Hardy. A relative term, used to denote a plant which endures the climate (particularly the winter climate) of a given place. Half-hardy plants are those which withstand some frost or uncongenial conditions, but will not endure the severity of the climate. Tender plants are those which are injured by light frosts.
Hedges. Hedges are much less used in this country than in Europe, and for several reasons. Our climate is dry, and most Hedges do not thrive so well here as there; labor is high-priced, and the trimming is therefore likely to be neglected; our farms are so large that much fencing is required; timber and wire are cheaper than live Hedges. However, they are used with good effects about the home grounds. In order to secure a good Hedge, it is necessary to have a thoroughly well-prepared, deep soil, to set the plants close, and to shear them at least twice every year. For evergreen Hedges the most serviceable plant in general is the arborvitæ. The plants may be set at distances of 1 to 2½ feet apart. For choice Hedges about the grounds, particularly outside the northern states, some of the retinosporas are very useful. One of the most satisfactory of all coniferous plants for Hedges is the common hemlock, which stands shearing well and makes a very soft and pleasing mass. The plants may be set from 1 to 3 feet apart. Other plants which hold their leaves and are good for Hedges are the common box and the privets. Box Hedges are the best for very low borders about walks and flower beds. The dwarf variety can be kept down to a height of 6 inches to a foot for any number of years. The larger-growing varieties make excellent Hedges 3, 4 and 5 feet high. The ordinary privet or prim holds its leaves well into winter in the North. The so-called Californian privet holds its leaves rather longer and stands better along the seashore. In the southern states, nothing is better than Citrus trifoliata.
For Hedges of deciduous plants, the most common species are the buckthorn, the European thorn apple or cratægus, osage orange, and various kinds of roses.
Hedges should be trimmed the year after they are set, although they should not be trimmed very closely until they reach the desired or permanent height. Thereafter they should be sheared into the desired form in spring or fall. If the plants are allowed to grow for a year or two without trimming, they lose their lower leaves and become open and straggly. Osage orange and some other plants are plashed—that is, the plants are set at an angle rather than perpendicularly, and they are wired together in such a way that they make an impenetrable barrier just above the surface of the ground.
Helianthus. [See Sunflower.]
Helichrysum. These are perhaps the most popular of the Everlastings ([which see]), having large flowers of several colors. They grow readily from seed, blooming from July to October. Height 10 inches to 2 feet. Should be planted or thinned to stand 18 inches apart.
Heliotrope. A universal favorite house or border plant, growing readily from cuttings or seeds, and producing quantities of fragrant violet, purple or white flowers. One of the best methods of cultivation is to set a strong plant in the border and peg the new growths to the ground, where they will root and form a perfect mat, flowering profusely during the fall months until frost. They will endure the temperature of a living room well if the room is not too dry. Red spider is a natural enemy of the Heliotrope, and when once it obtains a foothold is a very difficult pest to manage, but frequent syringing with water will keep it in check. A light, rich soil and an abundance of heat are their requirements. Height 1 to 3 feet. Propagated by cuttings or layers.
Hellebore (White Hellebore) is often used for the killing of currant-worms and other insects ([see Currant]). It is not so poisonous as the arsenites, and therefore is to be preferred when it is necessary to apply a poison to nearly ripe fruit. It is usually applied in a spray with water, at the rate of ⅓ ounce to the gallon. It is harmless to foliage.
Helleborus, or Christmas Rose, may be had in flower at the holidays if grown in a frame and protected. The usual time for it to flower in the open border is in March or early April. It will continue to bloom for many years if grown in a shady place. Roots may be divided as an increase is wanted. It may also be grown from seeds; and seedlings may be expected to bloom a year from the spring in which they are sown. Height 6 to 10 inches.
Hemerocallis, or Yellow Day Lily. [The advice given under Funkia will apply to this.]