Nolana.--Hardy annuals that are suitable for the border, as they are
very showy when in flower. The seed should be sown in spring on a
gentle hotbed, and the plants transferred to the garden about the
middle of May. N. Atriplicifolia may be sown in the open in the
autumn. They flower in July and August. Height, 6 in. to 2 ft.
North Borders, Plants suitable for.--Hardy Camellias, Chrysanthemums,
black and green Tea Plant, Rhododendrons, Ferns, Red Currants, Morello
Cherries, and spring and summer cuttings of all sorts.
Nuttallia.--This early-flowering shrub is only hardy in the south and
south-west of our country. It requires a light, rich soil, and may be
increased by division. Racemes of white flowers are produced during
February and March. Height, 2 ft.
Nycterina.--Exquisite little half-hardy plants, suitable for pots or
rock-work. The seed should be sown early in spring on a gentle hotbed,
and the young plants transferred to the pots or open ground at the end
of May, using a light, rich soil. Height, 3 in.
Nymphaea Alba.--A hardy aquatic perennial, frequently found in our
ponds. It flowers in June, and may be increased by dividing the roots.
Height, 1 ft.
O
Odontoglossum Grande.--A most beautiful orchid, delighting in a
temperature of from 60 to 70 degrees and an abundance of water during
summer, but good drainage is essential. The blooms are yellow, spotted
and streaked with venetian red, and are often 6 in. across. The pots
should be two-thirds filled with crocks, then filled up with fibrous
peat and sphagnum moss. During winter only a very little moisture
should be given.
Oenothera.--The Evening Primroses are most useful and beautiful
plants, well suited for ornamenting borders, beds, edgings, or
rock-work. All the species are free-flowering, and grow well in any
good, rich soil. The annual and biennial kinds are sown in the open
in spring. The perennials may be increased by dividing the roots, by
cuttings, or by seed, the plants from which will flower the first
season if sown early in spring. They bloom in June and July. Height, 6
in. to 4 ft.
Olearia.--These evergreen shrubs thrive in peat and loam, and may be
increased by division of the roots. O. Haastii has foliage resembling
the Box, and a profusion of white, sweet-scented flowers in summer: a
chalk soil suits it admirably. Height, 3 ft. to 4 ft.
Omphalodes Verna.--A hardy perennial which may be grown under the
shade of trees in ordinary soil. It produces its flowers in March, and
is increased by dividing the roots in autumn. Height, 6 in.
Oncidium Sarcodes.--Plant these Orchids firmly in well-drained pots,
using equal parts of live sphagnum and fibrous peat. Give one good
watering as soon as the potting is finished, and stand them in a
light, warm part of the greenhouse. They will require very little more
water until the roots have taken hold of the soil--only sufficient to
keep the pseudo-bulbs from shrivelling--and during the winter months
scarcely any moisture is needed. They flower in August. Height, 1-1/2
ft.
Onions.--Require a deep, rich, heavy soil. Where the ground is not
suitable it should have had a good dressing of rotten manure the
previous autumn, and left in ridges during the winter. Level the
ground, and make it very firm just before the time of sowing. The seed
should be sown early in March for the main crop and for salad and
pickling Onions, and in August for summer use. Thin out to about 6
in. apart, excepting those intended to be gathered while small. The
Tripoli varieties attain a large size if transplanted in the spring.
The Silver-skins do best on a poor soil. For exhibition Onions sow in
boxes early in February in a greenhouse; when about 1 in. high prick
out, 3 in. apart, into other boxes; give gentle heat and plenty of
air, and when they have grown 6 in. high put them in a cool frame
until the middle of April, when they must be planted in the open, 1
ft. apart.
Ononis Rotundifolia (_Round-leaved Restharrow_).--A charming hardy
evergreen of a shrubby nature. It will grow in any ordinary garden
soil, and is increased by seed, sown as soon as it is ripe. It is most
effective in clumps, and blooms from June to September. Height, 1-1/2
ft.
Onopordon.--Half-hardy perennials of a rather interesting nature and
of easy cultivation. Sow the seed any time between March and June.
They require the protection of a frame or greenhouse during winter,
and produce flowers in July. Height, 6 in. to 8 ft.
Onosma Taurica (_Golden Drop_).--This hardy herbaceous plant is very
pretty when in flower, and suitable for rock-work. It requires a
well-drained vegetable mould, and to be planted where it can obtain
plenty of sun. It is increased from cuttings taken in summer, placed
in a cucumber frame, kept shaded for about a fortnight, and hardened
off before the winter. The flowers succeed one another from June to
November. Height, 1 ft.
Opuntia Rafinesquii (_Hardy Prickly Fig_).--A dwarf hardy Cactus with
sulphur-coloured flowers, produced from June to August; very suitable
for dry spots in rock-work. It grows best in peat with a little sand,
and is propagated by separating the branches at a joint, and allowing
them to dry for a day or so before putting them into the soil. Height,
2 ft.