Poisonous plants in California are not that many, luckily – the main ones are poison hemlock, oleander and poison oak.

Poisonous Plants in California

How do you know which plant is poisonous? If it poisons you, what do you do once you develop symptoms?

Continue reading to know the answers to these and so much more!

Dangerous and Poisonous Plants Commonly Found in California

Since there is livestock grazing in the fields, it is essential to know which of the plants growing in their grazing area are poisonous. These plants are not restricted to only the fields but are commonly found in our backyards. When consumed or touched, these plants may have lethal consequences for humans and animals alike.

1. Poison Hemlock (Conium Maculatum)

The plant is a biennial that belongs to the Apiaceae family and is native to Europe, Western Asia, and North America. It is included in the list of ASPCA poisonous plants.

Poison Hemlock herbaceous weed

It grows well near water, waste areas, roadside, and cultivated fields. Furthermore, it is a herbaceous weed that is highly poisonous, and even the slightest amount is toxic not only to humans but also to wildlife and livestock. Check out our list of plants that look like Poison Hemlock and learn how to identify them.

– Growing Season

The plant is grown all year round and has invasive growth. Its average height is 4 to 6 feet, and its compound leaves are up to 18 inches long and 12 inches wide.

Its flowers are tiny and white and are shaped in umbrella-shaped clusters on the tips of the branched stems. During its first growing season, it does not have a fast growth rate and overwinters in temperate climates.

– Specific Needs

The plant has little light needed. A considerable amount is enough to help it thrive. It even does well in filtered sunlight or shaded areas, meaning you will likely find it growing everywhere. The biennial does not have specific soil preferences; it does well in sandy, loamy, and clay soils, with a pH between mild acidic and mildly alkaline.

It shows aggressive growth with a consistent water supply, which is why it grows aggressively along river banks and streams. However, a small amount of water is enough for it to reach its potential height. Fertilizers rich in nitrogen content encourage its growth. It self-propagates through seeds that let go of the plant when it matures.

Symptoms of the plant include trembling, digestive tract burning, dilated pupils, increase in salivation, irregular heart rate, trouble in speaking, muscle fatigue, and unconsciousness, and under severe consequences, respiratory failure and death. It is wise to seek medical help if the reaction worsens daily.

2. Oleander (Nerium Oleander)

This toxic plant, known as Jericho rose or rose laurel, is an evergreen perennial rounded shrub but can be grown as a single or multi-trunked small tree. It belongs to the Apocynaceae family and is native to Southern Asia and the Mediterranean.

Oleander irritate the skin

It is extremely toxic even when consumed in a small amount. The plant bears a poisonous flower in California. The slightest touch is enough to irritate the skin. Pain in the abdomen and blurry vision are some poisoning symptoms. It is one of the most poisonous bay area plants and one of the deadliest poisonous plants in Los Angeles.

– Growing Season

The blooming period for Oleander starts in spring and lasts till the end of summer. It also flowers in early fall and all year round in warmer climates. It has an average to fast growth rate, up to 1 to 2 feet per year. The mature plants grow quickly and easily from the base if damaged by the cold.

It grows up to 19 feet and is as wide as 10 feet. The flowers vary from white to dull yellow, peach, salmon, pink, and deep burgundy. Its leaves are leathery, dark green, line-like up to 7 inches, and barely an inch wide.

– Specific Needs

The plant prefers to grow in full sun. Its leaves are less dense when it is growing in partial sunlight. Drought, heat, and wind does not stop it from growing.

It prefers well-drained, moist soils but quickly adapts to all kinds of soils. If given a choice, it likes an alkaline pH soil but would not say no to neutral or acidic pH soils. Furthermore, Oleander does not self-seed. Rather it propagates through stem cuttings, meaning it only propagates on its own if you plan on doing it.

The plant’s flowers, stems, and leaves are toxic if consumed. Some symptoms include low blood pressure, blurry vision, diarrhea, and even death. When experiencing any of these symptoms, visit your nearest medical facility.

3. Poison Oak

The oak plant is a perennial that belongs to the Anacardiaceae family. It is native to North America.

Poison Oak poisonous plant for dogs in California

It is commonly found growing near the coasts of California and is one of the most poisonous plants in southern California and is a poisonous plant for dogs in California. An oily sap coming from the plant is responsible for irritating the skin and causing allergic reactions. Check out our list of plants that look like Poison Oak and learn how to identify them.

– Growing Season

The plant shows optimal growth in February and March but grows all year round. It has a fast growth rate, and the stems grow invasively after two months of planting.

It is a low-growing shrub that reaches its highest height of 10 feet. The flowers are five-petaled dull yellow or white, while the leaves are lobed or toothed with round edges. The colors of the leaves also vary from plant to plant.

– Specific Needs

The plant grows under the full sun but tolerates partial shade too. It prefers sandy, fertile, and well-draining soil over heavy soil. Furthermore, it only needs a little water when growing in the shade.

It takes a great deal of water to grow. The shrub is commonly found growing near water. It does not self-propagate, is not invasive, and propagates vegetatively through rhizomes and seeds.

After being exposed to the plant, you may experience a condition called contact dermatitis. The symptoms take 24 to 72 hours after exposure to crop up. The condition appears in the form of bumpy blisters that itch. 

Apply to rub alcohol to the exposed parts of your body and wash your hands with dishwashing soap and cold water. Moreover, plenty of herbicides are available in the market that can be used alone or in combination to control the spread of the plant.


You might be growing one of these plants without knowing how poisonous they are for you and your pets. But do not worry, as we have the answer to all your questions. Before jumping onto the identification of the plant, always remember the following points from the article above:

  • If you have developed itchy blisters on the exposed parts of your body, you have likely been in contact with the oak one to three days ago.
  • The most common plant in California is oleander, so consider it your first guess.
  • Oleander has the most beautiful flowers in shades ranging from white to burgundy.
  • Different plants have different symptoms, so it would be wise to keep an eye if you suspect them.

After learning more about these plants, can you identify – and avoid – them?


  • https://www.nps.gov/articles/000/pacific-poison-oak.htm
  • https://hgic.clemson.edu/factsheet/oleander/
  • https://www.ars.usda.gov/pacific-west-area/logan-ut/poisonous-plant-research/docs/poison-hemlock-conium-maculatum/
5/5 - (5 votes)
Evergreen Seeds