Fertilize Roses

Feed for Health and More Blooms

Roses, in general, are heavy feeders. They love to eat, which positively affects their health. Did you know that a healthy rose not only produces more blooms, but is also better equipped to ward off pathogens too?

How-To-Fertilize-Page Grandiflora In Full Bloom

Roses can survive without being fertilized, but they struggle. There are exceptions to this rule: Species or near-species roses that are used to growing in the wild and have adapted to neglect. Selections like Rosa Mundi, Rosa glauca, or the Hybrid Rugosas; larger ramblers like ‘Darlow’s Enigma’ and ‘Paul’s Himalayan Musk’ can also fend for themselves. These varieties tend to be once-blooming, but are good choices for rose gardeners that don’t have the time or inclination to fertilize. But, anyone trying to grow repeat-blooming roses, like hybrid teas and floribundas, should fertilize regularly during the growing season.

 Paul's Himalayan Musk Covering a Tree
Rosa-Mundi-bush Rosa Mundi Bush In Full Bloom

Nutrients Roses Need to Grow

It helps to understand the basic nutritional building blocks that all plants need. Most important are the Big Three: Nitrogen (N), Phosphorus (P) and Potassium (K). These are the three numbers you see on all fertilizer packages, and are also referred to as the N-P-K ratio.

Without getting too scientific, if you can remember “Up-Down-All Around” you will have a good idea of how these nutrients operate:

  • Nitrogen helps shoots (above ground)
  • Phosphorus helps roots (below ground)
  • Potassium is used by the whole plant (like a vitamin).

More specifically:

Nitrogen (N) Promotes healthy vegetative, green growth. Nitrogen is a component of all proteins and because water washes it away from the root zone, roses require a consistent supply. It is needed to build chlorophyll and allows the plant to use light to turn water and carbon dioxide into sugars to feed itself. Too much and you produce lush plants with few or no blooms. Too little, and the rose will have yellow leaves, no new growth, and small pale roses.
Phosphorus (P) Makes for strong roots and abundant flower production. Too little will cause dull foliage, falling leaves, weak flower stems and buds that will not open.
Potassium (K) Also known as potash, encourages vigorous growth and makes sure all is in good working order. It is like an immune system booster that helps the plant through stressed times such as disease / insect damage, drought and cold temperatures. Lack of potassium will produce weak steams, poorly developed buds, and yellow edges on the leaves, which turn brown.

Roses need these nutrients too:

  • Calcium (Ca): Increases the strength of cell walls; enables a plant to better ward off sucking insects like aphids.
  • Magnesium (Mg): Crucial nutrient that promotes dark green leaves, intensified flower color, increased flower production, and can also help flush harmful salts through the soil. That’s why Epsom Salts (a form of Magnesium Sulfate) is a time-honored secret for rose gardeners. Apply at the rate of 1/3 to 1/2 cup per plant at the beginning of the growing season.
  • Sulfur (S)
  • Boron (B)
  • Copper (Cu)
  • Iron (Fe)
  • Manganese (Mn)
  • Zinc (Zn)

Choose the Right Fertilizer

So how do you decide which fertilizer is right? Is organic better than inorganic? The choice is ultimately yours, but remember this: ALL of the above nutrients are necessary for roses to thrive. Look for a balanced, high quality rose fertilizer that includes macronutrients as well as micronutrients. Roses make no distinction between the type of fertilizer they receive, as long as the nutrients are available.

Organic fertilizers include manures, compost, or other plant and animal products (alfalfa, bone meal, fish fertilizer, kelp extract, etc.).

  • Nutrient content is usually low, so use on a continual basis.
  • Better for the environment, builds humus and improves soil texture, and feeds soil micro-organisms. Healthy soil makes for healthy roses.
  • Price is normally higher for organics, but try making your own to save money (if you have access to organic material such as aged manure, kitchen scraps, composted yard debris, or lawn clippings.) Compost feeds the soil.
  • Fish/Kelp liquid fertilizer is a popular choice and has an N-P-K ratio of 2-1-2; fish provides a nitrogen source and kelp adds necessary trace minerals.
Liquid-Fertilizers Liquid Organic Fertilizers Are Very Effective

Inorganic (synthetic or man-made) fertilizers are manufactured and make up the bulk of what you can purchase ready-made at the store.

  • They offer ease of convenience, and are usually more concentrated, and less expensive than the organic products.
  • They are available in a variety of forms, including water-soluble (liquid), granular, and slow-release.
  • They do not help to condition the soil, so they have no positive residual effect.

When to Fertilize

The rule of thumb for granular fertilizer is every 4-6 weeks during the growing season.

  • Begin fertilizing when you have 4 to 6 inches of new growth, and can see the first real leaflet with 5 to 7 leaves. Actual weather condition, not a specific date, is what matters. Potential risk of spring frost damage is outweighed by the fact that your roses are hungry.
  • Stop fertilizing 8 weeks before you typically get a frost, if you live in a colder winter climate. This will allow any tender new growth to harden off, thereby reducing frost damage.
  • Fine-tune your applications for optimum rose health. Liquid fertilizers are more immediately available to the plant and can be used as a rescue treatment for plants with serious deficiencies. This includes foliar fertilizers that are quickly absorbed when sprayed on the leaves.
  • Apply fertilizers with little or no nitrogen content later into fall. This includes bone meal or rock phosphate, which helps promote root growth and next year’s blooms.

Fertilizer Tips from the Pros

  • Granular fertilizers are generally hard for young plants to process. Heirloom Roses recommends the use of a liquid fertilizer on younger rose plants during the first growing season to prevent burning of roots.
  • Roses grown in containers should be fertilized with water-soluble or liquid fertilizers on a more frequent basis. Since containers are watered more often, granular fertilizers are generally washed out before they can act).
  • Compost and mulch can rob the plant of nitrogen as it decomposes; it may be necessary to increase the level of nitrogen to counteract this process if you use compost or mulch.
  • Your local soil conditions have a lot to do with what nutrients are available to your roses. In Oregon, for example, phosphorus and calcium can easily bind with other elements in the soil and become unavailable. They need to be added more frequently or in higher concentrations to ensure they actually get to the plant. In other areas of the country, the soils are more alkaline and may require amendments to adjust the pH of the soil to ensure optimal fertilizer uptake.
  • Test your soil if you follow these basic fertilizing recommendations, have corrected your pH levels (roses like a pH of 6.0 to 6.5), and still have a nutritional issue. A soil test should help pinpoint the problem.
Healthy Happy Roses Healthy Happy Roses

Finally, remember to watch your roses closely and they will tell you what they need.

  • A rose with iron deficiency will lack chlorophyll in the leaves and will appear yellow with green veins.
  • A deficiency in manganese will also manifest itself in a lack of dark green leaf color.

Corrective action should always be taken when individual nutrients are not available to the rose plant.

Remember: Fertilizers are essentially salts. Without adequate water, they can burn your roses’ roots. In fact, most of these nutrients cannot be used without water moving into the plant. If your roses are growing in high humidity or excessively dry soil, nutrient uptake will be reduced. Always water your fertilizers in before and after application.

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