Make plants grow taller by ensuring that their basic needs are being met. This includes water, sunlight, warmth and nutrients. Research the needs of your particular plant and provide these elements in the necessary amounts for optimum growth. Plants such as chrysanthemums and swamp sunflower grow taller in partially shaded areas while others such as southern blue flag require full sun to reach maximum height. Plants grow in poor soil, undesirable locations or without adequate water all the time, but they never reach their full height under such conditions.