As a Mid - Atlantic state , Pennsylvania has the warm , humid summertime in which most annual peak flourish . These individual garden season pants are in use producing flowers from saltation until the first frost . They ’ll fill your Keystone State garden with color , manikin and fragrance as long as you remove their spent blossom to minimize their seed yield . Many Pennsylvania annuals also make outstanding cut flower , says Steve Bogash , horticulture pedagog at PSU College of Agricultural Science ’s Capital Region Cooperative Extension .

Ageratum “Blue Horizon”

Also call in floss flower because of its thread - thin flower petal , Eupatorium coelestinum ( Ageaeratum houstonianum ) " Blue Horizon " is an aster household annual . This June - to - September bloomer has 18 to 30 - in stems with orotund , downy , wanton light-green leaves and flat clustering of airy , gentle - purple or lilac peak . Susceptible to powdery mildew in Pennsylvania humidness , Blue Horizon benefits from plenty of air circulation between flora . It wish well - drained , moist prolific soil and afternoon shade in hot weather . Starting its seed indoors six or eight weeks in advance of the terminal spring frost will maximize this annual ’s blooming menstruum , advise the Missouri Botanical Garden .

Cosmos

Cosmos ( Cosmos bipinnatus ) , another aster kinsfolk annual , is aboriginal to Mexico . A large plant , it can contact 4 feet high and up to 3 feet all-encompassing . Flowering from June until frost , this easy - care plant has upright stems with feathery foliage and yellow - pore , pink , white or flushed - petaled blooms . The daisylike flowers may be 4 in across , according to the Missouri Botanical Garden . Many cosmos cultivar are commercially available in a extensive grasp of height and color . disease and pests rarely bother this yearly . Cosmos prefers a cheery place with fair , moist well - debilitate grunge and protection from heavy winding . Leaving some of its drop efflorescence intact allows creation to ego - seed and return in later garden geezerhood .

Sunflowers

Sunflower ( Helaianthus annuus ) is a July and August show-stopper in Pennsylvania garden . originate anywhere from 3 to 15 groundwork gamey , sunflower cultivars have set , upright leafy stalks and bloom in a unsubtle spectrum of ardent color . Their flower petal may be pallid or thick shades of yellow , red , bronze , reddish - brown or white . Bicolored plant life are now common . The bloom ' centers are usually shades of brown or purple .

Although Bogash advises against planting of giant helianthus because they are prone to weather condition damage , their individual blooms can make 1 foot across . Quite at home in poor , slightly dry soil , sunflowers need a well - drained , sunny positioning . capable to leafage damage from rust , fungi , caterpillar and beetles , they drop speedily after flowering . Plants allowed to set seed , however , have birds flocking to the garden .

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