If you're having problems with Swiss chard, it could be due to any number of factors. Here are the most common ones.
Insects tend to leave Swiss chard alone unless the plant is stressed by dry weather, and then the major problems are with aphids.
Aphids and ants always seem to go together, and ants will herd aphids to where they want them. Plant something aphids love (such as nasturtium) or something ants love (like thyme) next to your chard or release ladybugs in the area if aphids cause serious problems for you.
(Caveat: apparently ladybugs aren't as good for long-term control of aphids as people think)
Another insect that occasionally causes problems with Swiss chard is the leaf miner. This tiny whitish caterpillar will chew tunnels through your chard leaves, which should be removed.
If leaf miners cause big problems in your area, use a light row cover over your plants during the spring.
Row covers will solve problems with other insects such as grasshoppers or cabbage moths, which will on occasion eat chard.
Snails and slugs will chew holes in chard leaves and grooves in the ribs. Over-watering will encourage them to snack on your chard, so let the soil dry out before you water. Trap them, hand pick and dispose of, use an iron phosphate based slug control product, or surround your chard plants with crushed eggshells.
Deer will eat chard, but usually only in the autumn, after other foods they like better are gone.
Many diseases can cause problems with Swiss chard -- here are the most common ones:
Cercospora leaf spot is a fungal disease that causes light brown patches surrounded by purple halos on Swiss chard, beet and sometimes spinach leaves, and is most often seen in warm, rainy climates.
Space plants out so they don't touch each other and remove affected leaves as soon as you see them.
Viral diseases can cause new leaves to be small or distorted, but plants can sometimes outgrow the infections. Pull out the plants that show no signs of improvement after a few weeks and discard them.
Downy mildew is encouraged by watering too much or having your chard plants clustered very close together. Thin out some of your plants to improve the air flow around the leaves and direct the water right at the soil.
If a flower stalk develops, cut it off, unless you like the look of it in your garden or want to save the seeds.
Bolting doesn't mean the end of the season like it does for other greens -- chard will continue to make edible leaves all through the year.
While the leaves may be more bitter in summer, they are fine for cooking and will sweeten as the weather cools off.
If your summers are more likely to roast your chard than anything else, plant in the shade of taller plants such as trees, shrubs, or tall flowers.
Planting on the north and east sides of buildings and taller plants (or south and west in the Southern Hemisphere) will keep your chard shaded during the worst of the heat.
Bitterness in Swiss chard is entirely due to drought, and dry plants are much more likely to bolt, so plant your chard close to a water source such as a downspout, roof drip line, or faucet if possible to make it easier for water to get to it.
(This will make it easier for you to water your chard in the middle of summer too!)
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