Panicum - Crab Grass Millet! There is a superb bronze leaved form - Panicum miliaceum 'Violaceum'.
Pennisetum - Ornamental Grass A good range of ornamental garden grasses which are perennial. The Squirrel Tail Grass being one of the most popular.
Penstemon - Penstemon Much hardier than was at one time thought. Maybe winters are getting milder! Colours from pure white through to deepest mauve or purple. Semi-evergreen rather than fully evergreen, and gets knocked back in most winters.
Polystichum - Hardy Fern - Some of the most beautiful sights I have seen in the spring, have been members of the Polystichum diversilobum group breaking into growth. They are pretty good for the rest of the year as well!
Pachyphragma - Evergreen or sometimes semi-evergreen member of the cabbage family. White flowers which are not noted as being of nice scent!
Pachysandra -Can be quite a boring plant unless properly planted and grown. Evergreen so hailed as a groundcover, but needs a few years to get settled.
Paeonia - If you want months of flower, look elsewhere, but if you are happy with the magnificent early display these give, look no further. There are some superb colour variations moving away from the deep crimson of the old fashioned Peony. For something different, try one of the tree peonies. But those are officially 'shrubs', but they still blend in well with perennial plantings.
Papaver - Some very spectacular Poppies amongst the perennial types Papaver orientalis being the most popular. Huge flowers - mainly scarlet but sometimes pink, with attractive foliage clump. At the other end of the scale, there are the Alpine poppies that come in many of the pastel shades.
Parahebe - Most of the common ones have blue flowers, but there are also pinks. Evergreen and low growing are an advantage - good for borders various or rock garden.
Paraquilegia - Small, tufted herbaceous perennial suited to the rock garden. ferny foliage and upward facing bowl shaped flowers - not unlike some Anemones.
Paris - Daiswa - i do not know it, I have never seen it as far as I am aware. I will investigate!
Parnassia - The Star of the Bog. White or sometimes pale yellow flowers - not unlike the old fashioned mossy Saxifrage.
Parochetus - The Shamrock Pea. Shamrock on account of its foliage, and Pea on account of its flowers. Low growing herbaceous perennial that will need some winter protection.
Pentaglottis - Similar in many respects to the Borage, and often named as Anchusa.
Persicaria - Generally creeping perennials at different heights, but all in shades of pink or red. Good ground cover though not evergreen.
Petasites - Winter flowering with unusual flowers and leaves. Not particularly showy, but it is a winter flowering addition.
Petrocallis - Typical Alpine perennial that will need to be in traditional well drained rockery area. Cold wet feet in the winter i a killer for this plant. But forms nice evergreen cushion and blue-pink flowers.
Phegopteris - Hardy Fern -The Beech Fern. Bright green 'typical' fern foliage, but deciduous. Prefers good shade cover - and damp.
Phlomis - Interesting flowers, drooping tubular with large 'lips' set in whorls around stems giving a slight candelabra effect. Mainly grey green downy foliage.
Phlox - Upright perennials or low growing alpines. The low-growing alpine types are generally evergreen. Some prefer a good fertile soil, others for thin well drained soil. Many of the low ones are suited to walls and the like.
Phormium - New Zealand Flax - Evergreen perennials though often sold as shrubs. Whichever, they all have interesting lance-like foliage wit a wide range of colours in including stripes.
Phuopsis - Interesting foliage and flowers on this ground hugging evergreen perennial. Spreads well but is not invasive. Pink flowers make up a pompom shaped bloom.
Phygelius - Sub shrubs that act like perennials! Well at home in perennial border settings. Drooping tubular flowers, and heights ranging from 60cm to 1.3m. They are basically evergreen but suffer in severe winters (but shoot out again the following spring.)
Pyrethrum - Confusion exists in the proper classification of the old fashioned garden plants known as Pyrethrums. We will give the their own section for now. ferny foliage and showy daisy flowers in many colours - all with the central yellow area, other than the double flowered types.
Physalis - Chinese Lanterns. Non evergreen, but erect stems bearing the well-known red Chinese Lantern flowers. Left on the plant, they are useful additions to the autumn and winter garden.
Physotegia - The Obedient Plant, so-named because the flowers can be eased from side to side and will stay where you place them! Other than that, they are an attractive addition to perennial bed or container. Mainly pink flower spikes made up from many individual loosely tubular flowers.
Phytolacca - Pokeweed. Shrubby perennial for the back of a border. The near black berry clusters are the main attraction. 1.2m tall.
Platycodon - The Balloon Flower, but with open bells similar to many Campanulas. Low growing and preferring a good moist soil. Quite showy and flowers late summer. Small balloons burst open to loose bells of blues, pinks or white.
Podophyllum - Creeping groundcover perennial with attractive marks on palmate foliage.
Polemonium - Jacob's Ladder - Herbaceous perennial with attractive foliage. Seemingly happiest in dry areas, which is where I have gown and photographed them. The blue Polemonium caeruleum is the true Jacob's Ladder, by P pauciflorum is also good - but different.
Polygala - Snakeroot - Pea flowers - the blues are best - on carpets of leathery foliage. Evergreen so good for medium groundcover. Dappled shade suits, but also full sun.
Polygonatum - Solomon's Seal - Arching stems of pendulous tubular flowers. Good woodland or border plants. Early flowering then foliage dies back.
Polypodium - Hardy Fern - A few golden foliage types in this group. Not deciduous but still worth growing.
Potentilla - Perennial Types - Far better and more dependable than the shrub sections of Potentilla - for me! (Stand by for the flak!).
Pratia - Low growing, even ground-hugging and masses of blue star flowers. Good on the rockery or front of border, and well suited to an alpine trough.
Primula - Not just the primroses, but many other desirable perennials for most garden situations - damp, dry shaded even or bright sun.
Prunella - Self Heal - nearly evergreen in a mild winter. Violet blue flowers in profusion for mid-summer.
Pulmonaria - What a lovely group of plants these are. Good foliage effect, bright colours in spring to early summer, ground cover, sometimes evergreen. White, blue, pink throughout the range and trouble-free until they get mildew - dry hot summers!
Pulsatilla - A beautiful sight in early spring with the Anemone-type flowers held above hairy foliage, and then later as the flowers give way to the seedheads.
Puschkinia -Halfway between dwarf hyacinths and tall
Scillas. Hardier than the Scillas and easier to grow long term than
Hyacinths. White star flowers in clusters with subtle light blue
markings for some.