Description

Sweet Clover in flower.
Figure 1. Sweet clover in flower.
Sweet Clover by roadside.
Figure 2. Sweet clover by roadside.

Family

  • Leguminosae; species Melilotus spp.

Growth habits

Germination

  • White sweet clover have hard shells and need to be scarified prior to germination
  • Require the same strain of rhizobial bacteria as alfalfa for inoculation

Top Growth

  • Yellow sweet clover: 30–280 cm
  • White sweet clover: 100–200 cm, annual or perennial, grows as a 1 m stem
  • Flowers May-September; seeds in mid-to late fall

Root System

  • Strong taproot system — can penetrate up to 2 m
  • Can penetrate compacted silty and clayey soils

Overwintering

  • Seldom winterkills

Site suitability

  • pH tolerance 6.5 to 7.5
  • Average annual temperature range between 5° and 22° C
  • White sweet clover does well does on a wide range of soil textures
  • Tolerates calcareous conditions
  • Sweet clovers perform well in moderately well drained conditions

Sensitivity to herbicides

  • There are no herbicides available that are safe for use on sweet clover and control these broadleaf weeds.
  • Sweet clover is also sensitive to the soil residues of atrazine and some Group 2 herbicides.

Weed control

  • Sweet clover is frequently underseeded into a cereal crop and any weed control herbicide program must be:
    • safe to the cereal crop
    • effective on the weeds
    • safe to the cover crop
  • Usually the major weed control problems will be with winter annuals in fall seeded crops and with annual broadleaf weeds in spring cereals.

Benefits and cautions

Nutrient management

  • Fixes nitrogen and should be credited for N-additions; believed to move P and K to the root zone via its tap root system

Pest management

  • Attracts beneficial flowering insects

Organic matter

  • Biennial whites yield 2,200–3,500 lbs/ac (year 1) and 2,200–8,100 lbs/ac (year 2)
  • Yellow sweetclover 4,200–4,500 lbs/ac (year 1) and 5,500–8,500 lbs/ac (year 2)

Erosion control

  • Strong taproot said to reduce hard pan problems

Soil moisture

  • Shows intermediate values for water use efficiency

Getting started

Establishment

  • Plant in early spring — March–April
  • May need to be scarified
  • Needs to be covered lightly
  • Planting rate: 10–30 lbs/ac, depending upon variety. Most require 8–10 lbs/ac.
  • Seeding depth ~ 1.25 cm
  • Can be underseeded into corn

Cost and availability

  • Inexpensive to moderate cost (US $0.80 to $2.50/lb)
  • Most varieties suitable to Ontario conditions are widely available