Seasonal plants will need more feeding than a permanent planting display, since things like annuals, tender perennials and bulbs grow fast and quickly exhaust the soil. Peat-based composts used for seasonal plants also tend to lose their plant foods quickly, these being easily washed out by rain and watering. Peat composts will feed the plants adequately for a few weeks after first being planted, but after that, you should water with liquid fertilizer every two or three weeks during summer. Feed winter and spring seasonal plants including bulbs) less frequently, say once immediately after planting and once or twice in the spring.
The best liquid fertilizers to use are those with a high-potash content, which encourages flowering rather than excessive foliage growth (tomato fertilizer is suitable, being very high in potash). Liquid feeds which also contain trace elements are particularly good, preventing deficiencies of these essential minerals.
Permanent plantings require less heavy feeding. For one thing, the soil-based composts in which they’re usually grown hold plant nutrients longer; secondly you don’t want the plants to grow too vigorously or they may quickly become too large for the box; and thirdly, most of the smaller flowering perennials generally bloom more freely when not over-fed. One dose of a high-potash liquid fertilizer in the spring should do (with a second dose in summer only if the plants look like they really need a boost).
If the growing compost is dry, give your plants some water before feeding with liquid fertilizer; applied to dry compost, it may harm the roots, and never make the mixture stronger than recommended on the bottle.
HANGING BASKETS
Wire baskets should be lined with moss (available from garden stores) and filled with a peat-based potting compost. One or two trailing plants may be inserted in the sides, to grow out through the wire and moss. Place these in position as you line and fill the basket. Finally, plant the top with more trailers and some taller and bushier things. Bring the moss right to the brim of the basket, but the compost level should be below this, to allow for watering. After planting, give the basket a good soaking and keep it out of the sun for a couple of days, if possible, to let the plants settle in before hanging.
Baskets do dry out fast and may need watering once or even twice a day in hot weather. The most effective way to water is to take the basket down and dunk it in a bowl of water until the compost is soaked through. In very hot weather, it’s best to do this at least once or twice a week, in addition to a daily sprinkling with the watering can. Feed with liquid fertilizer every two or three weeks.
If you’re unable to carry out such frequent watering in summer, put a lining of polythene inside the moss to help conserve the moisture. But be sure to punch some holes in the base of the polythene to allow for drainage of excess water; and make slits in the sides to allow you to plant trailers. Placing a saucer on the moss lining in the base, before filling with compost, also helps to prevent water from draining away too quickly, and to hold a small reserve of moisture for the roots.
Solid plastic hanging plant containers require less frequent watering (although they’ll still dry out quite fast) but then you can’t plant trailers in the sides of these; and I do like the attractive moss-lined effect of the traditional open basket.
GENERAL CARE
One of the most important periodic tasks is to nip off dead flower heads, to prevent energy being wasted on seed production and to encourage prolonged flowering instead.
Often, trimming a plant with shears or scissors after it finishes flowering will induce it to produce a second flush of colour. This is worth trying with all plants that make strong, straggly growth, although not all will respond. Trimming is to be recommended in any case for the strongest-growing perennials like aubrietas, arabis, Alyssum saxatile, campanulas, helianthemums and Iberis sempervirens (candytuft). Cutting back the spent flowering shoots keeps them neat as well as ensuring good flowering the following year, and quite possibly some extra flowers the same year. Try this with annuals, too.
Weeding is the only other regular task. In the crowded conditions of a window box or hanging basket, added competition for root space, water and food is the last thing your plants need, so get any weeds out as soon as you spot them, and before they become large enough to provide serious root competition.
