Tips for Naturalizing
If a bulb plant is to develop to its full potential, it must be provided with good growing conditions and a suitable niche in the landscape where it can remain undisturbed without the need for its foliage to be prematurely removed. It is important for bulbs to retain their foliage after bloom until the leaves die back naturally, and that they are able to enjoy an uninterrupted cold period.
Crocus, for example, will thrive for years if planted in manicured grass with somewhat dry soil. But the foliage must be allowed to develop fully, the grass should not be mowed until the crocus leaves have died back. Even though the grass may still be dormant, there is always the urge to get out the mower and to cut off the foliage immediately after flowering is over, but this should be avoided. The foliage must remain for the bulbs to re-charge themselves through photosynthesis. It is a small price to pay for the beauty and joy of the following year’s colourful spring display.
Once flowering is over, foliage develops more rapidly and often seeds are formed. For the majority of bulbs like Chionodoxa and Scilla it is important that they are allowed to mature and ripen naturally, for when distributed in moist rich soil they will germinate freely and rapidly enlarge the colony.
Exceptions: not all bulbs, once planted can be left to their own devices. Some do not propagate freely nor continue with a satisfactory show of flower. Hyacinths and many of the hybrid tulips do not perennialize well, for example.
There are many locations that can successfully accommodate flower bulbs. Ideally, plantings should be of sufficient size to make a viable display and situated in positions where they can be easily viewed from any angle. Large grassy areas are especially well-suited. In addition, broad mixed borders and shrub plantings all lend themselves to permanent bulb plantings. A wooded area can be considerably enlivened by the addition of sweeping plantings of shade-loving species. Amongst these are Allium ursinum (ramson), Anemone nemorosa (wood anemone), Anemone ranunculoides, Erythronium dens-canis (dog's-tooth violet), Corydalis cava (bulbous corydalis), Corydalis solida, Arum italicum, Fritillaria meleagris (snakeshead fritillaria), Galanthus nivalis (common snowdrop), Hyacinthoides non-scripta (bluebell), and Ornithogalum umbellatum (common Star of Bethlehem).
Where a less natural-looking planting is appropriate, low, daisy-like Anemone blanda is available mixed or in separate colours of white, pink and blue, or Spanish bluebell can be used instead of the native species. In some cases the more alien species grow better than those which are native.
The soil must be carefully considered when planning to plant flower bulbs. Moisture and humus content as well as acidity or alkalinity (pH) all play an important part in the success of the venture. Drainage should be good and where the humus content is poor, the soil should be improved by the addition of well-rotted organic matter. Heavy loam and clay soils especially benefit from this treatment. The acidity/alkalinity (pH) of the soil should ideally be between 6 and 6.5. It can be increased by adding garden lime or lowered by the addition of peat (which has a very low pH of 4).
Most soils do not require special treatment in order to be suitable for naturalizing bulbs. Of course, this is to some extent dependent upon the bulbs that you propose growing and the type of soil and conditions that prevail. Crocus, grape hyacinths and narcissi are particularly suitable for larger grassy areas such as medians, slopes and the areas in front of shrubs. They are very useful for extensive sites where it is possible to plant mechanically.
For long-term blooming year after year, feed perennialized bed plantings regularly. To obtain best results, use fertilizer several times during the growing season. The first application should be made about one month after planting. Then again immediately before and after flowering. If it is only possible to feed on one occasion, this should be directly after flowering. An inorganic fertilizer can be used that has an NPK 12-10-18 (2 kilograms per 100 square meters, or just under 4.5 lbs. for every 120 square yards per application) or a mixture of organic fertilizers or a timed-released fertilizer can also be used. These should be applied just before or during a rain shower so that they become available soon afterwards. Granulated dried cow manure can also be used and is very easily applied. Covering bare soil with a generous mulch of stable manure or compost is usually only practical for small areas.
For naturalized plantings in the landscape, such as daffodils, follow this regime: During the autumn, apply an organic fertilizer or use a timed-release bulb food. We have stopped recommending bonemeal in Canada as the new formulations smell just like bones, and dogs go crazy digging in spots where bonemeal has been applied. A quicker acting artificial fertilizer can be used during late spring when the blossoms are beginning to fade, but the foliage is growing vigorously. Without feeding, flower bulbs go steadily into decline after their first year, very few continuing from year to year.
Mowing and Maintenance of Naturalized Bulbs in Grassy Areas
Once a group of flower bulbs has become successfully naturalized, attention should be paid to the grass in which they are growing. Inevitably, if all is well, grass will provide considerable competition for the bulbs. This is especially true during the 6 to 8 weeks following bloom, when the bulb foliage and grass must be left to go about their business (photosynthesis) untouched. Once foliage of the bulbs has died away naturally, grass and bulb foliage should be regularly mown to within a few inches of ground level. Without regular mowing, naturalized bulbs will suffer and may begin to die out. Regular aerating in the autumn will assist both the grass and the bulbs.
Some bulbs, notably Chionodoxa, Scilla and Eranthis depend upon seeds for propagation. These seeds must have ample opportunity to ripen properly before cutting begins. As soon as the seeds fall from fruits, mowing can start. (This is usually 6-8 weeks after the flowering period).