Balanced fertilization will keep a plant healthy and encourage it to bloom profusely. To avoid burning the plant and for maximum efficiency, water the soil thoroughly before applying the fertilizer and use the amounts recommended on the label.
- First year: If the soil was well amended at planting time, no fertilizer is necessary. Otherwise, fertilize once after the first bloom cycle.
- Well-established roses: In May, use a high-nitrogen formula (e.g. 10-6-4) to promote leaf and stem growth. Early in July, use a high-phosphorous formula (e.g. 10-20-10) to stimulate the formation of new floral buds. Do not fertilize after the end of July so as not to encourage the growth of tender young canes that might not survive the winter.
Although they are fast-acting and rich in minerals, synthetic fertilizers do nothing to improve the soil structure or biological activity.
Before they release their nutrients, most natural fertilizers have to be broken down by organisms in the soil. This means that in addition to feeding the plants, they encourage biological activity in the soil. Most natural fertilizers are slow-acting but long-lasting in the soil.
- Granules: Scratch granules into the first few centimetres of soil around the plant, keeping them 20 cm away from the graft union, then soak soil thoroughly with water.
- Soluble powder: Mix with water and soak the soil or spray the leaves.
Rose fertilizers with magnesium are best. A handful of Epsom salts (125 ml per rose bush) scratched into the soil will also provide the plant with the necessary magnesium.