Principles of Horticulture

Every gardening qualification starts with names, and for good reason: a common name is a rumour, and a botanical name is an address. "Bluebell" means one plant in England and a different one in Scotland; Hyacinthoides non-scripta means exactly one plant everywhere on Earth. The RHS Level 2 syllabus opens here because you cannot discuss anything else precisely until you can name it precisely.

The binomial system

A plant is a machine for turning light, water and air into more plant. Understand the machine and every practical technique — when to water, why to prune, what a feed actually does — stops being a rule to memorise and becomes something you can reason out. This is the plant-science heart of the Level 2 theory.

The three processes that run everything

Xylem, phloem, and why ring-barking kills

Two transport tissues run the length of a plant. Xylem carries water and minerals up from the roots. Phloem carries sugars from the leaves to wherever they are needed — roots, fruit, new shoots. The phloem sits just under the bark, which is why a rabbit or a strimmer that removes a complete ring of bark kills a tree: the roots are starved of sugar even though water is still rising. Understanding this one fact explains grafting, ring-barking, and why you never pile mulch against a trunk.

More gardens are made or broken by their soil than by their plants. The Level 2 syllabus treats soil as a system with a texture, a structure, a chemistry and a living population — and each of those is something you can assess and improve.

Texture versus structure

The nutrients, and what shortage looks like

Plants need three major nutrients in quantity: N (nitrogen) for leafy green growth, P (phosphorus) for roots and establishment, K (potassium) for flowers and fruit — the N-P-K on every feed label. Shortages show on the plant: overall pale, yellowing older leaves points to nitrogen; poor flowering and fruiting to potassium; yellowing between the veins of younger leaves often to magnesium. Reading these signs, rather than feeding blindly, is a Level 2 skill.

Making more plants

Propagation splits into two families. Seed (sexual) propagation mixes two parents, so seedlings vary — good for species, but a named cultivar grown from seed will not come true. Vegetative (asexual) propagation — cuttings, division, layering, grafting — makes exact clones of the parent, which is how every 'Stella' cherry and every named apple is produced. Cuttings are graded by the wood used: softwood in late spring from new growth, semi-ripe in late summer, hardwood in winter from dormant wood. Knowing which method suits which plant, and why, is examined directly.

The three kinds of problem, and IPM

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