Although many people plant crabapples, most cultivars are not really suitable for a small garden. They grow too large, have low profiles-making mowing under them difficult-and many commonly available types are susceptible to diseases such as fire blight and apple scab. The sargent crabapple (Malus sargentii, Zone 5) is different. It's a tiny tree that grows less than two metres tall and three metres wide, has good disease resistance and thrives in most soils. In spring, red buds open into white flowers, which give rise to small, bright red fruit. 'Tina' is said to be an even smaller cultivar and is worth searching for.
Another suitable crabapple is the upright Siberian crab (M. baccata 'Columnaris', Zone 2). Opposite to those of the 'Walker' peashrub, its branches turn upward to form a narrow column that will reach about nine metres tall by only 1.5 metres wide. It prefers a medium soil and at least half a day of sun. The white flowers are followed by small red or yellow fruits that birds enjoy, so there is no cleanup problem from fallen fruit.
One of the most striking spring-flowering trees is the golden chain (Laburnum x watereri 'Vossii', Zone 6), with its pendulous flower chains, which can be up to 45 centimetres long. Grow this in well-drained soil in full sun and in a spot where the olive green bark can be appreciated from indoors in winter. The tree will reach about 4.5 metres by 3.5 metres. It can be trained over a pergola to make an interesting entrance to a garden. On the downside, the seeds are poisonous, so avoid planting it close to a sidewalk where children might pick them up.
The Double flowering almond (Prunus triloba 'Multiplex', Zone 2b) can be purchased as either a shrub or a tree. The tree form is usually grafted onto a 1.5-metre stem and makes a good small tree that will slowly grow to about five metres tall by three metres wide. The spring flowers are like tiny, pink cotton balls that clothe the branches so thickly they almost hide the leaves. Garden centres may carry it under the name 'Plena'.
If you fancy a tree with coloured foliage, try a chokecherry (P. virginiana, Zone 2) cultivar such as 'Schubert', also known as 'Canada Red'. This tree has a rounded head that will reach about seven metres tall and six metres wide, but it will take 30 years for it to reach that size. The foliage opens green, then darkens to a dull purple, and the white spring flowers give purple fruit that can be used for preserves if you add lots of sugar.
There are many conifers that can be used in a small garden to add height and winter interest. Conical forms include the dwarf Alberta spruce (Picea glauca var. albertiana 'Conica', Zone 4) and several cultivars of white cedar (Thuja occidentalis, Zone 3), including bright green 'Holmstrup' and 'Reingold', with golden foliage that turns coppery in winter. The Alberta spruce will reach three metres, the others only two, in about 30 years.
For a columnar shape, choose between the dwarf Serbian spruce (P. omorika 'Nana', Zone 2b), upright forms of white cedar such as T. o. 'Fastigiata' and 'Unicorn', and numerous narrow forms of juniper, such as Juniperus chinensis 'Fairview' (Zone 5), J. scopulorum 'Skyrocket' (Zone 3) and J. virginiana 'Manhattan Blue' (Zone 2b). Those will all grow three to five metres tall at maturity and are suitable for most soils.