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Organic Perennial Gardening and Pest Control: Home

Roses, euphorbias and nasturtiums; photo courtesy of Flickr cc/Michael Coughlan

Plants are exposed to different types of environmental stress. Both gardeners and plants need to contend with drought, weeds and a host of other concerns. Sometimes, plants are attacked by outside factors such as pests and diseases. Or they may suffer from neglect or poor horticultural practices such as improper pruning, watering and fertilizing, to name just a few.

In the urban environment one of the biggest challenges is the quality of the soil. Compaction is a common problem. Due to construction, foot traffic and other causes, soil often does not have proper drainage and is lacking in the rich, organic matter that is essential for healthy plants. Amending the soil and working from the ground up is one of the  most important ways of ensuring healthy plants.

Good Horticultural Practices in a Nutshell

  1. Plant on overcast days. Hot sun may stress the plants. Water your plants a day before planting (in the pot) and then water well immediately following planting. If the plant is pot bound, tease out the root ball.
  2. Do not bury the crown of the plant (the point where the roots and the shoots meet). Most perennials and shrubs should be planted at soil level.
  3. Water plants until they get established. Perennials need to be nursed along for the first year, while larger trees and shrubs require several years of care. Good watering practices are an inch a week, which translates roughly into ½ gallon per square foot,once a week (sometimes twice a week in the intense heat of mid-summer). Water in the morning so that foliage has a chance to dry.
  4. Proper spacing of plants provides room for healthy root growth and good air circulation. Thin your plants as they grow. Over-congestion leads to disease problems. Good garden hygiene is important.
  5. Practice good soil management. Incorporate organic material into your beds on an annual basis and ensure good drainage. Mulch 2 to 3 inches in the spring once the soil has warmed to suppress weeds and retain moisture. Get a soil test before undertaking extensive work on your soil or when considering whether you need to change the pH.
  6. Deadhead certain plants to encourage repeat flowering. Stake your plants before they flop over.
  7. Remove rotting or damaged foliage immediately so the problem does not spread. If you are working with diseased plants, disinfect your pruner with rubbing alcohol.
  8. Pay attention to site analysis and plant selection. The wrong placement of a plant means high maintenance. Lavender, for example, loves full sun and good drainage. Plant it standing on its own or at the front of the border, rather than in a mixed bed where it gets water-logged and shaded. Plant moisture-loving plants where water collects in your garden, rather than planting them on a slope.      
  9. Select good plant partners and good companion plants. Group plants with similar growth requirements together and choose plants that will not out-compete one another. Some companion plants help protect other plants from pest and diseases.
  10. Diversity is an important component of a healthy garden. Diversity creates physical barriers so that specific diseases and pest do not spread so rapidly. Diversity (particularly in the form of native plants) attracts wildlife and beneficial insects that help keep a healthy and balanced environment.
Lavenders, like this Lavandula x intermedia 'Provence', like full sun and good drainage
Lavenders, like this Lavandula x intermedia 'Provence', like full sun and good drainage

Alternative Ways of Thinking about the Garden: Bio-friendly Approaches to Gardening

There are a number of good reasons to encourage organic or bio-friendly approaches to gardening. The use of pesticides in the garden poses important concerns such as potential health risks and the possibility of contaminating ground water. There are many friendlier alternatives. They may not be as fast-acting as synthetic means, but they are more supportive of the environment. They allow beneficial insects to thrive in the garden and, with patience and repeated application, they can be just as effective.

The best way to tackle problems in the garden is prevention. Adopt good horticultural practices and select disease-resistant varieties. Select native plants and non-natives that are well adapted to your local conditions. Look for plants that are low maintenance, non-invasive and have good ornamental value.

Practical Tips

  1. To test drainage, dig a 1 x 1 x 1 foot hole and fill it with water. After it has drained, fill it again and time the drainage. Average garden soil drains at the rate of 1 inch per hour.
  2. Amend sandy soil with organic matter such as compost (either your own or one of the many commercial brands). Amend heavy clay with organic matter or improve drainage by adding gypsum (follow directions on label). Amend the entire planting area, not just the hole, otherwise you may create a sinkhole or an artificial environment where the roots are not encouraged to grow into the surrounding area. Raised beds also work in areas with poor drainage.
  3. The soil pH helps plants absorb nutrients properly. The optimal pH for most perennials is between 5.5 and 7. Add lime to raise pH and elemental sulfur or pelletized sulfur to lower pH. Always get a soil test.
  4. Fertilize repeat flowering plants immediately after the first flush to give them energy for subsequent blooms. Do not fertilize when they are dry or wilting - you will burn them. Instead, rehydrate first before feeding. Avoid over-feeding plants that like to be grown lean. Many drought tolerant plants such as yarrow, Russian sage and lavender fall into this category. Over-fertilizing plants results in excessive leaf growth that attracts pests.
  5. Removing infected foliage is sometimes all you need to do to contain a problem. Good sanitation for fungal problem such as leaf streak on day lilies is all you need.
  6. Remove aphids from plants by giving them a strong blast of water from your hose. Repeat for good control. Encourage beneficial insects, such as ladybugs that eat pests by planting flowers that are attractive to them such as yarrrow, lovage, zinnias and gem marigolds.
  7. Insecticidal soap and horticultural oil are natural alternatives to chemicals. If you are concerned about the phytotoxicity (causing damage such as leaf burn), then spray a small areas of the plant and wait at least 24 hours. Always read the label. Use vegetable based oil and not petroleum based oils on vegetables.
  8. Hot pepper sauce (see products such as Hot Pepper Wax) help keep rabbits away from your vegetable garden. Homemade remedies of pepper and garlic work just as well. Effective deer repellents contain peppermint, garlic and other natural oils.
  9. Use corn gluten meal as a natural pre-emergent herbicide to control weeds on your lawn.
  10. Prevent slugs from devouring your hostas by surrounding your plants with used coffee grounds (make sure it is caffeinated grounds),  diatomaceous earth or grapefruit rinds (that function as traps). Sluggo® (iron phosphate) is a good commercial alternative. Hostas with thick, puckered leaves are less susceptible to attack.
  11. Thin out plants such as phlox and beebalm that are susceptible to powdery mildew. Proper spacing and good air circulation is important. Home remedies for mildew contain baking soda and insecticidal soap. Add fermented salmon plant food from Coast of Maine to increase the fungicidal properties and help keep pests away. Environmentally friendly products such as Green Cure®and Safer Brand® Garden Fungicide combat powdery mildew on phlox as well as being suitable for black spot on roses. Choose disease-resistant varieties: Phlox paniculata 'David', 'Delta Snow', 'Rosalinde', 'Robert Poore', 'Starfire', and 'Speed Limit', Monarda 'Marshall's Delight', 'Claire Grace', 'Jacob Kline', 'Petit Delight', 'Vintage Wine' and 'Raspberry Wine'.
  12. Two environmentally friendly insecticides available to vegetable gardeners and general gardeners alike are products that come from naturally occuring bacteria: spinosad (see products such as Entrust®) and Bt, Bacillus thuringiensis, (see products such as Dipel®). Different strains of Bt act against caterpillars, flies and beetles, while spinosad targets aphids, whiteflies, thrips, leaf hoppers, cucumber beetles and a whole host of pests.
  13. Nematodes are more readily available on the market these days and effective on many pest problems including Japanese beetles. Some companies such as BASF specialize in these beneficial nematode products.
  14. Research Web sites such as Gardens Alive, Arbico Organics and Johnny's Selected Seeds for natural alternatives to pest and disease control.

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