If you are using slow release fertilizers for your roses, you should remember that they need to be applied less frequently - depending on the type of formulation of the fertilizer. Before applying this type of fertilizer, you need to remove the mulch and keep it aside, use a handheld cultivator to scratch the ground lightly and apply the fertilizer. Once you have applied the fertilizer, place the mulch back in position. The fertilizer will not produce the desired results until the soil and the fertilizer are in direct contact.
When you are using liquid fertilizers for your roses, they should be applied quite often - once in two weeks. Use a sprayer or watering can to apply the liquid fertilizer. You may dispense the liquid fertilizer on the ground using a watering can or alternatively spray the fertilizer on the foliage using a sprayer. In fact, the leaves as well as the roots of rose plants have the ability to absorb the nutrients in the fertilizer. If you apply the fertilizer straight away to the foliage, it will be absorbed as well as used by the plants faster. However, you should remember that you should never apply the liquid fertilizers to the plant's foliage when the atmospheric temperature is higher than 90°F, because the fertilizers will become more concentrated owing to quick evaporation at this temperature. As a result, the fertilizers may cause the plants to burn.
According to several experts, it is preferable to provide your rose plants with dormant feeding. Precisely speaking, dormant feeding denotes applying the fertilizers sometime during the end of the fall or in winter, when the plants do not have any top growth. However, the roots keep growing during the fall as well as in winter till the temperature of the soil drops below 40°F. They again start growing in spring prior to the emergence of the top growth. Therefore, the roots are able to absorb the fertilizers well during their dormant period, especially when they are ready to receive them. If you have fed your rose plants during their dormant period in the fall or during winter, you need not apply any fertilizer during spring. Dormant feeding of the rose plants is not required if you are residing in a warm area and the roses grow in your area throughout the year, unless you find that some plants have gone into forced dormancy owing to their extended life span or unless the growth of the plants slows down considerably during the fall and winter months.
As far as the amount of fertilizer that you need to apply to your roses is concerned, it is strongly advised that you always go by the instructions on the product label. This is important because the quantity will differ depending on the formulation you are using. For instance, if you are using a fertilizer with a formulation 5-10-5, you will be required to use it twice the amount of the fertilizer whose formulation is 10-10-10 in order to provide your plants with the same quantity of potassium and nitrogen.
At the same time, you should note that old garden roses, large shrub roses as well as rose climbers require additional fertilizers compared to the hybridized tea roses - almost two times more for each plant. On the other hand, miniature roses require about half the amount of fertilizers required by other roses. Therefore, it is important to adjust the amount of fertilizer you would be using for each variety of roses.
It has been found that fertilizers leach away faster when applied to sandy soils compared to other different types of soil. Therefore, if you are growing your roses in sandy soils, they need to be provided with fertilizers more frequently. In case you notice that the growth rate of your roses has been slowed due to the dearth of any nutrient, you should either rectify the soil or apply fertilizers more often - shortening the period between their applications by roughly one-third. If your roses are growing close to other plants, it may be necessary to provide them with approximately 20 percent additional fertilizers, especially when you notice indications of reduced growth of the plants.
In order to protect the roots from burning, you should ensure that you always apply any fertilizer to damp soil. Spread the fertilizer all over the area on the soil above the roots. Usually, the area should comprise the soil below which the plant's roots have spread. However, you should be cautious not to drop the fertilizer on the union of buds. In case you happen to do this by accident, water the area profusely with a view to wash away the fertilizer and protect the plant from burning due to the chemicals present in the fertilizer. Scratch the soil around the area of the plant, apply the fertilizer lightly using a handheld cultivator or a trowel. Water the plant and the soil around it properly after applying the fertilizer.
Never apply fertilizers to roses very late in the season, as this may prove to be harmful for the plants - mainly because nitrogen promotes new growths that will not get sufficient time to adjust themselves with the cold weather prior to them being damaged by the winter chill. Therefore, it is advisable that you should stop using any rose feed of complete fertilizer approximately two months or so prior to the first expected frost in your region.
On the other hand, you may apply fertilizers lacking in nitrogen content or containing very little proportion of this element, but having more phosphorus and potassium (for instance, super phosphate or a bone meal) at the beginning of fall. Both potassium and phosphorus facilitate the canes to acclimatize to the cold weather, thereby decreasing dieback as well as other injuries caused to the plants during the chill winter.
If you notice the foliage of your rose becoming brown or crisp, you should know that applying excessive fertilizers is the main cause for this. In such cases, you need to provide the plants with excessive water with a view to wash away the surplus fertilizer from the ground. Simultaneously, you need to take care to amend the concentration or amount of fertilizers that you apply in future with a view to prevent the problem from occurring again.
Apart from nitrogen, potassium and phosphorus, 10 other elements are necessary for the optimal growth of roses. These substances known as trace elements are required in very small amounts. They include calcium, copper, boron, chlorine, magnesium, iron, sulfur, manganese, zinc and molybdenum. While most of these elements can be found in the soil, air and water in adequate amounts, but you may need to supplement the plants with iron, calcium, sulfur and magnesium from time to time as there is a dearth of these elements in the largest part of the environment. Several fertilizers already contain these elements, but if the fertilizers you are using do not have them, you may purchase a supplement containing them. At times, there may be a scarcity of the other elements too, but that occurs rarely.
Dolomitic limestone is very useful for the optimal growth of roses, as it contains sufficient amounts of magnesium and calcium. In fact, magnesium is the crucial element found in chlorophyll and it helps the plants to utilize the most of the other nutriments, particularly phosphorus. Magnesium is also vital for production of leaves. When you apply dolomitic limestone to your plants, it is essential to go by the instructions on the product label. In case you are unable to get dolomitic limestone, you can provide your plants with magnesium in combination with 1 ounce or 2 ounces of Epsom salts, which is actually magnesium sulfate. After sprinkling appropriate amounts of Epsom salts on the ground in the region of your roses, scratch the soil gently so that it mixes with the soil well. Sulfur is also vital for roses, as it helps to encourage root growth, in addition to sustaining the deep green color of the plant and its leaves.
In addition, sulfur in its pure form or as compounds may be used to increase the acidity of the soil. Epsom salts and gypsum contain sulfur. Moreover, several inorganic fertilizers such as those that contain ammonium sulfate and iron sulfate also contain sulfur. You may also purchase agricultural sulfur in powdered form from any agricultural supply store or garden center. In case you are using pure sulfur, check the pH level of the soil with a view to ensure that adding the substance has not lowered the pH level of the soil excessively.
Iron is essential for roses for chlorophyll production. If there is a dearth of iron in the plants, their leaves will either become completely yellow or only the veins of the leaves will remain green. However, iron deficiency in plants can be treated by using chelated iron - a liquid or powder available at the garden stores. If you find that the leaves or the entire plant is turning yellow, a condition called chlorosis, spray this chelated iron on the plants. At the same time, you should examine the soil pH and if you do not find it appropriate, rectify it accordingly. This is because when you add iron to alkaline soils, this element is chemically not available to the roots of the plants. Remember that application of chelated iron to rose plants grown in alkaline/ base soils is just a first aid treatment. Therefore, it is important to ensure that the pH of the soil is appropriate. If it is not, adopt a permanent solution to correct the insufficiency.