Centaurea bella ( Knapweed )

Characteristics

Cultivar:	n/a
Family:	Asteraceae
Size:	Height: 8 ft. to 12 ft. Width: 0 ft. to 0 ft.
Plant Category:	landscape, perennials, shrubs,
Plant Characteristics:	irregular growth habit, low maintenance, seed start,
Foliage Characteristics:	medium leaves, evergreen,
Foliage Color:	green,
Flower Characteristics:	long lasting, nodding, old fashioned/heritage, showy, unusual,
Flower Color:	pinks,
Tolerances:	deer, seashore,

Requirements

Bloomtime Range:	Early Summer to Late Summer
USDA Hardiness Zone:	4 to 8
AHS Heat Zone:	1 to 1
Light Range:	Sun to Full Sun
pH Range:	5.5 to 7.5
Soil Range:	Mostly Sand to Clay Loam
Water Range:	Dry to Normal

Plant Care

Fertilizing

How-to : Fertilization for Annuals and Perennials

Annuals and perennials may be fertilized using: 1.water-soluble, quick release fertilizers; 2. temperature controlled slow-release fertilizers; or 3. organic fertilizers such as fish emulsion. Water soluble fertilizers are generally used every two weeks during the growing season or per label instructions. Controlled, slow-release fertilizers are worked into the soil ususally only once during the growing season or per label directions. For organic fertilizers such as fish emulsion, follow label directions as they may vary per product.

Light

Conditions : Sun

Sun is defined as the continuous, direct, exposure to 6 hours (or more) of sunlight per day.

Conditions : Types of Pruning

Types of pruning include: pinching, thinning, shearing and rejuvenating.

Pinching is removing the stem tips of a young plant to promote branching. Doing this avoids the need for more severe pruning later on.

Thinning involves removing whole branches back to the trunk. This may be done to open up the interior of a plant to let more light in and to increase air circulation that can cut down on plant disease. The best way to begin thinning is to begin by removing dead or diseased wood.

Shearing is leveling the surface of a shrub using hand or electric shears. This is done to maintain the desired shape of a hedge or topiary.

Rejuvenating is removal of old branches or the overall reduction of the size of a shrub to restore its original form and size. It is recommended that you do not remove more than one third of a plant at a time. Remember to remove branches from the inside of the plant as well as the outside. When rejuvenating plants with canes, such as nandina, cut back canes at various heights so that plant will have a more natural look.

Conditions : Full Sun

Full Sun is defined as exposure to more than 6 hours of continuous, direct sun per day.

Watering

Tools : Watering Aides

No gardener depends 100% on natural rainfall. Even the most water conscious garden appreciates the proper hose, watering can or wand.

Watering Cans: Whether you choose plastic of galvanized makes no difference, but do look for generous capacity and a design that is balanced when filled with water. A 2 gallon can (which holds 18 lbs. of water) is preferred by most gardeners and is best suited for outdoor use. Indoor cans should be relatively smaller with narrower spouts and roses (the filter head).

Watering Hose: When purchasing a hose, look for one that is double-walled, as it will resist kinking. Quick coupler links are nice to have on ends of hoses to make altering length fast. To extend the life of your hose, keep it wound around a reel and stored in a shady area. Prior to winter freezes, drain hose.

Sprayers: Are commonly thought of as devices for applying chemicals, but can really be a step saver for watering houseplants or small pots of annuals rather that dragging out a hose or making numerous trips with a watering can. The backpack sprayer is best suited for this. Take care not to use any kind of chemical in tanks used for watering!

Sprinklers: Attached to the ends of garden hoses, these act as an economical irrigation system. Standing Spike Sprinklers are usually intended for lawns and deliver water in a circular pattern. Rotating Sprinklers deliver a circle of water and are perfect for lawns, shrubs and flower beds. Pulse-jet sprinklers cover large areas of ground in a pulsating, circular pattern. The head usually sits up on a tall stem, except for when watering lawns. Oscillating sprinklers are best for watering at ground level in a rectangular pattern.

Conditions : Moist and Well Drained

Moist and well drained means exactly what it sounds like. Soil is moist without being soggy because the texture of the soil allows excess moisture to drain away. Most plants like about 1 inch of water per week. Amending your soil with compost will help improve texture and water holding or draining capacity. A 3 inch layer of mulch will help to maintain soil moisture and studies have shown that mulched plants grow faster than non-mulched plants.

Conditions : Normal Watering for Outdoor Plants

Normal watering means that soil should be kept evenly moist and watered regularly, as conditions require. Most plants like 1 inch of water a week during the growing season, but take care not to over water. The first two years after a plant is installed, regular watering is important for establishment. The first year is critical. It is better to water once a week and water deeply, than to water frequently for a few minutes.

Planting

How-to : Planting Perennials

Determine appropriate perennials for your garden by considering sun and shade through the day, exposure, water requirements, climate, soil makeup, seasonal color desired, and position of other garden plants and trees.

The best times to plant are spring and fall, when soil is workable and out of danger of frost. Fall plantings have the advantage that roots can develop and not have to compete with developing top growth as in the spring. Spring is more desirable for perennials that dislike wet conditions or for colder areas, allowing full establishment before first winter. Planting in summer or winter is not advisable for most plants, unless planting a more established sized plant.

To plant container-grown plants: Prepare planting holes with appropriate depth and space between. Water the plant thoroughly and let the excess water drain before carefully removing from the container. Carefully loosen the root ball and place the plant in the hole, working soil around the roots as you fill. If the plant is extremely root bound, separate roots with fingers. A few slits made with a pocket knife are okay, but should be kept to a minimum. Continue filling in soil and water thoroughly, protecting from direct sun until stable.

To plant bare-root plants: Plant as soon as possible after purchase. Prepare suitable planting holes, spread roots and work soil among roots as you fill in. Water well and protect from direct sun until stable.

To plant seedlings: A number of perennials produce self-sown seedlings that can be transplanted. You may also start your own seedling bed for transplanting. Prepare suitable planting holes, spacing appropriately for plant development. Gently lift the seedling and as much surrounding soil as possible with your garden trowel, and replant it immediately, firming soil with fingertips and water well. Shade from direct sun and water regularly until stable.

Problems

Fungi : Rusts

Most rusts are host specific and overwinter on leaves, stems and spent flower debris. Rust often appears as small, bright orange, yellow, or brown pustules on the underside of leaves. If touched, it will leave a colored spot of spores on the finger. Caused by fungi and spread by splashing water or rain, rust is worse when weather is moist.

Prevention and Control: Plant resistant varieties and provide maximum air circulation. Clean up all debris, especially around plants that have had a problem. Do not water from overhead and water only during the day so that plants will have enough time to dry before night. Apply a fungicide labeled for rust on your plant.

Fungi : Powdery Mildew

Powdery Mildew is usually found on plants that do not have enough air circulation or adequate light. Problems are worse where nights are cool and days are warm and humid. The powdery white or gray fungus is usually found on the upper surface of leaves or fruit. Leaves will often turn yellow or brown, curl up, and drop off. New foliage emerges crinkled and distorted. Fruit will be dwarfed and often drops early.

Prevention and Control: Plant resistant varieties and space plants properly so they receive adequate light and air circulation. Always water from below, keeping water off the foliage. This is paramount for roses. Go easy on the nitrogen fertilizer. Apply fungicides according to label directions before problem becomes severe and follow directions exactly, not missing any required treatments. Sanitation is a must - clean up and remove all leaves, flowers, or debris in the fall and destroy.

Pest : Leaf Miners

Leaf Miner is actually a term that applies to various larvae (of moths, beetles, and flies) that tunnel between upper and lower leaf surfaces, leaving a distinctive, squiggly pattern. A female adult can lay several hundred eggs inside the leaf which hatch and give rise to miners. Leaf miners attack ornamentals and vegetables.

Prevention and Control: Keep weeds down and scout individual plants for tell-tale squiggles. Pick and destroy these leaves and take advantage of natural enemies such as parasitic wasps. Know the Growing Degree Days (GDD)* for your area to target insecticide sprays when most beneficial for controlling the specific leaf miner. Seek a professional recommendation and follow all label procedures to a tee. *GDD numbers should be available from your local Cooperative Extension office.

Diseases : Southern Blight

Plants with Southern blight have lesions on the stem at, or near, the soil line. These lesions develop rapidly, girdling the stem and resulting in a sudden and permanent wilting of the plant. High temperatures (above 85 degrees F, 29 degrees C) favor the disease. The fungus attacks a wide range of plants and survives for long periods in soil. To control, treat with a recommended fungicide according to label directions.

Miscellaneous

Glossary : Bird Attracting

The term bird attracting applies to any plant that has flowers, fruit, nuts, or structure that attracts birds. Most plants on ""bird attracting"" lists have favorable fruits or flowers that serve as food, but the trunks, limbs and foliage cover that trees and shrubs provide should not be overlooked as they add shelter for raising young and protection from foul weather.

Glossary : Butterfly Attracting

Many plants, perennials being the largest group, attract butterflies. When you add butterfly attracting plants to your garden, not only do you get to enjoy these winged wonders, but you provide habitats for their survival, as well. Yellows and reds seem to be favorite flower colors, while some plants offer food and shelter for laying eggs on. To complete your habitat, don't forget to add a shallow dish of water.

Conditions : Fall Color

Fall color is the result of trees or shrubs changing colors according to complex chemical formulas present in their leaves. Depending on how much iron, magnesium, phosphorus, or sodium is in the plant, and the acidity of the chemicals in the leaves, leaves might turn amber, gold, red, orange or just fade from green to brown. Scarlet oaks, red maples and sumacs, for instance, have a slightly acidic sap, which causes the leaves to turn bright red. The leaves of some varieties of ash, growing in areas where limestone is present, will turn a regal purplish-blue.

Although many people believe that cooler temperatures are responsible for the color change, the weather has nothing to do with it at all. As the days grow shorter and the nights longer, a chemical clock inside the trees starts up, releasing a hormone which restricts the flow of sap to each leaf. As fall progresses, the sap flow slows and chlorophyll, the chemical that gives the leaves their green color in the spring and summer, disappears. The residual sap becomes more concentrated as it dries, creating the colors of fall.

Glossary : Sandy Loam

Sandy Loam refers to a soil that drains well, with excellent air space, and evenly crumbled texture when squeezed in the hand. A good workable garden soil that benefits from added fertilizer and proper watering. Dark gray to gray-brown in color.

Glossary : Evergreen

Evergreen refers to plants that hold onto their leaves or needles for more than one growing season, shedding them over time. Some plants such as live oaks are evergreen, but commonly shed the majority of their older leaves around the end of January.

Glossary : Perennial

Perennial: traditionally a non-woody plant that lives for two or more growing seasons.

Glossary : Seed Start

Seed Start: easily propagated from seed.

Glossary : Shrub

Shrub: is a deciduous or evergreen woody perennial that has multiple branches that form near its base.

Glossary : Old Fashioned or Heritage Plant

Old Fashioned or Heritage Plant is any plant that is reminiscent of early times or tied to a particular region. Often found in the yards of grandmothers or abandoned home sites.

Glossary : pH

pH, means the potential of Hydrogen, is the measure of alkalinity or acidity. In horticulture, pH refers to the pH of soil. The scale measures from 0, most acid, to 14, most alkaline. Seven is neutral. Most plants prefer a range between 5.5 and about 6.7, an acid range, but there are plenty of other plants that like soil more alkaline, or above 7. A pH of 7 is where the plant can most easily absorb the most nutrients in the soil. Some plants prefer more or less of certain nutrients, and therefore do better at a certain pH.

Glossary : Plant Characteristics

Plant characteristics define the plant, enabling a search that finds specific types of plants such as bulbs, trees, shrubs, grass, perennials, etc.

Glossary : Small Shrub

A small shrub is less than 3 feet tall.

Glossary : Flower Characteristics

Flower characteristics can vary greatly and may help you decide on a ""look or feel"" for your garden. If you're looking for fragrance or large, showy flowers, click these boxes and possibilities that fit your cultural conditions will be shown. If you have no preference, leave boxes unchecked to return a greater number of possibilities.

Glossary : Foliage Characteristics

By searching foliage characteristics, you will have the opportunity to look for foliage with distinguishable features such as variegated leaves, aromatic foliage, or unusual texture, color or shape. This field will be most helpful to you if you are looking for accent plants. If you have no preference, leave this field blank to return a larger selection of plants.

Glossary : Landscape Uses

By searching Landscape Uses, you will be able to pinpoint plants that are best suited for particular uses such as trellises, border plantings, or foundations.

Glossary : Fertilize

Fertilize just before new growth begins with a complete fertilizer.

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