Wednesday, December 06, 2006

Should I put fish in my pond?

Fish add movement and character to any pond, and they are an important component in a healthy aquatic ecosystem. They also eliminate mosquitoes and other insects that breed in water. Many fish species also eat aquatic plants, however, so it is important to keep their numbers at a reasonable level. Many aquatic gardeners keep ornamental carp known as koi in their ponds. These fish are available in a myriad of colors and patterns and can live for a very long time and grow quite large. Goldfish are very adaptable and can survive the winter in your pond if it does not freeze to the bottom and a portion of the water surface is kept free of ice to allow for gas exchange.

If you choose to keep fish in your pond, make sure they don't have the opportunity to escape to natural waterways in your neighborhood where they can compete with and displace native fish species.

What can I do to keep algae out of my pond?

The algae is growing because the nutrients are available to support its growth. A small amount of algae is good for the aquatic garden since it absorbs excess nutrients in the water, helping to keep it pure. Uncontrolled algal growth depletes oxygen in the water and makes the water inhospitable for the fish.

Make sure that you have not overstocked your pond with fish. Also make sure that you are not overfeeding your fish. Uneaten food is source of nutrients that translates into algal growth, and a large population of fish produces a large amount of nutrients when they excrete waste products. A pond biofilter can help remove excess nutrients and keep the water clear. You can also add water to the pond periodically to dilute nutrients if you have an overflow system that can drain excess water out of the pond. Barley straw discourages the growth of certain types of algae. Pond supply firms sell barley straw products that can be submerged in your pond. Dyes are available that can be added to the water. The black material absorbs the sun's light energy and deprives the algae of the light it needs to carry out photosynthesis and survive. Dye products have the added advantages of protecting your fish from predators and concealing plumbing and pots in your pond.

Many aquatic plant gardeners are tempted to drain the pond, clean it, and start over with fresh water when confronted with algae. This is usually counterproductive since the excess nutrients that cause algae to grow build rapidly in the fresh water. Frequent water changes and cleaning can make for drastic changes in pond pH and are stressful for fish and other aquatic life. Only drain and clean your pond when a substantial layer of decaying organic matter has accumulated at the bottom.

Can I keep my plants in the pond during the winter?

That depends on which plants you are growing. Some aquatic plants are perfectly hardy and can spend the winter in the pond. Hardy water lilies and lotus can simply be moved to a lower depth in the pond. Hardy plants such as cattails, water iris, and rushes can stay near the water's surface where they normally grow. Tropical plants such as tropical water lilies, cannas, and papyrus cannot even tolerate cold water, so they must be kept in a greenhouse over the winter or they must be started from new divisions every year.

Can I grow any canna in my pool?

Cannas are native to moist areas and many do quite well if grown in water, as long as they are not submerged too deeply. The cannas in the pool at the U.S. National Arboretum are varieties of Canna glauca or hybrids between Canna glauca and other canna species. They may also be grown in bog plantings where the soil is constantly saturated. Garden cannas are surprisingly adaptable to wet conditions and some may be grown in water if temperatures are warm. The rhizomes of all cannas rot in cold, saturated soil, so they cannot live over the winter in the aquatic garden.

How should I prune my roses?

Prune your roses lightly in autumn, removing canes long enough to be whipped by winter winds and those canes with signs of disease. Pruning to remove remaining dead, diseased, and damaged canes is done in early to mid-March just before growth starts. Species and climbing roses are pruned by removing entire canes all the way to the ground to encourage an open, vase-shaped habit. The rest of the roses get pruned to knee height at an outward facing bud. You can do some light pruning to shape the plants during the summer as needed.

What can I do about black spot on my roses?

Roses are not the easiest plants to grow in the Washington, D.C. area. Our climate is perfect for the development of black spot, a fungus that can defoliate and weaken plants if not kept in check. Fortunately, antique, heritage, and species roses are generally more resistant to diseases and pests than hybrid tea roses. When control measures are needed, the Arboretum practices Integrated Pest Management (IPM) to control pests and diseases. The practice combines planting disease resistant varieties, promoting proper cultural techniques, and careful monitoring of pests combined with spraying, natural control methods, and tolerance of minor amounts of damage. To minimize black spot problems and limit the amount of spraying you need to do in your own rose garden, follow these tips:

* Promote air circulation and light penetration. Prune trees and hedges surrounding the rose garden low so that sunlight and breezes can quickly dry the foliage after morning dew or rain. Keep companion plantings at a distance to allow maximum exposure of the rose foliage to sunshine and air.
* Eliminate overhead irrigation. Water the soil with a soaker hose and keep the leaves dry. Black spot spores need water on the leaf surface to germinate.
* Prune cankered canes. Cankered stems bear black, dead areas that harbor the fungus over the winter. Prune them out, preserving more vigorous healthy canes, to prevent infection of spring foliage.
* Apply lime sulfur just before bud break in spring. This treatment delays the onset of black spot and powdery mildew infections for several weeks, even if weather is favorable for infection.
* Apply a fungicide based on neem seed extract beginning when leaves are fully expanded. Neem products are not as toxic as conventional fungicides and have the added benefit of controlling many rose insect and mite pests. They only work to prevent new infections, so spraying must be done on a weekly basis as long as weather is humid or wet.
* Apply conventional fungicides as a last resort. If the weather is dry in early summer, and you have applied neem every week, you may not have a black spot problem at all. But if you miss an application, or daily rain and dew create ideal fungal infection and growth conditions, you may need to use a conventional fungicide. Use a fungicide containing chlorthalonil, thiophanate methyl, or propiconazole. It's best to rotate different fungicides, never using the same one two times in a row, to prevent the fungus from developing resistance to the fungicides.
* Tolerate some damage, especially late in the season. Heritage and antique roses generally bloom in late spring and bloom only sporadically throughout the rest of the season. In July and August, with the flowers gone, the plants attract little attention and some black spot can be tolerated without permanent harm to the plants.

Basic Plant Requirements

Anyone interested in gardening has one question in mind when choosing a new plant: Will it thrive in my garden?

Many factors come into play to determine whether or not a plant will perform well for you. Each kind of plant has its own needs and requirements. Some plants, like the dandelion, are tolerant of a wide variety of conditions, while others, such as the pink ladyslipper orchid, have very exacting requirements. Before you spend the time, effort, and money attempting to grow a new plant in your garden, it is best to do some research to learn something about the conditions that the plant needs to grow properly.

Here is a brief description of some of the environmental parameters that influence plant growth:

Daylength is usually the most critical factor in regulating vegetative growth, flower initiation and development, and the induction of dormancy. Plants utilize daylength as a cue to promote their growth in spring and prepare them for the cold weather. Many plants require specific daylength conditions to initiate flowers.

Light is the energy source for plants. Cloudy, rainy days or the shade cast by nearby plants and structures can significantly reduce the amount of light available. Shade adapted plants cannot tolerate the bright light of full sun. Plants survive only where the amount is within a range they can tolerate.

Plants grow best within an optimum range of temperatures; and the range may be wide for some species, narrow for others. Plants survive only where temperatures allow them to carry on life-sustaining chemical reactions.


Plants differ in their ability to survive cold temperatures. Some tropical plants are injured by temperatures below 60°F. Arctic species can tolerate temperatures well below zero. The ability of a plant to withstand cold is a function of the degree of dormancy present in the plant, its water status, and general health. Exposure to wind and bright sunlight or rapidly changing temperatures can also compromise a plant's cold tolerance.

Heat tolerance varies widely from species to species. Many plants that naturally grow in arid tropical regions are naturally very heat tolerant, while subarctic plants and alpine plants show very little tolerance for heat. High night temperatures are often the most limiting factor for many plants.

Different plants have different water needs. Some tolerate drought during the summer but need winter rains. Others need a consistent supply of moisture to grow well. Careful attention to the need for supplemental water can help you select plants that need a minimum of irrigation to perform well in your garden. If you have poorly drained, chronically wet soil, you can select lovely garden plants that naturally grow in bogs, fens, and other wet places.

The ability of plant roots to take up certain nutrients depends on the pH, which is a measure of the acidity or alkalinity of your soil. Most plants grow best in soils that have a pH near 7.0. Most ericaceous plants such as azaleas and blueberries need acid soils with pH below 6.0 to grow well. Lime can be used to raise pH and materials containing sulfates such as aluminum sulfate and iron sulfate can be used to lower pH. The solubility of many trace elements is controlled by pH, and only the soluble forms of these important micronutrients can be used by plants. Iron is not very soluble at high pH and iron chlorosis is often present in high-pH soils, even if they contain abundant iron.