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Fertilizers For Roses

Like other flowering plants, roses need food in order to grow and bloom successfully. Roses, beautiful flowers, have greater nutritional needs than many other plants. Although small quantities of nutrients are available naturally in the soil and air, supplemental fertilizing is essential if you want your roses to perform their best. Your fertilizer must not only be of the right formulation for roses but also be applied in the right amounts at the right times.

Fertilizers contain three elements that are basic for rose growth: nitrogen, phosphorus, and potassium. Nitrogen promotes stem and leaf growth and deep green color and stimulates early spring growth. Phosphorus encourages root growth and flower production and is necessary for photosynthesis. Potassium helps regulate the metabolism of the rose and contributes to hardiness, vigor, good flower color, and disease resistance. A fertilizer containing all three elements is said to be complete.

Because plants differ in their nutritional needs, fertilizers come with differing proportions of these three elements. A typical formulation is 5-10-5, containing 5 percent nitrogen, 10 percent phosphorus, and 5 percent potassium (the other 80 percent is inert material that helps distribute them evenly). These percentages always appear in the same order on product labels. Two other common formulations of rose fertilizers are 5-10-10 and 8-12-4.

Roses, like many other flowering shrubs, grow best when you use a fertilizer whose nitrogen, phosphorus, and potassium exist in approximately 1:2:1, 1:2:2, or 2:3:1 ratios. The relatively lower proportion of nitrogen keeps the plants from producing lush leaves at the expense of flowers.

Super phosphate (0-20-0) and triple super phosphate (0-45-0) are special fertilizers used at planting time to encourage root growth. They supply only phosphorus.

Fertilizers are often referred to as organic or inorganic. Organic fertilizers contain carbon and may be either natural or synthetic. Natural organic fertilizers, such as bone meal, cottonseed meal, and fish emulsion, are minimally processed animal or vegetable by-products. Synthetic organic fertilizers, such as IBDU (isobutylidene diurea) and sulfur-coated urea, are manufactured from organic materials by more elaborate methods. Organic fertilizers of both types take the form of particles, granules, powders, or liquids.

Inorganic fertilizers are synthetic products containing no organic materials. They are manufactured from mineral salts, typically potassium nitrate, ammonium nitrate, ammonium phosphate, ammonium sulfate, calcium nitrate, potassium chloride, and potassium sulfate. These fertilizers are solids in their pure form but are often sold in solution.

Choosing fertilizers

Some organic and inorganic fertilizers are known as slow-release fertilizers because they release their nutrients over a long period, usually three to nine months. They are more convenient than the regular type because you don't need to apply them as often. Some slow-release fertilizers are applied only once per year in late winter or early spring whereas regular fertilizers are applied more frequently. The release is sometimes activated by soil moisture and sometimes by high soil temperature.

A good way to determine whether a fertilizer is the slow-release type is to look on the label for the percentage of water insoluble nitrogen. If the water insoluble nitrogen number is 30 percent or more, the fertilizer is considered slow release.

The labels of some products also indicate the number of months they will last. If you want to fertilize only once a year, choose a product that will remain active throughout your roses' growing cycle, whether it is four months, six months, or nine months. Note that slow-release products lack the trace elements that are present in many other fertilizers, so supplemental applications of these elements may be needed. Another important choice you face is whether to apply fertilizers in dry or liquid form. Although there are some natural organic liquid fertilizers, such as fish emulsion, the term liquid fertilizer usually refers to dry or liquid concentrates of water-soluble inorganic fertilizers that are mixed with water before application. Typical formulations are 20-20-20 or 15-30-15. Because of their water solubility, they are fast acting, releasing their nutrients quickly. This is a special boon for container grown roses, which must be watered frequently. Frequent watering of your flowers can cause dry fertilizers to leach away before they can act.

Liquid fertilizers are less appropriate for roses growing in the ground because they must be applied as often as once every two weeks. They are therefore not as convenient as dry fertilizers and are usually used only as a supplement. When you are deciding on which fertilizer to use in the garden, choose a slow-release type if saving time is one of your goals. Otherwise the best fertilizer to choose is one that combines organic and inorganic fertilizers. Use liquid fertilizer for your roses as a supplement if desired. For container-grown roses, liquid fertilizers are the best choice.

How and when to fertilize

Proper timing is essential when applying fertilizer because nutrients must be present in the soil when the plants need them most-at their most active stage of growth and flowering. This time will vary with the climate, but it starts with the first signs of growth in late winter or early spring and lasts until cool fall weather slows growth. Fertilizer must also be applied in the proper amount, which depends on the type and size of the roses, the length of the growing season, possible competition from other plants, and the soil.

Roses need to be fertilized often. Using a complete fertilizer or rose food whose N-P-K ratio is 1:2:1, 1:2:2, or 2:3:1, feed roses as soon as they are pruned, after the first flush of bloom, and about two months before the first fall frost. Gardeners who want to grow exhibition-size roses can feed them once a month from early spring to late summer or fall, depending on the length of the growing season. They can also use liquid fertilizers in advance of rose shows to produce better specimens.

If the soil pH needs to be adjusted, it should be done about a month before fertilizing to create the optimum pH for roses, which is 6.5. The more efficient nutrient absorption at this pH will make your fertilizer go further.

Slow-release fertilizers

Slow-release fertilizers need to be applied less often, at a frequency that depends on the formulation. When applying slow release fertilizers, it is best to move the mulch aside, lightly scratch the fertilizer into the ground with a handheld cultivator, then put the mulch back. Unless the fertilizer is in contact with the soil, it will not work properly.

Liquid fertilizers

Liquid fertilizers must be applied as often as every two weeks. Pour them over the ground with a watering can or a sprayer, or spray them on foliage with the same equipment. Leaves as well as roots can absorb nutrients; in fact, fertilizer applied directly to the foliage will be put to use more quickly. Do not apply any liquid fertilizers to foliage when the air temperature is over 90 F, since rapid evaporation at these temperatures makes the fertilizers more concentrated and thus more likely to burn the plants.

Dormant feeding

Many experts recommend dormant feeding, which is the application of fertilizer during the late fall or winter when the plant tops are not growing. Because roots continue growing in fall and winter until the soil temperature falls below 40F and start growing again in spring before top growth appears, they can absorb fertilizer supplied during the dormant period as soon as they are ready for it. If roses are dormant fed in fall or winter, an early spring application of fertilizer is not necessary. In warm areas, where roses grow all year, dormant feeding is not needed unless the plants are forced into dormancy to prolong their life, or unless their growth slows significantly.

Fertilizer amounts

Always follow the directions on the label regarding the amount of fertilizer to apply since this will vary with the formulation. It takes twice as much 5-10-5 fertilizer as 10-10-10 fertilizer to provide plants with the same amount of nitrogen and potassium.

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Large shrub roses, old garden roses, and rose climbers need more fertilizer than hybrid teas roses-about twice as much per plant. Miniatures roses need much less than any other rose-about half as much. Adjust your applications accordingly.

Because fertilizers leach more rapidly from sandy soils than they do from other types of soil, they may need to receive fertilizer more often. If you see signs of reduced growth from nutrient deficiency, either correct the soil or shorten the interval between fertilizer applications by about one-third. When roses are growing near other plants, they may need about 20 percent more fertilizer if they show signs of reduced growth.

To keep from burning the roots, always apply any type of fertilizer to moist soil, spreading it over the entire area under which roots are growing. Generally this is the soil under the spread of the plant. Be careful not to spill fertilizer on the bud union. If you do so accidentally, wash the fertilizer off to avoid burning the plant. Work the fertilizer lightly into the surface of the soil with a trowel or a handheld cultivator and water again.

Stop fertilizing before cold weather

Fertilizing too late in the season can be detrimental to roses, as nitrogen encourages new growth that will not have time to adapt to the cold before winter chill can damage it. It is best to stop using complete fertilizers about two months before the first frost.

However, a fertilizer that contains little or no nitrogen but has phosphorus and potassium (such as bone meal or super phosphate) can be applied in early fall. Phosphorus and potassium help the canes adapt to cold weather, lessening dieback and other winter injury.

Avoid overdoing

If rose foliage turns crisp and brown, it may be a sign of over fertilizing. Water the plants heavily to leach excess fertilizer out of the ground, and adjust the amount or concentration of future feedings to keep the problem from recurring.

Trace elements

In addition to nitrogen, phosphorus, and potassium, roses require small quantities of 10 other elements, called trace elements, for proper growth. These elements are boron, calcium, chlorine, copper, iron, magnesium, manganese, molybdenum, sulfur, and zinc. Most already exist in sufficient amounts in the soil, water, or air. But calcium, magnesium, sulfur, and iron may need to be supplemented occasionally because they are scarce in most environments. Sometimes they are present in fertilizer formulations. If not, you will have to purchase a supplemental source. Deficiencies of the other trace elements are possible but rare.

In addition to containing calcium, dolomitic limestone also contains magnesium, the basic element in chlorophyll that enables plants to utilize other nutrients, especially phosphorus. Magnesium is also essential for leaf production. If you are applying dolomitic limestone, follow the directions on the product label. If dolomitic limestone is not available, magnesium can be supplied with 1 to 2 ounces of Epsom salts (magnesium sulfate) per rosebush. Sprinkle Epsom salts over the ground and work it into the soil. Sulfur promotes root and top growth and helps maintain a dark green color.

Sulfur, either pure or in some compounds, is also used to acidify the soil. Sulfur is present in gypsum and Epsom salts, and in many inorganic fertilizers, including those containing iron sulfate or ammonium sulfate. It is also possible to buy powdered agricultural sulfur at garden centers or agricultural supply stores. Check the soil pH after adding pure sulfur to make sure that it hasn't lowered the pH too much.

Iron is needed for the production of chlorophyll; if iron is lacking, leaves turn completely yellow or stay green only along the veins. A solution of chelated iron, a powder or liquid sold at garden centers, can be sprayed onto plants if this yellowing, known as chlorosis, occurs. Also check the pH of the soil and correct it if necessary because iron in alkaline soils is chemically unavailable to plant roots. Applying chelated iron to roses in alkaline soil is only first aid; adjust the pH to correct the deficiency permanently.

The magic of manure

As food passes through an animal, its composition is altered. Fresh manure contains a high percentage of ammonia. This is partly why manure has such a pungent smell. Ammonia is high in nitrogen and is a readily available source for plants. As soon as the manure is exposed to the air, however, the ammonia begins to evaporate and the nitrogen is lost to the atmosphere. As well, rain percolates through the manure, leaching out the nitrogen. So while fresh manure is a good source of nitrogen, older, exposed manure, although still valuable for its organic content, is not nearly as valuable as fertilizer. A good farmer will work fresh manure quickly into the soil so that the nitrogen will not be lost.

You should be cautious of fresh manure. The ammonia it gives off poses a danger to plants. Plants are nitrogen hogs, and will absorb nitrogen as long as it is available. Fresh manure near a plant's roots provides a tremendous quantity of nitrogen. As long as adequate water is available to the plant it will be able to handle the nitrogen. However, if water is limited in any way, the nitrogen will form salts in the plant's tissues, which will burn the plant up. Manure also contains the bane of gardeners everywhere -weeds. Many weed seeds pass through animals without harm. Once put into the soil with the manure, they have not only a place to grow but the nutrition to grow well.

If we want to use manure to best advantage we need to convert the nitrogen to a more stable form and to eliminate the problem of weed seeds. The answer is to make compost.

The miracle of compost

If you know how to make a complete, balanced compost, you do not need any other plant food. Well-made compost should contain all the nutrients needed for healthy growth. It will contain the bacteria, fungi and other microscopic life that work to control diseases in soil, and it will provide valuable organic matter.

The secret of good compost lies in balance. Bacteria in a compost pile feed on the carbon in the organic material and convert it into energy. The bacteria require nitrogen, phosphorus and potassium, among other elements, to accomplish this task. Although phosphorus and potassium are available in the organic material, nitrogen is usually in low supply. We need to add nitrogen to the pile. Fresh manure is the most common source of nitrogen for compost makers, but it is not always available. Many nitrogen-rich materials can be purchased at local animal feed- stores. These include linseed meal, Soya meal, cottonseed meal, blood meal, bone meal and feather meal. If you live near the sea you may be able to obtain fish or shellfish waste. Any of these, or similar high-protein materials, provide the nitrogen necessary to get your compost working.

A balance must be struck between the carbon and the nitrogen in the pile. The proper ratio for optimum compost activity is 30 carbon to 1 nitrogen. To achieve a healthy compost pile with a well-balanced carbon/nitrogen ratio, start as follows:

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Spread your organic material into a layer approximately 1 ft. (30 cm) thick. This might include materials like old hay, vegetable peelings, leaves (preferably shredded) or weeds. On top of this, spread a layer of fresh manure approximately 3 in. (8 cm) thick. If you cannot obtain manure, put a thinner layer of whatever organic nitrogen source you can obtain. If you are unable to obtain any organic sources of nitrogen, sprinkle a fertilizer such as urea (42-0-0) very lightly over your organic matter. Sprinkle a few shovelfuls of earth over the whole lot. This earth contains enough soil bacteria to act as a starter for the breakdown process, although many argue that it is not necessary. If you want a sweet (high pH) compost, add a shovelful of lime. Repeat this layering until the pile is about 4 ft. (1.2 m) tall. As you layer your pile, be sure to add enough water to make it thoroughly moist but not soggy.

Once your pile is built, turn it regularly. Turning a compost heap puts oxygen into the pile. This oxygen is vital to keep the bacteria active. Some compost heaps never breakdown properly due to lack of oxygen. Turning every day or two is ideal. If you can turn your pile once a week, or at most once every two weeks, the compost will work well. After one or two turnings, your compost heap should be steaming hot inside. A properly balanced and aerated compost pile will reach temperatures of 160F (72C). These high temperatures destroy the weed seeds and any harmful diseases that may be present in the materials. Remember that the size of your pile is not very important. Even a small compost pile will work well if there is a proper carbon/nitrogen balance and if it is damp and turned regularly. If space is limited or tidiness a concern, there are many compost makers available that are easy to use.

Once it cools, your compost is ready to use. In the garden it will continue to break down, and as it does so, it will slowly release the nitrogen and other elements your plants need. If your quantities are limited, use it as a side dressing around your plants or incorporate some in your planting holes. If you have larger quantities, use it as a general top dressing on your garden. If you make composting a regular part of your garden program you will see the results in healthy growth and good flowering.

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