When to Fertilize Roses (The Definitive Guide)


When to fertilize roses

In general, roses are hardy plants that will tolerate a range of conditions however they are heavy feeders and therefore a good fertilization regimen at the right time will produce the healthiest roses with the highest possible number of flowers.

Start to fertilize roses in April/May with Nitrogen, phosphate and potash fertilizer such as fish emulsion, and reapply it once per month until August 15th. Alfalfa and bone meal can be used in conjunction with fish emulsion and applied once every 4-6 weeks for best results.

The reason you should stop applying fertilizer after August 15th is that rose foliage needs time to prepare for its period of winter dormancy. The nitrogen in fertilizer stimulates new soft growth which is particularly susceptible to frost damage.

I recommend adding mulch such as compost, well-rotted horse manure or leaf mould around your roses at the start of spring to activate the soil’s ecosystem and mulch once more before winter to insulate the roots from the worst of the winter cold.

Roses tend to do best with a ‘balanced diet’ which means alternating and using fertilizers in conjunction with one another. This ensures that the soil ecology is healthy and the roses receive all the nutrients they need to be healthy and produce the most flowers.

When it comes to feeding roses the best results come with variety.

When to use Liquid Fertilizers for Roses

Fish emulsion can be applied to your rose bed in late April to early May (or until there is a diminished threat of frost) and then a once monthly application can be applied alongside other fertilizers until the middle of August.

Fish emulsion is a fast-acting short-term fertilizer that will infiltrate the soil and reach the roots more quickly than fertilizers that are in granulated form.

Fish emulsion also is high in nitrogen which is great for stimulating new growth and greening up foliage. This can be a problem however if the weather is too cold as the new softer growth is more susceptible to frost damage.

Always wait till at least late April/early May, just before the new leaves have fully opened and only apply if the nights are warming up consistently. If there is a late frost the new growth may be fine but if you see any damaged leaves (leaves that have gone black) then simply cut the growth off with pruners and your rose will be just fine.

Fish emulsion needs to be diluted into your watering can with a ratio of approximately 1 tablespoon per gallon of water. A typical watering can has a capacity of 2 gallons. This will serve one or two established rose bushes nicely as a welcome boost of nitrogen, phosphorous and potassium which are all major nutrients that are required in large amounts by roses.

Phosphorus is credited with stimulating the growth of roots, and stems and increasing flowering, for strong healthy roses.

Potassium is valued by your rose bush as it stimulates larger flowers and improves the plant’s resistance to drought and common diseases.

Fish emulsion is a great fertilizer for stimulating the soil ecology and directly feeding your nutrients but it is regarded as a short term fertilizer and ideally used in conjunction with other slower release fertilizers (such as alfalfa/blood and bone meal)  broader spectrum of nutrients.

By applying once per month you will ensure a healthy, disease-resistant rose that should put on a great floral display.

Stop applying fish emulsion in the month of August as the new growth that nitrogen stimulates needs time to harden up and prepare for the coming winter.

Be aware that the smell of fish will attract flies, cats and dogs if it’s not properly washed in so make sure you give the rose a good soak after application.

Applying some mulch, such as compost around the base of the plant will also help neutralize the smell and prevent insects.

When to Fertilize with Alfalfa and Bone Meal for Roses

You can start to add bone meal and Alfalfa fertilizers to roses from April and keep applying every 4- 6 weeks until August 15th when no new growth should be encouraged as the rose prepares for its winter dormancy.

Alfalfa and bone meal really complement the use of fish emulsion as they both break down and release fertility into the soil much slower, feed the soil microbes, improve the soil structure for better drainage and condition the soil to hold the right amount of moisture. 

Fish emulsion reaches the roots quickly but can also drain away into the soil quite quickly whereas alfalfa and bone meal nourish the soil over time for a more consistent release of nutrients.

Fertilizing with alfalfa and bone meal is very easy and they both give a generous hit of nutrients such as nitrogen, magnesium, zinc calcium, iron, and potash, all of which contribute to the health and disease resistance of roses.

Alfalfa also contains a growth stimulant called triacontanol which increases basal breaks in rose bushes for new shoots and subsequently more flowers.

Bone meal tends to smell and wild rabbits can eat alfalfa so it is always a good idea to rake back any mulch surrounding your rose and distribute the granules around the base of the rose and rake the mulch back over the top before giving a generous soak with the hose pipe.

This will prevent any unpleasant smells and encourage the meal and granules to start to disintegrate into the soil so that they reach the roots and cannot be eaten by wildlife

When to Apply Rose Formula or Chemical Fertilizers

The recommended application of any rose formula or chemical fertilizers will vary according to the manufacturer’s instructions which you should always refer to before use.

Generally, the advice is to apply a chemical fertilizer once you have pruned your rose in the spring and then another application after the first bloom. Sometimes a third application is recommended before the second bloom.

However, I must emphasize the importance of following the manufacturer’s guidelines as too much chemical fertilizer can burn the roots of your rose, so be diligent.

Too much fertilizer can do more harm than none at all so don’t be tempted to over fertilizer as it will not produce the result you are looking for.

My personal favourite Rose formula is Miracle-Gro rose mix. This pre-made formula contains all the nutrients a rose needs at the right concentrations. The granules only need to be applied twice during the growing season, once at the start of spring in April or May and then once more in July.

This is my favourite rose fertilizer that I personally use in my garden.
This is my favourite rose fertilizer that I personally use in my garden.

I personally use this fertilizer as it is so easy to use and has produced healthy roses that are laden with flowers. It is the perfect uncomplicated rose supplement.

When to Mulch for Healthy Roses

You can add mulch around your roses safely at any time of year without the concern of stimulating new growth too early or late in the season. Whilst mulch will add fertility to the soil, it breaks down slowly over time from the surface of the soil, as opposed to reaching the roots quickly as with liquid fertilizers.

Also with mulching the emphasis is more on feeding and improving the soil to benefit the roses rather than a direct feed to the rose roots.

Organic matter such as horse manure, leaf mould and compost all make fantastic mulch as they not only release nutrients in to the soil but also:

  • Improve soil structure so water drains easier, roots can move through the soil better to access water and nutrients.
  • Cools the ground in summer (roots prefer cool temperatures)
  • Keeps the worms and soil ecology busy as they feed on the decaying organic material and break it down into a chelated form that is concentrated with nutrients and much easier for the plant to take in.
  • Mulch has a much better capacity to absorb and retain water than most soils so that the roots of the rose can draw upon moisture when they need to.

Healthy soil equals healthy roses so always make sure you give your rose a good application or two each year.

The best time to add mulch is:

  1. At the start of the growing season in the spring, usually in March to stimulate soil ecology.
  2. A second application of mulch will be appreciated by your roses if the summer temperatures are high and the soil heats up and cracks. Rose roots like to keep cool and a layer of mulch will lower the temperature of the underlying soil.
  3. An application of mulch in the winter will pay dividends to the health of your rose as this will insulate the roots from the worst of the winter cold and give the roots a head start next spring.

Apply a 2-inch layer of mulch around the base of your rose ensuring that the mulch is not in contact with any of the canes (3 inches away is perfect) as the rose wood that is above ground does not like consistent exposure to moisture.

Conclusion

Mulch can be applied at any time of the year as a welcome boost to fertility and as a way of improving soil structure.

Apply fertilizer in the spring just before the leaves are fully open and apply once every 4-6 weeks during the growing season to produce the best blooms.

Whichever fertilizers you choose make sure that you do not apply them too early or late (before April and after August 15TH) as it will stimulate growth when the rose is getting ready for colder temperatures.

Alternating your fertilizers ensures your rose and the soil receive all the nutrients that they need to produce healthy, disease-resistant roses with plentiful flowers. 

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