Planting a Streamside

A streamside is a very different prospect from any other aspect of a water feature, for not only must the planting be tasteful and properly executed, but it must also tolerate occasional inundation and periodic drying out.

Erosion should be uppermost in the gardener’s mind, when thinking about when and how the streamside is to be planted, especially if the stream is uncontrollable with a flow rate that is subject to the whim of nature. An artificial stream is an altogether different proposition, and much of the advice given for planting a bog garden is applicable.

 

PREPARING THE BANK

With an artificially constructed stream, the method of preparing the soil will be similar to that required by a bog garden, although if the banks are steep, some account must be taken of the fact that soil may slip into the water following heavy rain. Prevention of this erosion does not differ from the treatment advocated for the natural stream.

With a natural streamside, it is an advantage to have a covering of vegetation, even if this is of weeds. Plants of any kind, which have become established on the banks, will hold them together and prevent erosion. This factor must be taken seriously, even with a tiny stream or ditch if it has uncontrollable water levels. The substantial cultivation of a streamside can lead to rapid erosion, so allowing the roots of any vegetation to remain and bind the soil together is a sensible move.

Modern herbicides, in which the active ingredient is glyphosate, are marvellous. Not only are they completely harmless to aquatic life, but they also ensure the positive destruction of any weeds treated. Glyphosate works on contact with green leaves, being absorbed into the plant’s sap stream and translocated throughout, preventing the weed from producing essential protein and killing it from within. The great advantage of this, apart from a total lack of contamination of the soil, is the fact that, while the tops of the plants die away completely, the root systems remain intact as a fibrous web throughout the soil. This effectively prevents serious erosion of the stream banks.

The temptation to cultivate and prepare the soil, once the green herbage has died back, should be resisted. This would be fatal, as disturbing the fibrous mat of roots would undo the benefit of the decomposing weeds’ presence. A generous mulch of well rotted organic matter would be beneficial, however. Not only will this improve the humus level in the soil, hut it will also smother any emerging weed seedlings. These are almost certain to appear once the existing weed cover has been removed.

The ideal time to kill off the weed cover is during late summer. Then the mulch can be applied and the streamside remain unplanted for the winter. Occasionally, the mulch may be scoured out at high water level, particularly in the turbulence following a snow melt, but the soil bank below should remain firm. Any loss of mulch can be redressed in the early spring and planting commenced. The weed root network will remain effective for about nine months after spraying, so planting young plants in the spring is ideal. They will grow away strongly, their root systems replacing the slowly decaying roots of the weeds by mid-summer.

Do not plant a natural streamside during the winter months. Although periodic flooding may not wash away the plants completely, it can cause disruption. Even during the spring, it is preferable to use pot grown plants, as these will be more stable if unexpected inundation occurs. If you have a river bank to plant, rather than a stream, pushing a large wire staple through the pot-ball of each plant and into the soil below will provide extra security.

The arrangement of plants on a streamside is very much a matter of taste. Be conscious of plants that will seed freely and may make themselves a nuisance, keeping them away from the water’s edge. Water is a fine distributor of seeds, and a streamside can quickly become engulfed in water forget-me-not or mimulus if the plants are allowed to seed unrestrained by the water’s edge, especially when planted upstream. Care should also be taken not to introduce any plants that might be transported to places further downstream, where they could become a nuisance and affect the native flora. Seeds and pieces of plant like Mimulus ringens, which root easily as cuttings, should be used responsibly.

 

THE GRASSY BANK

Although many may wish to see the streamside as a riot of colour, in some cases, it will be very effective if grass banks extend to the water. Achieving this may not be as simple as one might imagine, however.

Whether you use turf or seed, the banks must be cultivated, and a light forking is the minimum requirement. Ideally, any existing weed cover should be killed off with a glyphosate based weedkiller to minimize the prospect of serious erosion taking place. As an additional precaution, protect the most vulnerable areas with fine-mesh garden netting. Professional landscapers use custom made erosion matting, which is pegged down to the soil, hut this is difficult for the amateur to obtain and garden netting is the next best thing.

Peg the netting to the ground, covering the bank from below the minimum water level to above the maximum expected level. Then lay turf on top, or spread fine soil over it and sow grass seed. Most grass seed mixtures are suitable for a streamside, but one containing a proportion of rye grass is preferable.