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Shrub Culture

Potting

Most shrubs require the same potting methods as for canes. Most benefit from being potted lower in the new pot, like canes, to promote new basal growth. Some shrubs are much more sensitive to over watering or soggy soil than canes so the more sensitive types may do better in clay pots. Any shrubs you have tried and not been successful with may do better on a second try using a clay or wooden pot instead. Some shrubs also grow very tall and wide so may benefit from the extra weight of clay pots to keep them from falling over easily.

Pruning

Pruning for shrubs differs somewhat from the methods used for canes. Some that are ever blooming like B.’Concord’ or B.’Ginny’ may need severe pruning to keep them full and compact. Since most ever blooming shrubs don’t branch from nodes where they bloomed, they don’t branch well without help. Hard pruning will force up fresh growth from the roots.

Many shrubs, especially most of the hairy leaved types, have the odd tendency for pruned stems to die back to the soil level. They don’t always come back well from normal or hard pruning. Besides, many are spring blooming so a hard pruning in spring may keep them from blooming that year. The best method for these types and any sensitive shrubs is to wait till they have started putting up new growth from the roots before pruning all old growth down to the soil level. Since most pruned stems will die back to the soil anyway, you might as well cut them back to the soil in the first place. Many such as B. venosa branch ugly anyway so any stems pruned should be pruned down to the soil. Pruning out all of the old growth after the new starts coming up will be less stressful on the plant. Also, getting rid of the old will force even more new growth which will quickly fill the plant back in.

Watering and Fertilizing

Shrubs should be allowed to get slightly dry before watering. Don’t keep constantly wet. Unlike canes, which don’t do much during the winter, many shrubs put out, a burst of growth during winter or early spring. For this reason, they may benefit from being fertilised during a time of the year when you may not be fertilising other types. The easiest rule of thumb to follow is to continue to feed them any time of the year they are actively growing. Quarter strength fertiliser weekly is the best method. Less fertiliser more often is better used than a large amount periodically. Any shrubs that wilt should be examined before automatically giving water. Both over watering and under watering can cause a shrub to wilt. Also, root damage from pests can do the same. If the mix is wet and the plant is wilted, then the lack of water isn’t the problem. Increasing the humidity or removing some of the foliage may be required to help the plant recover from the root damage.

Light and Heat

Most shrubs are very sturdy and some will even grow in full sun in some areas. B.’Concord’, B.’Richmondensis’ and similar types grow quite well in full sun in coastal areas of California. Poor leaf colour or lack of blooms is usually a good sign that the plant isn’t receiving enough light. Undersized or burned leaves is a pretty good sign the plant is receiving too much light. There are shrubs for nearly every light condition except for the deepest shade. Many will even look nice in deep shade, although you will sacrifice blooms in those locations. Many shrubs have such attractive foliage that blooms aren’t necessary anyway so many of them can be used as foliage plants in lower light areas. Nearly all shrubs will perform nicely under early morning sun or filtered sun all day.

Most shrubs are very tolerant of either heat or cold except for the few that require greenhouse care and a few of the distinctive foliage types. Many shrubs continue to grow quite well even through the cooler seasons of the year. Also, unlike canes, they aren’t very prone to leaf drop so their foliage stays attractive all year.

Pests and Diseases

The most common pest that plagues shrubs is mealybugs. Various pesticides will kill this pest. Thrips are sometimes a problem and this damage show up as distorted new leaves or leaves with brown damaged areas on leaf veins or other parts of the leaf. Thrips may require a stronger pesticide and several treatments to get rid of. Thrips are hard to find so are mostly suspected by the particular damage to the plant. You should suspect this pest any time a shrub starts putting out damaged leaves or flowers.

As a group, shrub type begonias are generally disease free. A few distinctive foliage types are prone to mildew during cold weather which can be controlled with a fungicide. You can also try moving prone plants to a different location to find one it likes better. Some of the hairy leaved types are prone to either mildew or damaged leaves if they are in an area where the leaves get wet constantly. Many hairy ones such as B.’John Tapia’ don’t do well in areas where they are watered with sprayers that get the leaves wet. Getting leaves wet under ordinary watering conditions doesn’t seem to be a problem especially if they’re in an area where there is enough circulation to dry them off quickly.

Propagation

As a general rule, most shrubs will only start from stem cuttings. There are a handful that will start from leaves however. Consult an experienced grower for specific plants that may start from leaf cuttings. The most likely candidates for growing from leaves are B. luxurians and any shrubs of mixed parentage such as a shrub/rhizomatous hybrid. If one parent will start from a leaf, the progeny may also.

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As a general rule, though, stem cuttings are best. Some will start in water, mainly the bare leaved types. Most, especially the hairy leaved types, do best started in mix or perlite. Many will root without extra humidity such as provided by a sweater box, but all will root faster using an enclosed container for rooting.

Special Uses and Tips

There are shrubs for nearly every type of usage. Some make excellent bedding plants. Many will grow on trellises, some can even be trained as standards. A good share will make large specimen plants when planted in the ground or moved up gradually to large pots. There are dozens of shrubs that can be made into excellent hanging baskets.

Credits / references:
Brad Thompson | Brad’s Begonia World