Thrift.—­See “Armeria.”

Thumbergia.—­These slender, rapid-growing climbers are extremely pretty when in bloom during June, but they are only half-hardy; they therefore need greenhouse care, or to be planted in a warm situation.  They flourish best in a mixture of sandy loam and leaf-mould, and may be grown from seed sown in heat (65 to 75 degrees) early in spring.  Cuttings strike readily.  Height, 4 ft.

Thuya (Arbor Vitae).—­Very decorative conifers, mostly of conical shape, and indispensable to the shrubbery.  They thrive in any soil, but prefer a moist situation.  For sheltered positions, where a small dome-shaped bush is required, the Chinese Arbor Vitae (Biota Orientalis) is most desirable; it delights in a heavy soil.  The Biota Elegantissima is one of the most unique hardy shrubs cultivated, and presents a bright golden appearance.  Another effective yellow variety is the Semperaurescens, which retains its colour throughout the winter, and makes a fine pot-plant.  One of the most beautiful of all evergreens is the Thuyopsis Dolabrata; its flat, spray-like leaves are bright green above and silvery below.  The China varieties are somewhat tender, and require protection from frost.  They may all be propagated from seed or by cuttings.

Thymus.—­Effective little perennials for rock-work, growing best in a light, dry, sandy soil.  The hardy kinds like an exposed position; rarer kinds should be grown in pots, as they need protection in winter.  They are easily increased by seed sown in spring, by cuttings or division.  Height, 3 in. to 6 in.

Tiarella.—­These hardy herbaceous plants are very suitable for rock-work or the front of a border.  They are not particular as to soil; they flower in April, and may be propagated by seed or division.  Height, 9 in. to 1 ft.

Tiarella Cordifolia (Foam Flower).—­A hardy herbaceous perennial, having fine foliage.  It will grow in any good soil, but likes shade and moisture.  It may be increased by dividing the roots at the end of the summer.  The blooms are produced during May and June.  Height, 1 ft.

Tigridia (Ferraria; Mexican Tiger Flower, popularly called the Tiger Iris).—­A gorgeous flower of exceptional beauty.  Plant the bulbs in the sunniest spot out of doors during March, April, or May, in a sandy loam enriched with a liberal amount of leaf-mould, placing them 3 in. deep and 6 in. apart, and putting a little silver sand round each bulb before covering it with the soil.  Shelter from cutting winds.  The blossoms appear in July or August.  Each bloom lasts only one day, but is succeeded on the next by fresh ones, so that a continuance of bloom is maintained.  Protect them in winter with a covering of dead leaves, or, better still, take them up when they have done flowering, and keep them dry and free from frost.  For pot-culture plant the bulbs in sandy loam and peat, plunge them in a cold frame, and withhold water until the foliage appears.  They may be increased by off-sets or seeds.  Height, 1 ft.