Are you a casual rose grower or a passionate exhibitor? The answer to that question can be a help as you develop your fertilizing routine. You may want to do a simple once or twice a year addition of granular fertilizer to keep things looking good, or weekly applications of a secret tonic that consistently wins you Queen of the Show. Whatever you choose to do to provide nutrients to your roses, when and how you do can have an impact on the results.
When to fertilize
Timing is everything! If you feed too early in the year, the seasonal rains may wash all your valuable nutrients away; too late in the season, the plants are starting to shut down and don’t need the extras. For established plants, time your application to maximize the benefit of your fertilizer so that nutrients are available to the plant when it needs it most – during the active growing and blooming stage. It generally starts around April when the weather has warmed the soil and slows down as the soil temperature drops – late September. The frequency of application will depend on what you’re after – bountiful blooms or that Queen of the Show, the quality of your soil, and the weather. If your roses are planted in healthy soil that is rich in organic materials, you generally don’t need to add any fertilizers until after the first big bloom.
When planting young roses without well-developed roots, a handful of bone meal (~2.0 – 28.0 – 0.2) can aid in development of roots, while organic materials like compost that break down slowly, provide a source of nutrition that won’t damage fragile root hairs. The addition of a time-released fertilizer at planting can also provide that steady stream of nutrients throughout the growing season, for 4, 6, or 8 months depending on the formulation. For these types of fertilizer, nutrient release is dependent on the soil moisture and temperature. Wait until the plant has gone through its first bloom cycle before applying chemical fertilizers.
To protect your plants from damage, make sure to water the plants thoroughly the day before and after fertilizing. Adding fertilizers, especially inorganic ones, to a dry plant can result in leaf burn or worse. Similarly, don’t fertilize on a scorchingly hot day; the plants are working hard just to stay hydrated, and the additional materials may not be of much benefit. Watering after fertilizing helps move nutrients into the root zone. When doing a foliar application of fertilizer, do it early in the morning when the liquids will be absorbed most quickly, won’t burn foliage and the leaves have time to dry completely.
How to apply fertilizer
How you apply fertilizer depends on what you are adding and when. For granular, powder or pelleted-type fertilizers, scatter them around the base of the plants and scratch lightly into the soil. Water-soluble products can be simply mixed in a watering can and applied directly to the plant, or if you’re fertilizing a larger number of plants, you may want to try a delivery device – ones that add concentrated liquid fertilizer to water at a specific rate. Called proportioners, they can be a hose-end sprayer with an adjustable dial that indicates the concentration of fertilizer you’re adding per gallon of water, a siphon device or an automated metering device. The siphon is a simple device with a connector that attaches to your water faucet and hose. It has a plastic or rubber tube connected to it; the unattached end is immersed in a container with a concentrated solution of water-soluble fertilizer. When you turn the hose on, the water pressure draws up the concentrated solution and mixes it with water to dilute the fertilizer as you apply it to your plants. The metering device functions in a similar way and can be added to your automated irrigation system to deliver a desired concentration of fertilizer every time you water.
The fastest route for providing nutrients is through the leaves – spraying a dilute solution of fertilizer directly on the foliage. Plants can absorb nutrients 8 – 20 times more efficiently through their leaf surfaces than through their roots. When using the foliar feeding approach, use a surfactant such as a mild soap (1/4 teaspoon/gallon of spray) to ensure coverage of the leaves, otherwise the spray may bead up on the foliage. Any application system that can provide a dilute liquid to the leaves will work (watering can, hose-end or backpack sprayer, etc.). Use a fine spray and spray until the liquid drips off the leaves. Also spray on the underside of the leaves where pores are more likely to be open.
If you’re growing roses in pots, use your solid or liquid fertilizer at one-half strength twice as often as roses in the ground, as watering flushes the fertilizer from the potted soil more quickly. Remember to water the rose well the day before fertilizing so there is less chance of burning the tender roots.
Finally, be gentle with your miniature roses, they can be sensitive to chemical fertilizers, so it’s wise to fertilize them at half-strength.