Late Spring Jobs in the Flower Garden

Jobs to do

Preparing the soil for sowing seed outdoors

You will need to fork and rake the soil into a good condition for sowing various seeds, mostly in beds and borders, and it should be much easier to do than it was earlier in the spring. A section of the nursery bed will need to be prepared for seeds as well. In all cases, do try to make sure the seed-bed is level and evenly firm, otherwise you will have patchy germination and weak plants. Hollows and bumps mean that seeds are washed by rain into clumps, and soil which has been firmed too thoroughly will be badly drained.

Preparing compost for sowing seed under glass

This in fact may have already been done, if you made up a good quantity in mid-spring. If you are short of time, you can use ready-made John Innes Seed Compost. If not, follow the details for seed-compost preparation given in Late Winter.

Preparing the soil for planting outdoors

As with early and mid-spring, soil preparation consists of forking and removal of weeds, stones and general rubbish. Also, it is a good idea to add compound fertilizer if you are going to grow chrysanthemums and dahlias or if your soil tends to be the quick-draining type. Plant foods are washed through the latter before the plant roots can absorb them.

Since water plants, water lilies in particular, usually are best planted in pools during late spring, the sites or baskets should be prepared now. You will get the best results if you can plant direct into the pool bottom, but this does mean emptying the pool completely. If you do this, spread a layer about 12.5 or 15cm (5 or 6in) deep of good loam all over the pool base and firm it down well.

Alternatively, you can plant the aquatics which grow under water and up through it in baskets, filling them with good loam put through a 1cm (1/2in) sieve. Bonemeal mixed with this at the rate of 60g (2oz) per container will supply long-lasting food. Prepare this mixture about a week before you intend to plant.

Preparing compost for potting under glass

Potting composts may again be necessary, depending on what you are growing; there are all sorts of plants which can go into their final containers in late spring and you may need a good deal.

Sowing seed outdoors

Seeds to sow in the open are half-hardy annuals, annuals if you are behind (they should produce a display but late in the summer), and biennials for next spring, such as Canterbury bells, double daisies, foxglove, sweet william, Verbascum bombyciferum (mullein) and wallflower. Technically speaking, sweet williams are perennial, but are treated as biennials.

The half-hardy annuals will do best if you can put cloches over the seed-sowing site a few days in advance and then keep the cloches on at night until there is no longer any risk of frost.

If you can get the biennials sown now, they will be magnificent in spring next year as they will have had the longest possible growing season. Seed is sown in a seed-bed and the seedlings thinned and then transplanted to another part of the nursery bed to grow on through the summer until final planting in autumn.

This is the general method of cultivation but there are exceptions and, if you are short of time, it is possible to leave the young plants where they are, provided they have been well spaced out by thinning, until planting time in autumn. Verbascum is not transplanted at all, but planted direct from the seed-bed to its permanent position the spring after sowing. Hollyhocks, which are usually treated as biennials, can also be grown as perennials, though they tend to deteriorate rather rapidly.

Sowing seed under glass

In the greenhouse, seeds to sow now are some of those plants which flower in their pots next winter and spring, such as Primula malacoides and cineraria; cobaea and ipomoea can also be sown for flowering later on this summer and in autumn, as can cactus seed, but the plants from these will not flower until next year at the earliest.

Cacti sown in late spring should germinate within about 7-14 days, but can be left in their seed containers until next spring as they are very slow to grow. Keep the seedlings in a little shade, otherwise the leaves discolour; when young, cacti do not like bright sunlight. Water occasionally but carefully.

Primula seed is very fine, difficult to sow and difficult to germinate. Mix it with sand for even sowing; use a sandy compost and a pan rather than a pot. Cover the seed with a light, fine covering of compost, then cover the pan with a piece of glass and put in a shaded place, making sure that the compost remains moist but not soggy. Temperature should be about 13-16°C (55-60°F). Germination may take several weeks and will be rather erratic when it does start.

Planting outdoors

Towards the end of late spring, you will be able to put out the bedding plants and half-hardy annuals, provided they have been well hardened-off in a frame. There is no point in planting earlier than this unless you have a sheltered garden; too often this kind of plant gets put out early in late spring or even in mid-spring and, although it may not be killed as a result, it will be stunted and slow to grow so that no time is gained.

Choose a warm day, make sure the soil and the root ball are moist before planting and plant in the evening; warm them in lightly and cover with cloches if the temperature is below 10°C (50°F) at night. Spacing depends on the height and spread of the mature plant and can be between 10 and 45cm (4 and 18in).

Hardened-off rooted dahlia cuttings can similarly be planted in spring with cloche protection to start with, as can dormant dahlia tubers which will be just starting to sprout. Spacing can be anything from 23-90cm (9-36in) apart, depending on whether the plants are bedding, the miniature pom-pom type or the giant-flowered decoratives. They will need good, large holes to take the roots or tubers comfortably, and stakes put in now will save a lot of worry later on. Dahlia top growth can be considerable and, although a single stout stake just behind the plant is sometimes .sufficient, they often need several additional lighter ones on the outside, round which string can be tied. The stakes should be rammed firmly into the soil and need to extend at least 90cm (36in) above it for the taller varieties.

Submerged water plants – such as water lilies, pickerel and dwarf reedmace – can be planted now. You can also plant those that grow at the water’s edge, or in mud or shallow water. The submerged aquatics can go into containers, with the crown just protruding above the compost surface. A layer of clean gravel or shingle on the surface will help to discourage fish from exploring the compost and keep the plant in position.

If you plant directly into loam, do it very firmly with the roots well spread out and anchor the crowns with a few stones as an extra insurance against floating. When you run the water in do so gradually, a few centimetres (inches) at a time, with about a week between additions, until the pool is full. Baskets can be lowered straight into their positions in the pool.

There is still time to plant allium and crinum and the last of the gladioli. Pansies sown under glass in early spring will be ready for planting outdoors, after hardening off in a frame; they should begin to flower in late summer. The herbaceous perennials and rock plants grown from seed sown in early spring can also be planted where they are to grow, for flowering, in most cases, for the first time next summer.

Pricking out

By now, the half-hardy bedding plants and annuals sown in mid-spring will need transferring to trays of potting compost; a standard seed-tray will take about 25-30 seedlings.


The cuttings of dahlias and delphiniums may need one transitional potting before planting outdoors, into 7.5 or 10cm (3 or 4in) pots. Chrysanthemum, fuchsia and pelargonium cuttings can also be moved into pots. Fuchsias can go into a final pot size of at least 20cm (8in) diameter for flowering; pelargoniums will be satisfied with a 12.5-15cm (5-6in) diameter. Thereafter they will all remain in pots either in the greenhouse or outdoors in good summer weather.

The final potting for early and late-flowering chrysanthemums needs to be done with more care than usual, as the plants will be in their pots for anything from four to eight months and they will be growing vigorously and flowering profusely. They will need 23cm (9in) pots and J.I. Potting compost No. 3; some gardeners make up a No. 4 mixture, for especially good blooms.

Pots, whether clay, plastic or whalehide, should be well crocked for best results and a little compost put on top of the crocks. The plants should be turned out of their present containers; if they are firmly entrenched a pointed stick pushed through the drainage hole should help to loosen them. Drainage material is removed from the base of the rootball and the plant set centrally in its new pot, so that the surface of the rootball is 2.5-5cm (1-2in) below the pot rim. Compost is then poured in round it and rammed firmly down with a wooden rammer until the container is full. Firm, even potting is very important. Each plant should be given three bamboo canes, about 90-105cm (36-42in) long, spaced evenly round the edge of the pot. Finish by watering and standing the plants in a sheltered place free from the midday sun for a few days, after which they will take any amount of sun.

The half-hardy annuals and bedding plants sown in warmth in early spring and then pricked out may need small pots by now; they can be kept in these pots if the weather is cold and wet, but should be accustomed to lower temperatures ready for planting outdoors late in late spring or at the beginning of early summer.


The hardy annuals sown outdoors last month are the group of plants that will need thinning now. It is important to do it while they are still tiny, otherwise they quickly become straggly, lie about on the soil and never grow into the stout plants that will provide the display expected of annuals.

Hardening off

As soon as freesia seedlings are showing about 1-2.5cm (1/2-1in) of leaf, they can be moved into a cold frame and hardened off for two weeks or so. Then stand them in the open, in a cool, lightly shaded place for the summer; too much warmth will delay flowering.

Half-hardy annuals and bedding plants, whether pricked out or potted, can be put in a frame also, to become gradually accustomed to lower temperatures. Increase ventilation until no protection is supplied, even at night, unless the temperature drops below 10°C (50°F).

Lifting bulbs

The spring-flowering bulbs such as daffodils, crocus, hyacinth and tulips will have finished flowering or be nearly finished and, if they are growing outdoors, can be treated in one of two ways.

If the ground in which they are growing is not wanted for summer plants, they can be left where they are and the leaves allowed to die naturally. The leaves will manufacture some of the food the bulb needs to develop its flower embryo for next spring. Daffodils have actually produced this embryo by the end of late spring and if the leaves are cut off to tidy up the bulbs or because they were growing in the lawn, flowering is unlikely. Such bulbs will often produce offsets instead.

If you have spring bulbs growing where you have planned a display of summer bedding, you can dig up the bulbs as soon as flowering is over and replant them at once in a spare, slightly shaded corner. The technique is to dig a shallow trench and lay the bulbs in at an angle, so the leaves are lying on the soil surface; fill in the trench with crumbled soil and then water if at all dry. This is known as ‘heeling in’. Provided the roots have not been badly damaged in the process of digging up, the bulbs will suffer no harm and will continue to ripen. Once the leaves have withered completely, they can be dug up at any time and eventually replanted. Whatever you do, remove the flower heads when they have died, unless you want the seed.

Resting bulbs

Bulbs growing in the greenhouse which flowered through early and mid-spring will also be coming up to their resting and ripening time. These could include freesia, hyacinth, lachenalia, narcissi and tulip, in fact any of the outdoor spring bulbs which you may have brought on for early display.

Watering should continue while the leaves remain green but as soon as the tips begin to turn yellow, the quantity and frequency of watering should be gradually decreased. When the leaves have completely withered, no more watering should be done. It does no harm to liquid feed with a potash-high fertilizer during and after flowering, but this is not necessary once the plants start to die down. When growth has finished, the containers can be put under the greenhouse staging, laid on their sides for the summer.

Freesias are, however, an exception. These should be removed from the compost; you will find, when doing this, that the corms have buried themselves much deeper than the seed was originally sown. There will be one large and several smaller corms to each plant and, unless you want to go into the business of freesias as cut flowers, it is best to keep the largest corms only and do away with the remainder. You could grow them on, but it takes two to five years to produce flowering corms, depending on their size, and you will need a great deal of compost and space if you do decide to raise freesias in this way.

Clean the corms you are keeping of compost, roots and dead leaves, lay them in a single layer in a seed tray and store them in the dark, ideally in a temperature between 19 and 30°C (68 and 86°F). Too high a temperature or storage in sun results in ‘petrified’ corms; too low a temperature produces ‘sleepers’, which do not flower but which also do not die. They will grow normally if planted the following summer, having missed a year.

more on Flower Garden Tasks in Late Spring …

29. August 2011 by admin
Categories: Flower Garden, Types of Gardens | Tags: , | Comments Off on Late Spring Jobs in the Flower Garden


Get every new post delivered to your Inbox

Join other followers: