Autumn Is For Planting – Especially Bulbs

81024thumbAutumn is for planting. Cliche? Yes; but true. Autumn is when most plants are beginning dormancy, and are therefore not so bothered by the discomforts associated with transplant. The weather is cooler and wetter, so that even if they are bothered, such discomforts are not as discomforting as they would be in summer. Once in the ground, plants have a few months to recover before spring.

The two main exceptions to the rule that ‘autumn is for planting’ are plants that are sensitive to frost, and bare root plants. Plants that are sensitive to frost should obviously be planted after the last frost date, at the far end of winter. Bare roots plants do not wait that long, but should wait until they are completely dormant in mid winter before being dug, separated from their soil, and relocated.

Dormant bulbs and bulb like plants, including corms, rhizomes, tubers and tuberous roots, epitomize the autumn planting rule. They must be planted while dormant in autumn or winter. They arrive in nurseries about the same time that they should be planted into the garden. Spring blooming bulbs become available and should be planted earliest. Summer bulbs become available a bit later.

Daffodil, narcissus, tulip, crocus, hyacinth, grape hyacinth, freesia, anemone, ranunculus, montbretia, crocosmia, most lily and some types of iris will all want to get into the ground when the rain starts. Rain leaching through the soil around them, as well as cooler temperatures through winter, tell them what time of year it is, so that they will be ready to bloom when weather warms in spring.

Each type of bulb prefers to be planted at a particular depth. Bearded iris rhizomes want to be buried horizontally, just below the soil surface. As long as the latest get planted within their respective planting season, some types of bulbs can be planted in phases every week or two, so that a later phase starts to bloom as an earlier phase finishes. Daffodil, narcissus and especially grape hyacinth have the potential to naturalize and bloom annually. Montbretia and crocosmia can be downright invasive.

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Division Is Equal To Multiplication

70809thumbMathematically, division is the opposite of multiplication. Horticulturally, they are the same. Digging and splitting overgrown perennials to propagate them is known as ‘division’ because it divides many rooted stems or rhizomes of one plant into many new plants. Division is a form of propagation; and propagation is commonly known as multiplication. So, we divide plants to multiply them.

Autumn is generally the best time for panting. It is after most of the warmest and driest weather, and just before the cool and rainy weather that keeps newly planted plants from getting too dry. It seems obvious that autumn would also be the best time for division. However, a few perennials that are dormant or mostly dormant by the middle of summer can be divided now for an early start.

Bearded iris may not look dormant with their leaves still green, but they are about as dormant now as they will get. If divided now and allowed to slowly disperse roots through the remainder of summer, they can prioritize the production of new foliage when they come out of dormancy in autumn, like they would do naturally. Like many perennials in mild climates, they grow through winter.

Once dug, the plump rhizomes need to be separated from the old shriveled rhizomes that they grew from. For most, the best segments of rhizome are between the leafy tips and the stalks of the flowers that bloomed earlier this year, although it may not be easy to see where floral stalks were attached. The older sections of rhizome behind the flower stems are probably shriveled already.

The freshly divided segments of rhizome should then be groomed of deteriorating old leaves. Remaining green leaves can be cut in half to remove drying tips. Rhizomes then get replanted just below the surface, with the perpendicular fans of foliage standing upright. The main difficulty with dividing iris now is that they will need to be watered until the rain starts late in autumn. Bergenia, lily-of-the-Nile and a variety of perennials with big rhizomes get divided in a similar manner.

Annuals Just Might Be Perennials

70614thumbAnnuals come and annuals go. There are cool season annuals for winter. There are warm season annuals for summer. Really though, there are all sorts of annuals that are not annuals at all. Most are some sort of perennial that has the potential to last longer than a single season. Only a few popular ‘annuals’ would necessarily die after blooming and producing seed, within a single year.

To be clear, true annuals last only a single year. They probably germinate from seed early in spring, and grow quickly. They then bloom in spring or at least by summer, and subsequently produce seed. Once their seed has matured and been dispersed, their job is done. They finally die in late autumn or winter. Annuals from deserts are even faster because of the harshness of the weather.

Many large-flowered sunflowers are true annuals. They are finished once their seeds mature. They will not bloom again. Even if they wanted to, they would not survive through winter. Petunias should be annuals, because they also die over winter. However, it is possible for them to survive winter in a semi-dormant state, and regenerate and bloom again the following spring and summer.

Realistically, it is not practical to salvage petunias for a second year. It is easier and more efficient to plant new ones. Yet, it sometimes happens, particularly in mixed plantings where old plants can get cut back while cool season annuals dominate in winter. Alternatively, lanky old stems can get buried with only their tips exposed. These tips might grow as new plants the following spring.

Cyclamen are cool season annuals that have been dieing back for summer. They usually get removed by now. However, in mixed plantings, some of their fat tubers can survive through summer to regenerate next autumn. For what they cost, they are worth salvaging! Primrose, chrysanthemum, impatiens and the various fibrous begonias are all worth salvaging through their off seasons.

Fibrous begonias may not know what their off season is. Those that bloomed through winter might be looking tired by now. If pruned back, they could regenerate as warm season annuals. Those planted in spring might look tired by the end of summer. If pruned back early enough in autumn, and protected from frost, they might grow enough before winter to work as cool season annuals. Cutting them back and waiting for regeneration may not be much more effort than replacing old plants with new ones, and is less expensive.