How to Keep Plants Healthy

Plants, like people, are much less susceptible to disease if they are living in naturally healthy conditions. Keep your plants healthy with these simple tips and tricks.

Step 1: Install Traps and Barriers

Garden Mates

Garden Mates

Companion planting is a very old but largely unproven method of natural pest control. Traditional companion plants such as these marigolds may deter flying pests, including whitefly, and their root secretions are thought to inhibit soil pests and weeds.

©2008, Dorling Kindersley Limited

2008, Dorling Kindersley Limited

Companion planting is a very old but largely unproven method of natural pest control. Traditional companion plants such as these marigolds may deter flying pests, including whitefly, and their root secretions are thought to inhibit soil pests and weeds.

Although traps and barriers require some effort to install, in many cases they provide full protection against pests.

  • Large mammals can be fenced out of the garden. Fences for deer should be at least six feet high all around the garden; rabbit barriers must be three feet or more high and sunk a further one foot beneath the ground to prevent the rabbits from burrowing under them.
  • Birds will not be able to feast on your fruit trees and bushes if you surround them with netting or fruit cages. Although these barriers can be costly, they do provide peace of mind.
  • Small mammals can be trapped, but this is often best left to the professionals. It is not easy to trap moles, squirrels, and rabbits. Trapping mice is straightforward, but rats are wilier. Poison bait, carefully placed to avoid harm to pets, wildlife and children, is the best option.
  • Slugs and snails find crossing copper very uncomfortable; bands of copper around the top of a pot should stop them in their tracks. However, they will seek out a bridge across the barrier, so you need to be watchful. In beds and borders, rings of sharp materials that slugs and snails may find scratchy to cross can be used around vulnerable plants. Poultry grit, crushed eggshells, and cocoa shell mulch give some protection; however, they are far from foolproof, and commercial granule barriers may be more effective. Again, a leaf bridge will undo all your work.
  • Ants and other pests can be prevented from climbing prized plants by collars of aluminum foil turned outward; these need refreshing as the plants grow. Bands of a plant-friendly grease can be applied to the stems of trees to prevent wingless pests, such as female winter moths, from ascending. Fruit trees, including crab apples, are most likely to benefit from this. If the tree is staked, you must grease the stake too, or it will provide a bypass for pests up to the crown of the tree. 

If you don’t like the thought of trapping the creatures in your garden, ”companion planting,” which helps to deter them, is always an option. For example, not only are marigolds (Tagetes) said to keep flying insect pests off plants such as roses, but their root secretions are thought to help prevent soilborne diseases and pests, such as nematode worms.

Step 2: Follow Good Gardening Rules

Ward off pests and diseases in your garden by following a few simple rules:

  • Protect plants against the cold, wind, and drought; they are especially vulnerable when newly sown or planted. Spread out roots and carefully secure them in well-prepared soil, avoiding excessively deep planting. Faults here may be fatal, but not before years of disappointing growth.
  • Rotate bedding plants to avoid a build-up of pests and diseases; don’t plant them in the same place in consecutive years. n Weed regularly to reduce pest and disease problems. Clean up fallen leaves, fruits, and dead wood. Do not compost or recycle infested material; remove it by burning it or putting it out for collection with yard waste.
  • Avoid damage to plants—often caused by mowers, string trimmers, and by pruning—by using tree guards and edging strips on lawns. Damage opens up the way for disease and rot.
  • Avoid dense planting to increase airflow between plants; thin any crowded growth by pruning. The lower humidity levels should help reduce molds and rotting. Indoors, too little humidity is more likely, encouraging red spider mite and whitefly attacks. It can be countered by misting and dampening plants frequently, and by standing plants in trays of moist gravel or inside larger pots of damp moss.
  • Avoid overwatering, as permanently wet roots can lead to root rots and dieback, whereupon even mildly harmful fungi, such as coral spot, can cause great damage.
  • Avoid underwatering, as dry roots and irregular watering weaken plants, encouraging powdery mildew.

Step 3: Team Up With Natural Allies

Pond Pointers

Pond Pointers

A garden pond will encourage a range of beneficial wildlife. Make a “deep end” 36 inches in depth for aquatic creatures to escape freezes, and a “beach,” so small animals and birds may approach the water safely. 

©2008, Dorling Kindersley Limited

2008, Dorling Kindersley Limited

A garden pond will encourage a range of beneficial wildlife. Make a “deep end” 36 inches in depth for aquatic creatures to escape freezes, and a “beach,” so small animals and birds may approach the water safely. 

Most insects are not pests – some, often seen in the vicinity of damaged plants, actually only take advantage of damage that has been made by the weather or by another pest. Some insects only cause problems under certain circumstances:

  • Ants are a nuisance in lawns and may loosen the plants’ grasp on the soil; counter this with watering, raking and soil firming. They also cause problems when they “farm” aphids for their honeydew, protecting them aggressively from predators so that large and harmful colonies build up on vulnerable plants.
  • Woodlice, centipedes and millipedes are excellent “recyclers” of plant debris, but might occasionally nibble at holes made by slugs and other pests, or damage delicate seedlings. Encourage them to go elsewhere by clearing away debris.
  • Bees are vital for pollination, and therefore are among the creatures that should always be spared - even the leaf-cutting bees that take an occasional bite from plants.
  • Wasps can be a nuisance throughout late summer, but before that they will obligingly prey on other insects. You should only destroy their nests if you really have to - for example, in a family garden.

Step 4: Release Biological Controls

Instead of using chemicals, you can release nematodes, insects or mites that prey on certain pests. These controls are most effective in greenhouses and conservatories - outside, they are likely to dissipate. When using natural predators to control pests, don’t also use synthetic insecticides, and ideally only use those based on fatty acids or plant oils that leave no residues. 

Biological controls for vine weevils and slugs are watered onto the soil. For slugs, apply from spring to early fall. The control for vine weevil is best used in containers in later summer before the grubs do much damage. Both work best in open-structured soil. Controls for red spider mite and whitefly are effective in the greenhouse as long as they are used before the pest becomes too numerous. 

It’s usually best to buy biological controls by mail order. A few garden centers stock them, but as they are living creatures, they are not easy to store.

Step 5: Encourage Pest Predators

Attract beneficial creatures into your garden by providing them with food and shelter. Features to tempt wildlife are generally inexpensive, many are attractive, and those that are less so are fairly unobtrusive. Gardeners can also create a wild corner of the garden where grasses and plants are left to grow unrestrained and allowed to stand over winter. Include a range of native species, and only use pesticides when and where they are really necessary.

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