Topic 5

One of the most critical determinants of a green roof’s performance is the type of vegetation planted on its surface. For a diversity in color, shape, and texture a mix of annuals, perennials, small trees, and shrubs should considered to select for the installation of a green roof.

Shrubs are worth mentioning because they provide privacy and protection against wind damage. Hardy, drought-tolerant plants that can thrive in sunny, windy, and hot or cold conditions will grow better.

A few other examples of plants to try out in urban environment are lavenders, pelargoniums, salvias, impatiens, verbenas, fuchsias, rudbeckias, petunias, achilleas, echinaceas, catmints, tulips, hyacinths, daffodils, herbs, succulents, vegetables and fruits, ornamental grasses, dwarf boxwood shrubs and evergreen trees.

Further on, the main features of each one will be listed.

Sedums (Sedum) are one of the star plants for creating a green roof, and a sedum roof needs no extra growing medium. As well as affording excellent ground cover, this hardy, easy-to-maintain plant grows happily in a shallow layer of substrate, minimizing the amount of pressure it puts on a structure.

Houseleek is in fact a plant of two genus – Sempervivum and Jovibarba. These evergreen, alpine plants are incredibly hardy and can even survive growing in bricks or rocks. Ideal for a green roof, houseleeks are eye catching, with their mass of rosettes and spiral foliage bearing attractive flowers in summer. There are many varieties of houseleek, with the cobweb species being one of the most popular.

There are many cultivated varieties of Lavandula angustifolia. These plants usually are growing in flower beds in cool climate zones (zone 5 or 6). Can be damaged by frost in containers. Other lavender species can be grown like annuals.

Pelargoniums (Pelargonium) are easy to grow and are often etched into the memory of those who grew them as children simply from cuttings. Pelargoniums are varied in their appearance and are available in a wide variety of species and cultivars that can be utilized in the garden in various ways.

Salvias, also called sages, are easy to grow, bloom abundantly, and look great in the landscape. The Salvia genus is huge. There are over 700 different species. Salvia splendens, Salvia patens, Salvia farinacea, Salvia coccinea are growing like annuals. Salvia nemorosa, Salvia officinalis and Salvia pratensis are perennial plants. Blooms of most salvia plants are long-lasting and attract butterflies and pollinators, which are always good for the garden.

Impatiens (Impatiens) plants are normally purchased as well-rooted plants from the garden center. They can also be propagated from seeds or cuttings very easily. They are very sensitive to lack of water and will wilt quickly if they lack water. They enjoy moist but well-draining soil and partial to deep shade.

While the verbena flower is drought resistant, the blooms are improved with regular watering. Verbena hybrida is growing in containers mostly. Colorful and scented verbena flowers provide a rich source of nectar for pollinators, attracting bees and many types of butterflies.

The Fuschia genus contains more than 100 woody shrubs and trees, but the familiar garden fuschias widely available in garden centers are mostly hybrids chosen because they are ideal for hanging baskets and other containers. Most will thrive in part shade to full shade. They don’t like to be too hot, and they especially hate dry heat.

The starry flowers of these robust, long-flowering plants can shine in borders and containers and prairie-style plantings. Perennials tend to be yellow flowered, whereas those grown as annuals are available in a wider colour range, with shades of yellow, orange, dark red or brown. The foliage can be hairy or smooth and comes in green or grey. Rudbeckia have daisy-like flowers that provide a blaze of colour in late summer. They are generally low maintenance, have a long flowering season and are good for wildlife.

Care of petunias will include regular fertilization with a balanced, water soluble fertilizer designed for blooming plants. As they are heavy feeders, petunias care will also include weekly feedings. Proper light, water, and fertilization when caring for petunias will ensure a long season of beautiful blooms.

Houseleek is in fact a plant of two genus – Sempervivum and Jovibarba. These evergreen, alpine plants are incredibly hardy and can even survive growing in bricks or rocks. Ideal for a green roof, houseleeks are eye catching, with their mass of rosettes and spiral foliage bearing attractive flowers in summer. There are many varieties of houseleek, with the cobweb species being one of the most popular.

Achillea are totally hardy and totally reliable flowering herbaceous plants for any garden. They are perennials from the northern hemisphere from grassland areas but have been bred, varied in colour and improved for garden use by generations of breeding work. Achillea have aromatic leaves which are grey or green with pinnate fern-like leaves and daisy like flower heads in corymbs both in summer and on into autumn. As such they are ideal plants for any planting and grow well alongside a whole host of other summer and autumn flowering herbaceous plants.

With its season-long colorful display of daisy-like flowers, Echinacea is the perfect perennial for sunny locations. The striking, colorful, and fragrant flowers have a prominent central cone held high on sturdy stems. Recent breeding efforts have resulted in an ever expanding range of flower colors, blooming characteristics, and plant habits. They produce masses of eye-catching blossoms in the mid-summer that last through the remainder of the growing season. Today’s cultivars produce a wide range of flower colorations consisting of various hues of magenta, orange, pink, purple, white, and yellow.

Catmint (Nepeta) is a perennial herb that is a member of the mint family. It is an extremely easy-growing plant with few pests or problems. Nepeta has slightly aromatic gray-green foliage with a delicate, lacy appearance. Its billowing foliage is topped with spikes of flowers in early summer, with repeat blooms throughout the season. The flowers can be white, pink, or lavender-blue.

In pots, tulips (Tulipa), hyacints (Hyacinthus) and daffodils (Narcissus) are eye-catching, portable, and protected. The best time to pot up bulbs is in early fall, the same as if they were planted in the ground. Have ready several containers with outside diameters of at least 45 cm and outside heights of at least 40 cm. Using anything smaller reduces the impact of the planting and the viability of the bulbs.

Almost any herb can be grown in a container. However, if herbs are mixed in the same pot, it should  be assured that plants have similar growing requirements. For example, some herb plants need more water than others, and some are finicky about how much light they get.

Most popular herbs:

  • basil (Ocimum basilicum),
  • chives (Allium schoenoprasum),
  • coriander (Coriandrum sativum),
  • tarragon (Artemisia dracunculus),
  • lemon balm (Melissa oficinalis),
  • marjoram (Origanum majorana),
  • oregano (Origanum vulgare),
  • mint (Menta ×piperita, Mentha spicata),
  • rosemary (Rosmarinus officinalis),
  • lavender (Lavandula angustifolia),
  • thyme (Thymus vulgaris).

For some gardeners, growing vegetables in containers is a necessity. Urban gardening often means growing on rooftops, balconies or whatever little space the gardener has available.

As a general rule, select as large a container as possible. Small containers dry out more quickly and may need daily watering. Self-watering planters designed for urban balconies and patios extend the time between watering.

The Best Vegetables for Containers:

Lettuce, radishes, other salad greens, bush beans, garlic, kohlrabi, onions, Asian greens, peas, pole beans, carrots, chard, cucumber, eggplant, fennel, leeks, peppers, spinach, parsley, beets, broccoli, okra, potatoes, sweet corn, summer squash, dill, lemongrass.

Certain combinations of plants make them more productive—often because some plants have complementary characteristics, such as their nutrient requirements, growth habits, or pest-repelling abilities.

Good companion plants:

•    beans, carrots, squash,

•    eggplant, beans,

•    tomatoes, basil, onions,

•    lettuce, herbs,

•    spinach, chard, onions.

Combinations to avoid:

•    beans with onions and garlic,

•    carrots with dill or fennel,

•    tomatoes or squash with potatoes,

•    onions with beans and peas.

The best fruit trees for containers are fruit trees that have been grafted onto dwarf rootstock. Many types of soft fruits can also be grown (fruits that don’t grow on trees) in pots. So long as adequate sun is available, the container can be placed on a patio, deck, balcony or anywhere where there is space.

It should be checked how fruit tree pollinates to be sure it can flower and then fruit. Self-fertile plants generally do not require another plant for pollination although it is often recommended as insurance. Self-sterile plants like blueberries require a different blueberry variety nearby to ensure pollination. All of them should be available to pollinators like bees, other insects, and wind to assist moving pollen from one flower to another.

Ornamental grasses are an excellent way to create privacy in the garden, especially on a patio, balcony or rooftop. Some of the grasses are extremely resistant to drought and grow rapidly.

Best ornamental grases:

  • fountain grass (Pennisetum setaceum),
  • blue lyme grass (Leymus arenarius),
  • New Zealand flax (Phormium tenax),
  • miscanthus (Miscanthus sinensis),
  • blue oat grass (Helictotrichon sempervirens),
  • Mexican feather grass (Stipa tenuissima).

Most of the garden forms are cultivars or hybrids of two species— Buxus sempervirens (common box) and Buxus microphylla (Japanese box). Boxwoods are typically large shrubs or small trees, but most of the varieties used in modern landscaping are dwarf varieties.

These dwarf boxwood shrubs are prized for their densely packed, light-green leaves and rounded, compact growth habit.

Evergreen conifers, such as pine, juniper, and fir, make good container plants, offering year-round interest and structure on patios, terraces and balconies. All conifer require well-draining soil in a container, and most thrive in a spot with full sun.