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Botanical families

The gardener's most powerful shortcut: know the family, and you already know a good part of the behaviour.

Watch the videoLes grandes familles botaniques au potagerAntoine le Potagiste

Explanation

Plants grouped in the same botanical family (Solanaceae, Legumes, Cucurbitaceae, etc.) often share their friends, their enemies, their pests and their needs. Learning the main families leaves far fewer pairings to memorise. But some families have their “rebels”, such as fennel or sunflower, and it is precisely those exceptions that set the apprentice apart from the accomplished gardener.

Refined definition

A botanical family groups together genera related by their evolution. What this means in practice: a similar floral structure, but also (very often) the same pests, the same diseases, the same soil needs, the same defence molecules. The family is a learning shortcut, not a fixed rule.

Key points

  • Why families share their behaviours

    Over the course of evolution, related plants have kept the same defence molecules (alkaloids in Solanaceae, glucosinolates in Brassicaceae) and the same needs. As a result, their predators (Colorado beetles, cabbage whites) and their diseases (blight, clubroot) pass between members of the same family.

  • The 9 main families to start with

    Solanaceae (tomato, potato) · Legumes (bean, pea) · Cucurbitaceae (squash) · Apiaceae (carrot, parsley, fennel) · Alliaceae (garlic, onion) · Brassicaceae (cabbage) · Asteraceae (lettuce, sunflower) · Lamiaceae (basil, rosemary) · Rosaceae (strawberry, apple tree). The game “Families & rebels” covers more, including the Amaranthaceae (beetroot, chard, spinach) and the Poaceae (maize).

  • The 3 great loners

    Fennel (an Apiaceae), reputed to hinder its neighbours (effect shown mostly in the laboratory); grow it apart as a precaution. Sunflower (an Asteraceae), with allelopathic compounds studied mainly against weeds: its extracts slowed wheat in pots (Anjum and Bajwa, 2010); as a precaution, do not dig its residues in just before sowing. Walnut (a Juglandaceae) releases juglone, which slows some sensitive plants, especially under an American black walnut (Juglans nigra); the common walnut (J. regia) rarely bothers its neighbours.

  • Application: rotation by family

    Rotation alternates botanical families first, then vegetable types (GAB/FRAB Bretagne), to break the cycles of parasites specific to a family. One classic rotation among others runs Legumes → Solanaceae → Cucurbitaceae → Root vegetables.

Watch out for

  • • “Family” is a useful shortcut, but always check the specific plant, especially for the Apiaceae (fennel has nothing to do with carrot) and the Asteraceae (sunflower ≠ yarrow).
  • • Cabbage clubroot (Brassicaceae) can contaminate the soil for up to 20 years (RHS): leave 4 to 5 years between two Brassicaceae crops (Réussir Fruits & Légumes, 2022), also counting radish, turnip and mustard, which are themselves hosts.

Examples

  • • Solanaceae: do not grow them in succession on a bed (shared blight)
  • • Legumes + Alliaceae: traditional avoidance, no effect on nodulation demonstrated in the field
  • • Three Sisters = Cucurbit + Legume + Grass, a complementary rule

Sources

  • The Angiosperm Phylogeny Group (2016). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. Botanical Journal of the Linnean Society, 181(1), 1-20.
  • Anjum, T. & Bajwa, R. (2010). Sunflower phytochemicals adversely affect wheat yield. Natural Product Research, 24(9), 825-837.
  • Réseau GAB/FRAB Bretagne : La rotation en maraîchage, fiche technique Fruits et légumes n° 16 (agrobio-bretagne.org)
  • RHS (Royal Horticultural Society) : Club root (rhs.org.uk/disease/club-root)
  • Réussir Fruits & Légumes (28/04/2022) : « Plasmodiophora brassicae, champignon responsable de la hernie du chou, peut survivre dans le sol plusieurs années »