The Rose-Phosphate-Mycorrhizae Connection

The Rose-Phosphate-Mycorrhizae Connection

by Rita PerwichConsulting Rosarian, San Diego Rose Society.

Rosarians generally spend a lot of time tending to their roses. Plain and simple: a beautiful rose garden requires dedication and care. What if you find out that some of the practices you have been dutifully following may not be good for your roses? I know that thought turns me inside out and upside down! Which aspects of rose care should be re-examined? Are there any that should be retired from practice? Are we wasting our time and our money, and worse yet inadvertently harming our soil and our roses with some of our good intentions? The use of phosphorus fertilizer and myccorhizal activity in our soils are two topics that bear on each other and need to be examined.

(ABOVE: ‘Julia Child’ by Rita Perwich.)

 

Phosphorus:

A handful to a cupful of phosphate fertilizer placed in the bottom of the planting hole by rosarians is common practice because phosphorus is not mobile and rosarians want to ensure the rose has adequate phosphorus for root development and beautiful blooms. In San Diego, we continue to add this macronutrient to our fertilizing regimen which commences in early spring and ends in mid-October.

 

Mycorrhizae:

A few years ago many of us had not heard of mycorrhizae. Now we all want to have it in our soil. Mycorrhizal fungi in the soil have been symbiotic ‘plant partners’ for millions of years. Roots of plants under mild nutritional stress release chemical cues that stimulate mycorrhizal growth. The mycorrhizal hyphae penetrate cell walls of these receptive roots creating passageways between the partners. Large networks of fine filaments or hyphae extend beyond the root mass helping plants access soil water and mineral nutrients from otherwise inaccessible areas. In return, since mycorrhizae are non-photosnythetic and unable to produce their own food, the plant transfers back nutrients through the hyphae to its symbiotic partner.

 

Benefits to Plants Colonized by Mycorrhizae:

  1. The mycorrhizal network increases root mass which helps provide plants with a more consistent water supply enabling the plant to keep its stomata open longer and thereby assisting the plant in the process of photosynthesis;

  2. One of the main benefits of mycorrhizae is the mobilization and uptake of phosphorus which is especially important in alkaline or nutritionally deficient soils. Mycorrhizae can easily solubilize rock phosphate which is difficult for plant roots to mobilize. When plant roots perceive a lack of available phosphate, they are receptive to mycorrhizal infection and subsequent uptake of this phosphate source;

  3. Colonization of plants by mycorrhizae provides more resistance to pathogens such as Verticulum, and pests, including nematodes, and limits the available space for colonization by other pathogens;

  4. Mycorrhizae can protect uptake by the roots of toxic minerals such as aluminum, chromium and lead;

  5. Mycorrhizae release enzymes that free nutrients from the soil for plant use reducing the need for additional fertilization;

  6. Mycorrhizae can ameliorate salt stress.

 

Mycorrhizae can be Damaged

Mycorrhizae can be damaged and unable to function when there is soil disruption, contaminants in the soil including fungicides, and excessive fertilizer application, especially fertilizers containing soluble forms of phosphate. The reason for this is that in nutrient-rich, and also adequately watered soils, plants are less dependent on mycorrhizae causing the fungi to retreat and remain inactive.

The Rose-Phosphorus-Mycorrhizae Connection

In her article entitled The Myth of Phosphate, Part II Dr. Linda Chalker-Scott, associate professor and extension urban horticulturist at Washington State University, states that although there is plenty of rose literature advocating phosphorus fertilizer for root and flower growth, she finds no scientific evidence that roses need high levels of phosphate. In fact, studies show that excess phosphorus in the soil is detrimental to plants and can result in leaf chlorosis. This is because excess amounts of phosphorus in the soil limit the uptake by the plant of other essential nutrients such as iron, manganese and zinc. Chalker-Scott writes that like most other perennial landscape plants, roses are rarely deficient in any nutrient other than nitrogen. “Addition of any non-deficient nutrient to a landscape is a waste of time and money, and can injure soil organisms.” She adds that this is particularly true of the mycorrhizal associations that occur between various fungi and plant roots. In another article, Mycorrhizae. So, What the Heck Are they Anyway? Chalker-Scott states that numerous studies have shown that when a plant senses that its tissues or the soil contain enough phosphate, it no longer needs its mycorrhizal partner and so becomes less receptive to infection by mycorrhizal spores. She stresses plainly that phosphate fertilizer is deadly to mycorrhizal associations, “To encourage these hard-working and beneficial fungi in your plant community, you’ve got to cut down the junk (plant) food — stop using phosphate fertilizer.”

 

Encouraging Mycorrhizal Colonization

To encourage mycorrhizal colonization, Chalker-Scott stresses the avoidance of over-watering and over-fertilization. She continues that conservative additions of nitrogen or organic material increase mycorrhizal infectivity; warm temperatures favor mycorrhizal colonization; and mild drought, nutrient deficiency, the reduction of pesticide use and tilling, and an increase in the diversity of plant material promote increased numbers and biodiversity of mycorrhizal species.

 

Mycorrhizal Amendments

Mycorrhizal amendments are marketed and available for sale in various liquid and powdered forms in addition to being present in some fertilizer blends. Should we spend our money buying these products, and our time in applying them? Chalker-Scott reports that scientific studies have found no significant value in the addition of packaged mycorrhizae to healthy soils so their application is a waste of money and resources. She advocates instead that the best way to cultivate beneficial microbes is the addition of organic matter and “thoughtful, sustainable horticultural practices.”

 

Over-application of fertilizers, pesticides and fungicides detrimentally impact our soil system. The ‘less is more’ method of adding judicious amounts of nutrients to our soil only when needed, and gardening practices based on scientific studies are the best way to improve our soil and facilitate beneficial mycorrhizal activity. My research has convinced me to get that long over-due soil test.

Alfalfa Tea

Alfalfa tea is a great spring or fall potion that doesn’t interfere with normal seasonal processes.

Alfalfa tea releases a growth hormone that makes everything work better.

Just add 10 to 12 cups of alfalfa meal or pellets to a 32-gallon plastic garbage can (with a lid), add water, stir and steep for four or five days, stirring occasionally.

You may also “fortify” with 2 cups of Epsom salts, 1/2 cup of Sequestrene® (chelated iron, now called Sprint 330) or your favorite trace element elixir. The tea will start to smell in about three days. Keep the lid ON.

Use about a gallon of mix on large rose bushes, 1/3 that much on mini’s. And keep the water going. When you get to the bottom of the barrel, add water to fill it up again!

One load of meal or pellets will brew up two barrels full, but add more fortifiers for the second barrel. You’ll see greener growth and stronger stems within a week!

 
Learn to Read the Leaves

Learn to Read the Leaves

Rita Perwich

Consulting Rosarian, San Diego Rose Society

Roses & You, June 2020

Unblemished lush green leaves are a good indication that our plants are thriving, well watered and happy. Leaf abnormalities, on the other hand, are often signals that our roses are under attack or in distress. Causes are varied and can be due to environmental problems, chemical toxicities, mineral deficiencies and fungal and viral pathogens. A plant will respond to these conditions with symptoms that include wilting, spotting, color irregularities or misshapen leaves. Pests leave telltale signs of their presence with damage such as distorted leaves, webbing and holes. Identify trouble by learning to read your roses’ leaves, and then take action when appropriate.

Environmental Problems

Yellow or Brown leaves can have several very diverse causes:

Yellow leaves that drop can be a sign that there is not enough oxygen in the soil. This is often caused by over watering or inadequate drainage. On container plants, make sure the drainage hole is not plugged, and in very clay soils, consider growing your roses in raised beds.

On the opposite spectrum, yellow, drooping and wilting leaves, or leaves with brown tips can mean that your plant needs more water.

Don’t panic if your otherwise healthy and vigorous plant has some yellow and brown leaves. It is normal for old leaves to turn yellow, then brown and drop.

Leaves that are Distorted and Deformed. Phytotoxicity is the toxic effect on a plant due to compounds such as pesticides, herbicides, metals and salts.

Needle-like shoots and leaves are an indication of glyphosate (Roundup) damage. Even the tiniest amount of spray drift can injure your roses.

Burnt or brown tips and blotches. Fertilizer burn or pesticide toxicity can show up as brown or burnt leaf tips or leaf edges, or blotches on the entire leaf surface. Nutrient toxicity, the accumulation of soluble salts in the soil, is common in the rose garden especially with constant use of synthetic fertilizers. In addition to tip and marginal browning of leaves, it can stunt plant growth by interfering with water availability in the root zone. Salts must be leached from the soil by deep watering. Always follow fertilizer and pesticide label directions, do not over-fertilize and water your roses before and after you apply fertilizer. Improve soil drainage and the overall health of your soil with the addition of organic fertilizers and mulches.

Common Nutritional Deficiencies

When a plant lacks a required nutrient for growth, symptoms include reduced shoot growth and leaf size, yellowing of leaf tissue due to a lack of chlorophyll or death of plant tissue. Our roses need the primary nutrients, nitrogen (N), phosphorus (P) and potassium (K). They also require three secondary elements, calcium, magnesium and sulfur, and trace amounts of the micronutrients, boron, chlorine, copper, iron, manganese, molybdenum, nickel and zinc. When you apply fertilizer, check that you are periodically using a product that includes all these essential elements for rose growth. Deficiencies of an individual nutrient can result either when there is an inadequate amount of a specific nutrient in the soil or it is unavailable to the plant often due to an incorrect soil pH. The ideal pH for roses is 6.5 If your soil tests too alkaline, sulphur or aluminum sulphate can be used to add acidity to the soil. The most common way to raise the pH is to add pulverized limestone to the soil.

The most common deficiencies in roses are nitrogen and iron.

Primary Element Deficiencies

Nitrogen Deficiency causes the leaves to have a uniform, light green to yellow-green color starting from the bottom of the plant. Leaves turn progressively more yellow. You may notice a reduction in leaf size, spindly stems and poor growth. Apply fertilizer with nitrogen, or amend the soil with blood meal, alfalfa and compost. A low pH can also cause nitrogen to be unavailable to the plant.

Phosphorus Deficiency may be indicated by leaves at the bottom of the bush turning a purplish color.

Potassium Deficiency shows in the older leaves first, with a yellowing and browning along the leaf margins. This deficiency may be one of the causes for the development of blind shoots.

Secondary Element Deficiencies

Magnesium Deficiency which is common in sandy soils is manifested first by older leaves which may cup down, be of reduced size or display chlorosis between the veins.

Sulphur Deficiency is suspected when leaves are light green with lighter-green veins.

Calcium Deficiency may be indicated when young leaves are distorted and older foliage become a dull green or curl down at the margins.

Some Micronutrient Deficiencies

Iron is an immobile nutrient so an iron deficiency will be apparent in the upper newer leaves. The veins on the younger leaves will be green and the remainder of the leaf will be yellow. If the deficiency is not addressed, the youngest leaves, including the veins, become very pale yellow and very small. Apply iron in chelated form which is more readily available for uptake and may be applied to either the soil or foliage. The leaf symptoms can also indicate an alkaline pH which binds the iron in a form that the plant cannot absorb.

Manganese Deficiency can cause interveinal chlorosis in the leaves and a netted appearance.

Molybdenum Deficiency may be indicated when the youngest growth shows wilting and there is tip scorching on the leaves.

Zinc Deficiency may be suggested by malformed and distorted new growth such as twisting of leaves or leaves that form a rosette.

Copper Deficiency may be the cause of young leaves developing light edges.

Boron Deficiency is possible when new growth ceases or withers, and when leaves do not develop or are distorted.

Fungal Diseases

Rose varieties vary greatly in resistance. Do your research and buy resistant roses. Lessen fungal disease by planting in the sun, spacing properly, pruning annually and maintaining a clean garden.

Powdery mildew can be identified by a white talcum-powder-like growth on the top and bottom of the leaves and stems. Plants with glossy leaves are often less susceptible to mildew. A high-pressure spray of water will remove mildew spores that haven’t imbedded themselves into the leaf but do this early in the day to prevent water-initiated rust and black spot.

Black Spot infected leaves are distinctive because the spots have feathery margins on the upper side of leaves. The affected leaves must be bagged up and removed to the trash.

Rust is very prevalent in cool, moist weather and can be a problem in coastal areas and in inland areas in wet years. The rust colored powdery pustules are on the undersides of leaves. Avoid overhead watering and dispose of all rust affected leaves on the plants and those that have fallen off.

Anthracnose has red, brown or purple spots that darken with age. This fungal disease does not seem to affect the vigor of the bush but cut out affected leaves.

Downy Mildew has angular purple, red, or brown spots that appear between veins on leaves and then become yellow and drop. This fungal disease requires moist, humid conditions to develop, and infected leaves and stems must be removed from the garden immediately.

Viruses

Rose Mosaic Virus can cause yellow zigzag patterns, splotching, mosaics, line patterns and dark green spots or streaks. The problem largely is unsightly and may possibly decrease plant vigor. The virus infects roses through the propagation of plants and is not vectored by insects.

Rose Rosette Disease New shoots will be bright red and deformed, leaves are obviously abnormal and very narrow. The virus is transmitted by the eriophyid mite. Plants suspected of RRD must be removed, including roots, and destroyed.

Insect and Mite Damage

Leaf-Sucking Pests:

Wrinkled New Foliage. Aphids love succulent tender new growth and can distort the new foliage. Knock aphids off with a forceful spray of water.

Black Sooty Mold. Copious amounts of honeydew secreted by sucking insects can result in the growth of sooty mold which blackens the leaves. Control ant populations which protect sucking pests from insect predators.

Misshapen, Distorted, Bronzed New Foliage. Chilli thrips attack fresh new foliage as well as buds. Look for bronzing on the underside of new misshapen foliage. This is a very hard pest to control. You must cut out and bag all new growth and may need to spray with Spinosad.

Stippled Leaves, Webbed Foliage. Spider mites are hard to see but cause leaves to be stippled or bleached. There is often a fine webbing on the underside of leaves. Defoliation can occur especially in hot weather. Control with forceful jets of water directed to the underside of leaves three to four times a week.

Leaf-Chewing Pests:

Skeletonized Leaves. Rose slugs look like small green caterpillars and feed on the underside of the leaf. Squish them with your fingers or remove the leaves. B.t. will not eradicate rose slugs as they are sawfly larvae and not caterpillars.

Leaves with large irregular-shaped holes. The brown fuller rose beetles chew foliage and flowers at night leaving notched or ragged edges. Drop the beetles in a bucket of soapy water.

Leaves with semi-circular holes. Leaf-cutter bees cut these holes in leaves to line their nests. Bees are important pollinators so take no action other than to admire their precision. .

Leaves rolled and tied in webs and leaves with irregular holes. The rose budworm and other caterpillars chew holes and some may tie leaves with silk. Hand-pick them and clip rolled leaves. You can spray with Bacillus thuringiensis (B.t.) which does not harm our beneficial insects, spiders or birds.

Leaves devoured. Grasshoppers chew leaves (and flower petals) and you should strive to catch them but you have to be fast!

Learn to read the leaves because healthy leaves guarantee beautiful blooms.

Rose Roots Love Humic Acid

Norma Boswell

Master Rosarian, Tri-City Rose Society

Roses & You, June 2020

In 2020, if you want to place a sweet treat at your roses’ feet, add humic and/or fulvic acid to the soil (and let earthworms create some for you). These acids are not fertilizers. They are wonder-working soil strengtheners that remain after plant matter has decomposed in a special place like a peat bog, your very own compost pile, or the intestines of earthworms. Humic and fulvic acid improve the soil in many ways: strengthening biological activity, increasing water retention, helping chlorophyll synthesis and aiding nutrient uptake. Humic acid can chelate micronutrients. Chelation breaks ionic bonds and increases micronutrients’ availability in the soil. Better soil health means better root growth. Better root growth leads to stronger, more beautiful roses.

You can, of course, ask your favorite local nursery whether they sell humic acid. An online source is www.spray-n-grow.com. Their bag of Earthworm Castings is 100% organic and contains 1% nitrogen, 0% phosphate and 0% potash. Spray-N-Grow also sells a kit of ten soil tests for $19.95. These tests reveal pH and status of nitrogen, phosphorus, and potassium.

Last year I was keen on buying bags and boxes containing mycorrhizae and digging them into the dirt. Mycorrhizae are fungi that develop a symbiotic relationship with plant roots. The roots provide mycorrhizae with food, and the long strands of mycelium created by mycorrhizae bring water and nutrients to the plants. At least two problems or doubts have recently come to light about mycorrhizae: (1) the exact kind of mycorrhizae that work best with roses is not clear, and (2) the main nutrient a plant gains from mycorrhizae is phosphorus.

Your rose soil may already have enough phosphorus. When a plant has plenty of phosphorus, its roots won’t encourage mycorrhizal development. If you do a soil test, you can discover your soil’s wealth or scarcity of phosphorus. Phosphorus tends to stay in the dirt for a long time (unlike nitrogen, which depletes quickly and needs to be replaced after the roses have bloomed). If your soil has a wealth of phosphorus, it could be a waste of money and effort to fertilize with more, which tends to cripple the mycorrhizal network. You might want to focus on humic/fulvic acid instead.

My container of Soil Moist Mycorrhizae Container Mix Plus (www.soilmoist.com) adds several species of mycorrhizae fungi and bacteria that grow naturally in undisturbed soils. My box of Whitney Farms’ Life Link Rose & Flower Food from a few years ago contains both ecto and endo mycorrhizae, as well as 4% nitrogen, 6% phosphate and 2% potash. Its fertilizers are derived from dried poultry manure, bone meal, sulfate of potash, alfalfa meal, feather meal and kelp meal.

SOIL TEXTURE IS IMPORTANT

Check the soil for drainage and soil texture. Soil should be “friable” (loose and crumbly). About 50% of the soil should be air and water. Roots grow well in friable soil but not compacted (smashed by foot traffic) or waterlogged (not well drained, drowning rose roots). Healthy soil provides space for many beneficial creatures to flourish, including microbes and earthworms.

A good way to improve soil texture is to add compost. Compost consists of naturally decomposed organic material which adds carbon and nitrogen to the soil. Use your own compost, or buy bags of Dr. Earth compost from Fred Meyer or your favorite local nursery. The best product will be dark brown or black, moist but not soggy, have no recognizable wood, and give off no smell of ammonia or sulfur.

Earthworms will do a lot of texture and soil enrichment work for you. They can travel 3-4 feet in the dirt both vertically and horizontally. They ingest what they find, and excrete humus. The soil is efficiently aerated as they move.

PRODUCTS MUST HELP, NEVER HARM

Protecting our environment is paramount. What we choose to spray on our roses, and incorporate into their soil, must allow creatures that are beneficial to flourish. Read product labels. If contents can harm bees or kill earthworms, don’t use those products. Treat the insects that pollinate our crops, and the creatures that keep our soil workable, with wisdom and kindness. We and those we love will reap the rewards.

The Value of Alfalfa

My first memory of the word “alfalfa” will probably date me, since the first alfalfa that I remember was “Alfalfa” from the “Spanky and Our Gang” comedies. Alfalfa was a tall and lanky youngster with a freckled face and a wisp of hair that stood straight up at the back of his head. He was not too bright and his pants were too short, but his heart was usually in the right place. When we started growing roses in the 1990s, I learned about the other alfalfa – the food for rabbits and roses.

Alfalfa (Medicago sativa) is a member of the pea or legume family and is native to western Asia and eastern Mediterranean regions. The first record of alfalfa was in a book written by the Emperor of China in 2939 BC. The Greeks cultivated alfalfa starting around 500 BC for animal food and for some medicinal applications. Arab tribes named the plant “alfalfa”, which means “father of all foods”. Now alfalfa is widely grown and provides an important food source for many animals including horses, cows, rabbits and other domestic animals.

Why is alfalfa good for roses? As a fertilizer, alfalfa is 5-1-2, providing a good source of nitrogen, calcium, iron, magnesium, phosphorus, zinc, vitamins (A, D, B1, B6, E, K and U) and triaconatol, which is a fatty acid growth stimulant. Because of these beneficial components, alfalfa can provide roses many of the substances that they need to grow as well as stimulating growth.

Alfalfa can be used in many ways. Alfalfa meal can be worked into the soil around rose bushes. Normally one cupful per large rose bush and about one-half cup for miniatures is recommended. Alfalfa meal is also contained in many commercial organic products (e.g. Mills Magic Mix) because of its beneficial components. Alfalfa pellets can be used instead of the meal by again working the pellets into the soil around roses. The pellets will soon break down with watering or by rain to slowly release the trace minerals, triaconatol, and other important nutrients. Alfalfa pellets come in many sizes, depending on the animal for which they were intended. Alfalfa pellets for horse feed are much larger than similar pellets for rabbits. I usually buy pelleted rabbit feed that contains alfalfa for this purpose, as well as for making “tea”.

Alfalfa “tea” is another good way to provide the nutrients contained in alfalfa to the rose bush. In essence, by making a “tea” you are extracting the nutrients from the alfalfa product (meal or pellet) with water, much as you extract your tea bag to make a cup of Earl Grey or Constant Comment. To make alfalfa tea, put about eight to ten cups of alfalfa meal or pellets into a 30 gallon plastic garbage can, almost fill the can with water, cover and let bake in the sun for three to five days. Stir daily to make sure that the extraction process is well underway and to disperse any organic matter that has risen to the top of the water.

Eventually, the water extract will take on an orange color and the fibrous organic material will settle on the bottom of the garbage can. Now you are almost ready to give the roses a drink of your “tea”. Since I usually make alfalfa tea in the early and late summer, the water often gets very hot in the covered garbage can. For that reason, I try to put out the tea early in the morning.

But if I have to put out the tea after work, then filling the garbage can to near the top with the cool water from the hydrant helps cool down the tea and prevents damaging tender roots. I learned this lesson the hard way, by filling the garbage can up all the way at the beginning and burning some roots on my bushes when I applied the tea in the late afternoon without adding cooler water first. Now, I always leave room to add 5 or more gallons of fresh water to fill the can and cool the contents before applying morning or afternoon.

You can also fortify your alfalfa tea by adding additional ingredients before serving your tea. Water-soluble fertilizers, fish emulsion, and/or Epsom salts can be mixed with your tea to fortify the brew. Simply use the normal amount you would use in a regular fertilizer concoction or a little less to create the ‘drink of champion roses’! As with a regular fertilization program, give a gallon of the tea to large roses and about one-half gallon to miniature and mini-flora roses. Be careful not to stir up the organic material on the bottom as you dip out the tea.

After you have served the tea to your roses, the garbage cans should still have most of the fibrous material and a few gallons of liquid left in the bottom of the can. You can refill the garbage can with water and get a second extraction a few days later. After applying the second extract to your roses, you will need to dispose of the fibrous material. Some rosarians work the fibrous material into the soil of the rose garden as a soil amendment. However, you can also apply the alfalfa tea or the fibrous remains to other flowers. Our perennials especially like the leftovers, so we use all of the material, extract and solids.

So, if you see me carrying bags of rabbit food out to my car, rest assured that I haven’t gotten an Easter Bunny. I’m headed home to make tea!

Howard Walters’ Thought for the Month: “The trouble with good advice is that it usually interferes with our plans.” From the February, 2002 American Rose magazine.

This is a 2007 Award of Merit article

American Rose Society