rots, feeds the soil life and thereby the plants. Suitable materials are compost, dried lawn clippings in thin layers, leaves, perennial cuttings or bark mulch. Applied two to five centimetres thick, but not right against the plant base, or sensitive perennials rot.
Fresh wood mulch locks up nitrogen
Fresh bark mulch and wood chips draw nitrogen from the soil as they rot, which can weaken perennials. Before mulching, scatter a handful of horn meal per square metre and it balances out. Compost and leaves do not have this problem.
Feed the soil, not the plant, then the soil feeds the plant.
Perennial gardener's rule
The yearly rhythm
In spring, as the perennials come up, you apply the compost and mulch the bed. That is the main work done. Long-flowering heavy feeders get a second small portion of organic fertiliser in early summer. In autumn you leave cut-back, healthy perennial remains and leaves as natural mulch, or cover the bed thinly with compost; that protects the soil over winter and starts the cycle anew.
Enter the spring application as a recurring task in your garden journal. That way you feed your perennial bed correctly with a single move a year, and the soil gets better over time.
Common questions about feeding perennials
How often do I have to feed perennials?
For most perennials one compost application in spring is enough for the whole year. Only hungry heavy feeders like phlox or delphinium get a second small portion in early summer. Prairie perennials and lean beds need practically no fertiliser.
Which fertiliser is best for perennials?
Ripe compost is the ideal all-round feed: slow, balanced and soil-improving. If needed, supplement with organic fertilisers like horn meal. Mineral complete fertilisers are rarely necessary for perennials and quickly overdosed.
What should I mulch my perennial bed with?
With compost, leaves, dried lawn clippings in thin layers, perennial cuttings or bark mulch. Two to five centimetres thick, but not right against the plant base. With fresh wood mulch, scatter some horn meal underneath.
Why do my perennials flower little although they grow strongly?
Often that is a sign of over-feeding: too much nitrogen promotes leaves rather than flowers and makes the plant soft. Feed more sparingly, ideally not at all for lean-bed perennials, and provide enough sun.
Can I use lawn clippings for mulching?
Yes, but only dried and in thin layers. Fresh clippings applied thickly rot and smell. Spread thinly they are a good, nitrogen-rich mulch that rots quickly.
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