Most ferns do best in a situation where they are protected from strong winds, extremes of temperature, and excessive dryness.
Ferns growing in containers are usually best placed on a shaded veranda or patio or underneath some large trees where they will only receive filtered sunlight.
Ferns growing in the ground are normally best with moist soil in semi-shade or full shade. If there is any likelihood of the ground drying out, heavy organic mulch is recommended.
Greenhouses may be needed to provide shade protection for growing ferns, particularly in warmer climates. Shade houses need to have shade cloth (or something else) on the sides, as well as on the roof, to break strong winds.
Adequate ventilation is generally important to minimise fungal infections. This can be achieved by not placing plants too close together, and by ensuring that there is some air movement, particularly through greenhouses. Too much air movement, however, can also be a problem.
Soils and Potting Mixes
Ferns are only as good as the soil they are growing in. If you want quality plants you must use quality soils and potting mixes. Ferns are generally adaptable as far as soil type goes, but a soil that is well-drained, well-aerated, has a reasonable pH, has high organic matter and good moisture-holding capacity is preferred by most. For container growing of ferns, or even in specially prepared beds, potting mixes can provide an excellent substitute for the fern’s natural soil type.
Before planting ferns out into the ground, the soil must be properly prepared. Remember, the soil should be high in organic matter and reasonably well-drained. Most soils will benefit from large quantities of manure and compost being dug in before planting. A reasonable approach would be as follows:
1. Dig over (or rotary hoe the soil first)
2. Spread compost, wood shavings or fine shredded pine bark to a depth of 200mm and dig this in to a depth of 400mm
3. Spread well-rotted poultry or cow manure over the area to a depth of 50mm and dig in to a depth of 200mm
4. Water well and leave for at least two weeks
5. Spray any weeds which begin to germinate with Zero or Roundup weedicide, and leave for another week
6. Plant the ferns and cover with a surface mulch 100mm thick
Most ferns do need to be fed from time to time, though as a general rule they are more susceptible to fertiliser burn that many other types of plants.
If you stick to the following recommendations you are unlikely to have any major problems:
- Use fertiliser twice as often as recommended, but at half the recommended rate.
- Never get the fertiliser on the foliage – always apply it to the soil under the fronds.
- Don’t dig the fertiliser in (ferns are happiest not having their roots disturbed).
- Water the fertiliser in well as soon as it is applied, to prevent concentrated lumps
making direct contact with any exposed surface roots.
- Organic liquid fertilisers such as Maxicrop plant food, Seasol, Nitrosol or Garden
Party are ideal for ferns, being less likely to burn than inorganic fertilisers.
- Slow-release fertilisers such as pelletised fowl manure or Osmocote are also excellent for ferns.
- Check what has been written about the variety of fern you are dealing with before
you feed it. Some varieties should never be fertilised. There are other varieties which require heavier feeding than the average fern. Watch the fronds of the heavy feeders - if they go pale in colour, or if the growth rate slows, you can increase the feeding up to 30%. However, in cooler climates yellowing growth in winter may be a sign of a response to cooler temperatures and slowing of growth, so in this case do not feed them until the warmer weather returns
What Nutrients Does a Fern Need?
All plants need a range of different nutrients not just to grow, but also to remain healthy.
The following nutrients are needed in large amounts: nitrogen, phosphorus, potassium (also called potash), calcium and magnesium. These are called major nutrients.
A large number of other nutrients are needed in much smaller amounts including iron, sulphur manganese, boron, zinc, copper, molybdenum, chlorine, cobalt and sodium. These are called minor nutrients.
Most soils will contain all that a plant needs of calcium, magnesium and the minor nutrients. Fertilisers therefore are usually designed to supply mainly nitrogen, potassium and phosphorus - the nutrients most commonly needed.
The fact that a nutrient exists in a soil does not necessarily mean that the plant can use or absorb it. If the pH (level of acidity) is wrong, the plant can have a lot of difficulty absorbing some of the required nutrients even though they are in abundant supply, for this reason the soil pH is an extremely critical factor in growing some types of ferns. You can measure pH with a pH test kit available from most good nurseries or garden centres. (The chemical test kit is more accurate than inexpensive pH test meters). These kits usually have excellent instructions not only on how to use them, but also on how to adjust the soil pH after you have tested it.
Is Your Fern Underfed?
If a fern is underfed, the foliage will often become lighter in colour. If the older fronds become very pale, the fern probably has a nitrogen deficiency, in which case a good feed may help. Other symptoms of nutrient deficiency include loss of vigour in the growth and increased susceptibility to disease.
Is Your Fern Suffering Fertiliser Burn?
In extreme cases the youngest, most tender foliage will burn at the tips if too much fertiliser has been applied. If you dig up a few young roots and examine the growing tips, fertiliser burn will often show as a discolouration or dying back on the growing root tips. (Over watering can result in similar symptoms). If the plant is in a pot, simply remove it from the pot to make a quick examination of the roots.
The only way to treat a plant which has been given too much fertiliser is to leach the fertiliser away. For a container-grown plant, extra watering may help. For a plant in the ground, often only the passage of time will help it to gradually recover. (Remember it is easier to put fertiliser in than take it out).
Ferns are pruned for the following reasons:
1. To remove dead or diseased fronds. These look unsightly and detract from the overall appearance of the plant, more importantly, diseased fronds encourage disease to spread to healthy parts of that plant, or other plants nearby. Dead or diseased fronds should be removed or burned.
2. To control the size of the plants. Large ferns can spread and impose on other parts of the garden. In such cases they are pruned back simply to control their size
3. To promote new growth. If older, perhaps marked or unsightly fronds are removed, a flush of new, lush growth will be stimulated; you may choose to take such action, to bring your plants to looking their best for a particular occasion.
Whenever you prune, be sure to use sharp tools, and always cut the leaf stalks right back to the base. A clean cut will heal, a rough cut is likely to become diseased.
For the vast majority of ferns, there are four main advantages to mulching:
1. It keeps the roots cool in warm weather
2. It keeps the soil moist during the drier part of the year
3. It controls weed growth which might compete with the ferns
4. It replenishes nutrients in the soil
There are many different types of mulches available, e.g. horticultural fabrics, gravels, stone, organic mulches, but only the organic mulches will provide all four benefits listed above.
The best organic mulches for ferns are peat moss, sphagnum moss, compost, leaf litter or something similar. Unfortunately, these are also the most expensive or more difficult to obtain materials. Less expensive alternatives are shredded pine bark, red gum chips or wood shavings. These materials should not be used too fresh, they need to be weathered for at least three months in wet conditions to eliminate toxins.
Ferns will respond well to mulching at least once annually, in early spring. The mulch should be spread to between 10 and 20cm thickness.