Fertilising guide

How to fertilise Rhododendron 'Catawbiense Boursault' (Rhododendron catawbiense 'Boursault')— schedule & NPK

Also called Boursault rhododendron.

More about rhododendron 'catawbiense boursault'

About Rhododendron 'Catawbiense Boursault'

Rhododendron catawbiense 'Boursault' · also called Boursault rhododendron · flowering

Rhododendron 'Catawbiense Boursault' is a tough, large, evergreen hybrid bearing rounded trusses of lilac-purple, lavender flowers in late spring. Derived from the cold-hardy Catawba rhododendron, it withstands harsh winters and suits acidic woodland borders and screens. All parts contain grayanotoxins and it is ASPCA toxic to cats and dogs.

Growth habit: Large, dense, rounded evergreen shrub with leathery dark-green leaves; vigorous and spreading, forming a substantial mound over time.

What fertiliser rhododendron 'catawbiense boursault' actually wants — and why

Rhododendron 'Catawbiense Boursault' is an acid-loving plant — it can only take up nutrients in acidic soil, so the feed itself matters less than using an ericaceous formula and never liming.

For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for rhododendron 'catawbiense boursault': match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.

How often to feed rhododendron 'catawbiense boursault', and which months

Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For rhododendron 'catawbiense boursault':

Feed once in early spring after flowering with an ericaceous (acid) fertiliser; a second light feed in early summer is optional. Avoid high-nitrogen or late feeding. Mulch annually with leaf mould or composted bark to nourish surface roots. In practice: an ericaceous feed in spring as growth resumes, repeated through the main growing months; never apply lime, bonemeal or wood ash, which raise pH.

The dormant-season rule matters more than the exact interval: skip feeding entirely when rhododendron 'catawbiense boursault' is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.

What strength to mix for rhododendron 'catawbiense boursault'

Follow the ericaceous product's own rate — these are formulated for the plant, so the dilution on the label is right for rhododendron 'catawbiense boursault'. The variable that actually matters is pH, not concentration.

Feeding always goes onto already-damp soil, never dry roots — water rhododendron 'catawbiense boursault' first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the rhododendron 'catawbiense boursault' watering schedule.

Signs you are over-feeding rhododendron 'catawbiense boursault'

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for rhododendron 'catawbiense boursault':

Brown, scorched leaf margins from too strong or too frequent a dose.
White salt crust on the soil surface.
Soft, lush growth that fruits or flowers poorly.

Signs you are under-feeding rhododendron 'catawbiense boursault'

Yellowing leaves with green veins (iron chlorosis from high pH).
Weak growth, poor cropping and an overall pale, stressed look.
Stunted new shoots in spring despite adequate water and light.

If the symptoms point at watering, light or roots rather than nutrition, the full rhododendron 'catawbiense boursault' care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Flush rhododendron 'catawbiense boursault' with rainwater (not hard tap water, which raises pH) if salts build up; better still, mulch with pine needles or composted bark and water with rainwater to hold the acidity.

Organic vs synthetic feeds for rhododendron 'catawbiense boursault'

Organic options

Composted pine bark, pine-needle mulch, used coffee grounds and an organic ericaceous feed gently maintain acidity. UK: Vitax or Westland Ericaceous; US: Espoma Holly-tone or Dr. Earth Acid Lovers. Slow, soil-improving, hard to overdo.

Synthetic / liquid feeds

A liquid or granular ericaceous feed — UK: Miracle-Gro Ericaceous, Vitax or Westland; US: Miracle-Gro Acid-Loving Plant Food or Espoma Holly-tone. Pair with rainwater and an acidic mulch for it to work.

Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.

Fertilising rhododendron 'catawbiense boursault' — frequently asked questions

What fertiliser does rhododendron 'catawbiense boursault' need?

An ericaceous (acidic) fertiliser, formulated to keep the soil pH low and supply iron and trace elements in a form acid-loving roots can absorb. Ordinary feeds and any lime lock out iron and yellow the leaves. Rhododendron 'Catawbiense Boursault' is an acid-loving plant — it can only take up nutrients in acidic soil, so the feed itself matters less than using an ericaceous formula and never liming.

How often should I feed rhododendron 'catawbiense boursault'?

Feed once in early spring after flowering with an ericaceous (acid) fertiliser; a second light feed in early summer is optional. Avoid high-nitrogen or late feeding. Mulch annually with leaf mould or composted bark to nourish surface roots. Feed once in early spring after flowering with an ericaceous (acid) fertiliser; a second light feed in early summer is optional. Avoid high-nitrogen or late feeding. Mulch annually with leaf mould or composted bark to nourish surface roots. In practice: an ericaceous feed in spring as growth resumes, repeated through the main growing months; never apply lime, bonemeal or wood ash, which raise pH.

What strength of feed for rhododendron 'catawbiense boursault'?

What does over-feeding rhododendron 'catawbiense boursault' look like?

Brown, scorched leaf margins from too strong or too frequent a dose. White salt crust on the soil surface. Soft, lush growth that fruits or flowers poorly. Feeding rhododendron 'catawbiense boursault' an ordinary fertiliser, or growing it in hard tap water / limey soil, is the defining mistake — it triggers lime-induced chlorosis (yellow leaves, green veins) no amount of feeding fixes until the pH comes down.

Should I flush the soil of rhododendron 'catawbiense boursault'?