Horticultural Practices
What the exam tests
Horticultural Practices covers how plants grow and how management decisions affect them: photosynthesis, respiration, transpiration, soil texture and pH, cation exchange capacity, essential nutrients, irrigation, pruning, and basic propagation. Expect questions that ask you to predict a plant response rather than recite a definition.
Core rules
- Photosynthesis converts light, carbon dioxide, and water to sugars; respiration uses those sugars. Shade, defoliation, and poor root health reduce stored energy.
- Soil texture (sand, silt, clay) drives drainage and nutrient holding. Clay has high CEC but low air porosity; sand is the reverse.
- pH controls nutrient availability. Most ornamentals perform at pH 6.0-7.0; acid-loving plants such as azalea, rhododendron, and blueberry need pH 4.5-6.0.
- N, P, and K are primary macronutrients; Ca, Mg, and S are secondary; Fe, Mn, Zn, Cu, B, Mo, Cl, and Ni are micronutrients.
- Prune spring-flowering shrubs right after bloom; prune summer-flowering shrubs in late winter or early spring. Remove no more than about 25-30% of live canopy in one year.
Worked example
A soil test for a mixed border reports pH 5.3. The bed contains lilac, which prefers 6.5-7.5, and azalea, which prefers 4.5-6.0. Reasoning: the two plants cannot both be optimized at one pH. Lime raises pH; elemental sulfur lowers it. At 5.3, azalea is acceptable and lilac is marginal. Options are to move the lilac to a separate bed and lime that bed toward 6.8, or raise the whole bed to about 5.8 and accept reduced lilac vigor. Do not apply lime and sulfur together; retest before adjusting again.
Traps
Remember that pH 5.0 is ten times more acidic than 6.0. A nitrogen deficiency cannot be cured by adding phosphorus. Overwatering fills soil pores and suffocates roots. Pruning a spring-blooming shrub in fall removes next year's flower buds.