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Plant Tips

Spring culture tips

Here are a few suggestions from the Mason Dixon Chapter to aid with the Spring care of your rhododendrons:

  • Avoid walking around your rhodos and azaleas when the soil is wet...and never compact the soil at the drip line of the branches.
  • Pruning: some good hints:

    • when removing dead wood...dip or spray your pruning shears with alcohol or 10% Clorox between every cut.
    • look for borer holes, cut back until the stems are whole.
    • if severe pruning is necessary for shaping the very early rhodos or azaleas, you can cut them back immediately after flowering.


  • Planting hints:

    • Spring planting is OK, but less desirable than in the Fall.  You need to be willing to coddle plants through the summer...this means, mulch, water, shade, and generally protecting them!
    • container-grown plants need to have their root balls loosened and spread out into the surrounding soil in the planting hole before filling.
    • all plants need to be mulched.
    • a few rocks on top can help hold things in place until the roots anchor the plant firmly.
    • if the site is unprotected by trees or shrubs, make a temporary windbreak of burlap stretched around stakes.
    • throughout the garden replenish the mulch to help plants retain moisture during the summer.

A slice of bog in your garden?

From the Rhododendron Society of Canada, Toronto Region, comes the most interesting information for Spring.

This is the time of the year when some of you will be picking up bales of chunky peat moss for your rhododendron garden.  Peat grows in bogs.  The word "bog" brings to mind a smelly, uninviting quagmire swarming with hungry mosquitoes. on and you will see that peat bogs are interesting places that don't fit the common image.

Bogs are found in cool, moist regions once covered by continental glaciers, some 12,000 years ago.  Canada has more bog land than any other country; those adjacent to Hudson Bay are several times larger than Lake Superior or Nova Scotia.

Bog facts...

Although a bog is soggy and wet, it is not odorous.  A multicolored carpet of sphagnum forms the surface of the bog.  This moss converts rainwater into an acid, discouraging the mosquito from breeding in the bog itself.  The mosquitoes breed farther way on slightly higher wet terrain surrounding the bog.  But, the acid of the bog does more...

A key role in formation of the bogs is played by the sphagnum moss. The carpet of moss may be one to two meters or more thick...and be more than 400 to 500 years old.  As the sphagnum on the surface grows upward upon itself, the older layers die and accumulate, forming peat.  In forests, dead material is incorporated into the soil by fungi and bacteria.  The sphagnum, however, releases organic acids (such as brown-colored tannic acid) which inhibit growth of bacteria and fungi.  Dead moss remains intact and gradually compresses under its own weight.  Thus, the surface of the living sphagnum gradually rises, resting on top of the previous now browned-off generations of dead sphagnum moss.  This mass of brown peat moss is the stuff dug up and sold to you as chunky or powdered peat moss with a pH ranging from 4 to 5, really acid stuff!

Reason for peat moss being spongy

Under a hand lens or microscope, one can see that a network of large and small cells gives the plant a water-holding capacity of more than 16 times its weight.  This characteristic allows sphagnum moss to draw up the water table as it grows upward.

Without any bacteria and fungi...because of the acid...peat moss is sterile.  During World War I it was used as a substitute for surgical wound dressings.  Imagine the surprise of Danish peat moss diggers when they found a human body near the bottom of a bog.  Scientists believe the body to be 2000 years old.  The body, and even the leather belt and cap, were well preserved in the brown acidic water due to absence of oxygen and bacteria.

Rhododendrons like the acidic sphagnum peat moss because this material will assist you in preparing a growing medium for rhododendrons with a range of pH between 5 to 6, as well as providing a water and nutrient-holding medium.

Although sphagnum peat areas are abundant in Canada, many of these areas are inaccessible, and they need long periods of time to least 400 years or more.  Such time periods are several times longer than Canada's existence as a country...and such periods of time to form peat bogs equal that of our 2000-year-old Western civilization.  The point is: sphagnum peat is a slowly-renewable resource.  Overuse as a horticultural soil amendment can easily lead to the depletion of the accessible peat areas and drive up the price...while leaving gouged out areas in the ground.  One can help by using as much composted organic materials...leaves, newspapers, cardboard boxes, and one can get, in combination with the very plentiful sulphur materials.  Wise use of peat is neat!

Adapted from a Pacific Rim National Park brochure and modified for consumption by rhododendron gardeners.


"Dirty" speech leads to garden success...

The Eugene Chapter, Oregon, received some very basic guidelines for "dirt" and how to take advantage of this very basic ingredient from Larry Landauer, owner of Floraland Nursery, Forest Grove, Oregon, who gets down to earth at his nursery and in his talks.  Listen to some of his advice for a more beautiful, healthful garden.  He guarantees you'll reap rich rewards.

Four purposes of dirt:

  • supports the plant,
  • serves as a reservoir of minerals,
  • provides supplies of air, and
  • provides supplies of water.

Have problems with your plants?  The cause: plant is either too wet or too dry!  And...all other problems are related, says Larry.

He states that the soil at Floraland Nursery is "so unique" that it has its own designation in the soil categories of Oregon: "Aurora Muck".  What's that?  He found that it has "nothing organic" in it and holds water very, very well.  It has the consistency of pudding!

How to fix your "not too good soil":

  • avoid using peat moss or sand,
  • fir bark is good...but it doesn't last too long,
  • use sawdust cautiously.  It was great at first but it turned into the most amazing pudding kind of stuff.

Evaluate plant's health:

  • a plant with long, bare stems may have dropped the leaves on that stem due to a lack of nutrients from fertilizer,
  • use soil-testing materials, finding out the soil pH.  Avoid testing in too wet or too dry soil...the readings could be way off,
  • always make sure you know what is in your soil before starting to make changes
  • for rhododendrons and other plants, a pH soil-test reading on the acid a problem.  Solution to the Larry points out...a 5 lb-bag of ammonium nitrate per 1000 sq. ft. of bark dust, for each inch of dust added.

Those time-release pills...

Larry directs attention to those "little pills" you see in purchased pots or flats of new plants, emphasizing that all of them don't work the same way.  He urges gardeners to carefully time the type of time release to the stage of growth that their target plant is currently experiencing.  And, the different brands of time-release products work with different time-release cycles.  Release cycles may be water activated or temperature activated.

He emphasizes that rhododendrons "never do get completely dormant."  He fertilizes in November, January, and March, and sometimes uses moisture meters to maintain correct garden levels.

For container mixes: He uses 60 percent fresh fir dust, 15 percent peat moss, 15 percent sawdust, and remainder, river sand...for weight.


Frost damage

Frost damage is a real concern for many, depending on the area in which you live.  Frost damage causes considerable damage to: leaves, stems, buds, and flowers.  Careful consideration should be given to the planting of tender varieties.

This is what happens if frost damage has occurred: the leaves will become distorted, curled, and often grow only on one side of the main vein.  Once leaves have been frost damaged their distortion will become less after new uninjured leaves begin to develop...if too unsightly...remove them.

Frost can also cause the bark of affected stems to split longitudinally near ground level, sometimes peeling away. This usually happens in early Fall or late Spring when the plant is not fully dormant. Often these symptoms are overlooked and the damage is only noticed at a much later date. If noticed fairly recently after the injury...and before the bark has had time to dry out...the area can be wrapped with galvanized wire or a non-sticky wrapping. Ensure that the wire is removed, if the union is successful, and check the wrapping monthly. Caution: do not use duct tape.

(From the North Island Chapter Newsletter)


Simple tips for small measures

Have you often wondered about measurements?  Especially small measures?  Have a solution for you.

Use your cookbook!  Remembering that...

  • a teaspoon = 60 drops
  • a tablespoon = 180 drops

So...if instructions call for 1 tsp per gallon of water, divide 60 by 16 to get about 4 drops.  Use eyedroppers to measure drops.


Efficient weed killer: vinegar!

Who would have ever dreamed that this liquid called "vinegar" can be used as an efficient weed-killer.  But there's more to it than the familiar table vinegar.  It's 20% acetic acid.  Here's what happens:

  • spray directly on the plants or apply as drench to the soil.
  • spraying strips off the waxy, protective coating on the foliage and makes plants vulnerable to desiccation.
  • vinegar concentrates sprayed onto soil work by lowering the soil pH to a level where plants can't survive.

This acidifying effect can last up to a year, depending on soil type and weather.  Once the soil pH is lowered, taproots will eventually starve...but might have one fast flush of growth from nutrients stored in the roots.

  • once plants are dead...which may take up to six months...bring the soil pH back to neutral level by adding lime at a rate of 5 lbs. per 100 sq. ft., and add a 3 to 4 in. blanket of compost to restore microorganisms.
  • works best on warm dry days, temperature 65 F.
  • if used before watering or rain, it will wash off.
  • citrus oils, alone or combined with vinegar, are also very effective.
  • use for mixtures will kill anything they touch.  Be careful.
  • wear eye protection and gloves...don't expose any skin to the spray.
  • named products: eugenol (a clove and cinnamon oil compound), acetic acid, and
    citric acid as shown on the label.

(Source: Ann Lovejoy, Fine Gardening, #91)


Notes on fertilizing...

Allan Murray, Cowichan Chapter, has given talks and guidelines for successful fertilizing and recently wrote an informative article for the Chapter newsletter.  It's excellent and now we want to share these guidelines with the world.

The quality and quantity of the flowers on your rhododendrons next year depends greatly on what and when you feed them this year.  Nitrogen, phosphorus, and potassium are three elements that you need to keep plant growth in proper balance: in terms of growth, flower set, and leaf color.  A properly fertilized plant is hardier and can withstand more cold than one underfed.

the right elements...

Applied in the right amount:

Nitrogen: promotes normal growth and healthy green leaves.

Phosphorus: promotes root development and increases flower production...without ample phosphorus, the quality and quantity of blooms is reduced.

Potassium: has overall value to plants providing them with vigor and disease resistance. Rhododendrons without sufficient potassium will look unhealthy...and their appearance will disappoint you.

identify deficiencies...

You can easily identify deficiencies of these elements in rhododendrons with these symptoms:

Nitrogen: lighter leaves than normal for the variety, stunted growth, stalks too slender, few new side shoots.  On the other hand, too much nitrogen will burn the foliage, destroy the young feeder roots and force excessive vegetative growth.  Burn is generally at the ends and edges of leaves and will be on any area of the whole plant, not just the sunny side.  Give as much water as possible to wash the fertilizer out of the roots.

Phosphorus: foliage darker than normal, shoot growth retarded, sometimes a yellowing between the veins on the lower leaves, generally the leaf coloring is purplish, especially on the stalks.

Potassium: localized in older lower leaves; dead leaf margins and tips occur and the leaves appear mottled; yellowing beings at leaf margins and moves toward the center; finally the margins curl under and turn brown, older leaves usually drop.

get plant information before fertilizing

Before you begin to fertilize, Allan points out there are several important steps to take:

  • look for a soil pH of 4.5 to 5.5,
  • examine the previous year's growth, bud set, leave color, and size, and
  • note the position of the plant: sun/shade, water, especially overhead water.

This information will help you determine how much fertilizer your specific plants need.  For example: water use or rainfall will determine the amount of fertilizer needed; overhead and sprinkler systems may require more fertilizer applications per year as the water will wash away some of the fertilizer; drip or restricted water systems may reduce the number of fertilizer applications per season.

selection of chemical fertilizer

Chemical fertilizer comprises non-organic material, it is quick acting, and is usually cheaper and more convenient than organic fertilizer. Green Valley's 10-8-6 rhododendron fertilizer comprises:

10% nitrogen
8% phosphorus
6% potassium
5% magnesium
1.8% iron
6% sulphur and trace minerals

This fertilizer was developed by Tom Brown, head of the Geology Department at the University of British Columbia, and a member of the Vancouver Rhododendron Chapter.

Schedule dates to apply chemical fertilizer:

mid-March, first application
mid-April, second application
1st week in May, third application

Later fertilization is not recommended: soft succulent growth is the first to be damaged by a freeze; the plants need to be in a mature woody condition for when the cold weather arrives.  Sprinkle 3 to 4 oz per sq. yd. at the top drip line of the rhododendrons...taking care to avoid spills on the leaves. If left on, the fertilizer will burn the leaves.

organic fertilizer

Allan's organic fertilizer is made of once living materials or byproducts of things once living, e.g., blood meal, bone meal, manure, and/or compost.  It is slower than chemical fertilizer, but feeds longer. Organic fertilizers are ideal for rhododendrons from the standpoint of both nutrients and humus. it is made as follows (measure by volume):

4 parts alfalfa meal 1 part rock phosphate
4 parts canola meal 1 part bone meal
4 parts blood meal 1 part kelp meal
2 parts dolomite lime 1 part greensand

To apply an organic fertilizer: with its trace elements, the fertilizer will release slowly for two to three years, but should be applied each year for maximum benefits.  When to apply depends on the weather.  Generally speaking:

  • beginning of March: spread magnesium sulphate (Epsom Salts)
  • at the rate of 1/2 lb per 100 sq. ft.
  • mid-March: sprinkle organic fertilizer around the plant drip linet, 2-3 oz (by volume) per sq. yd

Keeping your rhodos happy!

All of us are most interested in finding new ways to keep our rhodos happy...all year round. Well, Norman Todd, North Island Chapter, who has had his own nursery for about 20 years and has more than 300 species and 900 hybrids in the garden.

These are some ways he has found to keep happy rhodos in your garden:

  • if rhodos reside in soil that is black, fertile, friable (i.e. means easily crumbled, reduced to powder!), and has the right amount of humus...the rhodos may never need fertilizer,
  • heavy winter rains can wash away he feeds his rhodos every two months starting in November and ending July 1,
  • fertilizer need is governed by soil temperature, and doubles with every temperature increases of 10 C,
  • plants that benefit from 30 milliliters of fertilizer in November could require double or triple that amount in May,
  • believes plants need extra nitrogen...uses the 10-8-6 formula developed at the University of British Columbia.

This formulation contains all 13 elements needed, and 50% of the nitrogen is offered as sulfur-coated urea, when is released over a long period.

Most common reason for yellowing of rhodo leaves is: shortage of nitrogen.  Solution: add fish fertilizer 5-2-3 or Miracid 30-10-10.

Yellowing can also indicate a shortage of magnesium.  Solution: use Epsom salts...15 milliliters to 4 liters of water. If this doesn't solve the problem, use chelated iron.

Should you prefer organic fertilizer, the following mix, developed by Alan & Liz Murray, Cowichan Chapter, is recommended:

  • 4 parts each of canola, alfalfa, and blood meal,
  • 2 parts dolomite lime,
  • 1 part each of rock phosphate, bone meal, kelp meal, and greensand.  Apply once a year, and mulch heavily with ground bark.

Note: Norman recommends, if changing to organic feeding, do it over time, overlap applications, as this mixture takes time to break down and release its nutrients.  Norman strives to make his rhodos happy and encourages you to do the same.  Simple enough.


Use for old shower curtains

Here's a significant use: old shower curtains make fine garden tarps, cover piles of compost or leaves, and for gathering weeds.  Time to start planning now.  Just think of the garage sales you can go to and buy the curtains for a song!


Removal of caterpillars...

The Nanaimo Chapter's newsletter had an interesting cartoon of a bird pulling a caterpillar out of the ground...and offered this advice.  You can wait for the birds or try the following:

  • Caterpillars are easily and legally knocked back by using Bt.  Bt is Bacillus thuringiensis, a naturally occurring bacteria that paralyses the stomach of caterpillars.  They stop eating as soon they ingest some of this material...and die of starvation a few days later.  It should be available at your local garden center.
  • Hint: Make sure it is this year's production. It doesn't store well over six months time.  Cover the leaves where they are eating  and the problem is solved for all caterpillars and loopers.

Healthy rhododendrons need healthy roots.

Have you wondered why your rhodos are not as healthy as you expected them to be?  You may not have considered four extremely important factors to have success.

Eileen Hoffman of the Nanaimo Chapter, Canada, replied to Richard White who asked a similar question...and she gave him the following guidelines.

First, that clump you bury in the ground and never see again...that clump is actually a mirror reflection of your plant.  Simple enough.  Growing healthy roots...grows healthy rhododendrons.  Second: consider the following:

Location: rhododendrons roots are surface feeders, developing a shallow root system.    Because rhododendron roots obtain much of their oxygen and water near ground level, do not plant too deep, providing them with adequate water.  This is achieved by digging a shallow hole and backfill hole with amended soil (soil mixed with mulch).  Place roots half way in hole, lightly cover the top of roots with mulch.  One nice point to having a shallow root system is they do transplant fairly easy.

Water/Drainage: rhododendrons roots love water.  They can sit in it when the temperatures are cool, but when it is hot and humid, they can develop root rot.  Some tips:

  • well-drained soil is the key,
  • amending your soil can be very inexpensive,
  • use materials such as, pine needles, fresh sawdust, or bark dust,
  • mix the mulch into your existing soil,
  • Planting on a hillside or slope also provides good drainage.

Not recommended: using fallen leaves because they can contain disease, but they do make a nice top covering in winter months.

Spacing: When planting consider spacing and these factors.  A quick and general rule is:

  • how tall the plant will be in 10 how far a part you want to plant the plant's center.
  • if the rhododendron will be 4 ft in 10 years, plant the centers (the stems) 4 ft a part.  You can stagger the plants for a more full look.

Fertilizing: Is it lunchtime yet?  Yes!  Rhododendrons roots get hungry, too!  Recommend feeding rhododendron roots as early as March, then a small dose every 4 to 6 weeks until mid-July.  Fertilizing after July can initiate Fall new growth that is susceptible to early frost.  You can purchase rhododendron/azalea food at your local garden supply store.


Something to share...dreams...what are they?

Dreams are the touchstone of our characters.
  --Henry David Thoreau


American Rhododendron Society
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