This is the hand-out from Dennis Eveleigh at his presentation of Growing Roses Organically How to Thrive Without the 10-25-5, which was part of the Green Gardening 2004 held at the Royal Botanical Gardens on Saturday, 28 February 2004. (The items in italics are my own notes from the presentation.)
Successfully Growing Roses Organically
Treating Fungal Diseases (Black spot, powdery mildew, rust, etc.)
- Sodium bicarbonate (baking soda) + horticultural oil + water
Controlled frequent sprays of an aqueous mixture of Sodium bicarbonate and horticultural oil have shown to reduce/control powdery mildew and black spot.
The formula works out to 3 teaspoons of baking soda and 2.5 tablespoons of summer-weight horticultural oil mixed in a gallon of water. The first spray should be at leaf break. (Spray on a 7 to 10 day cycle.)
Sulfur has been used for centuries to control diseases and pests. Sulfur is effective against powdery mildew, black spot and rust. However, sulfur is moderately toxic to humans and other animals. Sulfur is a nonspecific pesticide and may kill beneficial insects as well. Spraying sulfur at temperatures above 80 degrees F may burn the plant. It is also not very attractive on the plants foliage.
Combatting common rose pests (aphids, spiter mites, thrips, midges, beetles, etc.)
- Insecticidal soaps/detergents
Salts from the fatty acids in soaps act as selective insecticides. They are able to penetrate the insects cuticles and as a result, the cell membranes collapse and leak. This causes dehydration. Soaps are especially effective on soft-bodied insects like aphids, mites and thripes, but they are less effective on chewing insects like caterpillars and beetles. These sprays should not be used for plants with thin cuticles. These soaps and detergents biodegrade rapidly in the soil and are harmless to plants and animals. Pure soap can be used when making a homemade spray treatment. (Palmolive dish soap. Spray on a 7 to 10 day cycle.)
- Diatomaceous earth
DE is an abrasive dust used as an insecticide. Its mechanism is by physical action, rather than chemical action. The dust consists of fossilized silica shells of algae called diatoms. The microscopic shells of diatoms are covered in sharp, needle-like projections that are able to penetrate cuticles of insects. This causes the insects vital liquids to leak out. DE also works by absorbing the waxy coatings on the insects bodies. As a result of these two mechanisms, the insects die of dehydration. It is important to dust both the plants and soil. DE can kill slugs, snails, and other soft-bodied insects such as aphids and thrips. This insecticide is non-selective. (Use inside for airwigs, etc.)
- Dormant/horticultural oil
Oils are able to control insects such as aphids and mites. They can even kill weeds by dissolving their cell walls but they are not registered for this use. Light oils are able to break down quickly and are only slightly toxic to mammals and humans.
Feeding Roses (organic fertilizers, mulch)
For older/lower leaves (growth):
Source of Nitrogen
- Alfalfa meal, Blood meal, Fish emulsion, Guano, Soybean meal
Source of Phosphorus
- Bonemeal, Colloidal phosphate, rock phosphate
Source of Potassium
- Granite meal, Greensand, Sul-Po-Mag, Wood ashes
Source of Magnesium
- Dolomitic lime, Epsom salts
Source of Zinc
- Chelated zinc spray, Kelp extract, Kelp meal
For younger/upper leaves (growth):
Source of Calcium
- Gypsum lime, Oyster shells
Source of Iron
- Chelated iron spray, Kelp extract, Kelp meal
Source of Sulfur
- Flowers of sulfur, Gypsum
Source of Copper
- Kelp extract, Kelp meal
Source of Manganese
- Kelp extract, Kelp meal
Source of Molybdenum
- Kelp extract, Kelp meal
Many gardeners prefer to use organic fertilizers one that ocure naturally over chemical-based fertilizers. Organic fertilizers, such as fish emulsion, composted manure (fresh manures can burn plant foliage), and blood meal (dried animal blood, which is high in nitrogen), add organic matter to the soil and contribute to healthy soil and thus healthy plants.
One successful formula is composed of equal amounts of alfalfa meal and cotton seed meal. Ten cups of this formula re spread at the base of each plant every ten weeks and then covered with a thick mulch of compost.
You can grow superior roses if you feed them with liquid fish emulsion fertilizer (mix concentrate with the recommended amounts of water) watered on to roses. Compost tea (a shovel of compost in a 20 litre pail of water) watered onis also a wonderful fertilizer for summer rose feeding.
Another suggested treatment:
In early spring, apply a top-dressing of compost, 1/2 cup of rock phosphate or bone meal and 1/2 cup of greensand. Also, water all plants with a tablespoon of Epsom salts dissolved in 4.5 litres of water. Give a liquid foliar feed every 2-4 weeks up until August using fish and kelp or seaweed emulsion. For the final feed of the season, make sure to use a fertilizer without nitrogen to prepare the roses for winter dormancy.
Using mulch reduces weeds, keeps the soil temperature stable, and reduces moisture loss from the soil. When the mulch breaks down, it adds organic matter, conditioning the soil and adding nutrients.
Types of organic mulch that can be used:
- Shredded bark
- Well-rotted manure
- Chopped leaves
- Pine Bark Nuggets
- Wood chips
- Wood shavings
- Peanut shells
- Pine needles
- Buckwheat hulls
- Cocoa Bean shells
Cultural practices that should always be practised
The are some basic methods that are important to follow in order to prevent disease:
- Buy certified, healthy stock, buy resistant roses, make sure there are no signs of powdery mildew or black spot.
- Space plants out enough to provide good air circulation (this helps to keep foliage dry at night).
- Water from the base of the plant, water early in the morning to give foliage a chance to dry during the day.
- Use sterile and sharp shears when pruning (clean pruning shears with bleach and water or wipe with alcohol).
- Seal cuts with non-toxic glue (Elmers), prune properly to keep canes open and airy.
- Weed regularly, they may act as hosts for insects that prey on the roses, they may also be carrying disease.
- Use mulch for healthy root growth, this promotes beneficial soil microorganisms, also stops rain and water from splashing and possibly spreading disease organisms/fungal spores, mulch also good for worms.
- Remove and dispose of infected leaves or plant parts to avoid spreading of disease (especially in the fall).
- Keep rose beds free of debris, pick up any fallen leaves, flowers.
- Remove all mulch and debris in autumn, they may contain fungal disease spores.
- Interplanting roses with other plants (allium/onion family, marigolds, parsley, etc.) May help to reduce pests and disease, however, this is controversial whether it works or not (chives may prevent black spot and fungus).
- Use organic methods to control insects (pick then off by hand, organic traps, natural predators, organic sprays).
- Occasionally, spray infected leaves of roses with strong streams of water, this helps to remove and reduce powdery mildew spores. However, make sure this is done early inthe morning to prevent black spot! (Olson and Whitman, 1998).