Why Are My Greenhouse Plants Dying?

Why Are My Greenhouse Plants Dying?

In Plant Problems by Ana M

Although greenhouse structure lets you to extend the growing season, it can be quite challenging to create the perfect environment to grow plants. You need to consider how are you going to grow plants – in pots or directly in the ground? Are you going to grow shade loving plants?

The list of questions that you need to ask yourself goes on and on. Think about organizing your greenhouse before buying plants. You don’t want to invest money in a collection of plants that will be dying after you moved them to a greenhouse.

The most common reason why greenhouse plants are dying is allowing rapid temperature changes inside the structure. Maintaining stable temperature by ventilating on a hot day and preventing excessive cooling is a key to successful growing inside the greenhouse.

If you just saw nice plants in the nursery and brought it to the greenhouse on the same, unfortunately, it is very likely that the plant is going to die. Growing in a greenhouse requires a throughout planning. You need to research plant’s needs before hand and only purchase plants that you can grow in the conditions that your greenhouse can offer.

The most common reasons why greenhouse plants are dying:

  1. Inadequate Watering
  2. High/Low Humidity
  3. Poor Soil
  4. Wrong Lighting Requirements
  5. Too much or too little fertilizer

In this post you will find out how to determine if your greenhouse plants are dying. Also, we will tell what symptoms can point out the underlying cause of plant’s problems. Moreover, you will learn how to fix these problems and what you can do to prevent them in the future.

1. Inadequate Watering

Sings and Symptoms: The most common sign of overwatering is that plant leaves are turning yellow. Soggy soil and fungus are also wide symptoms of giving your plants too much water. On the other side, if the leaves look droopy and about to fall off, the plant is underwater.

Causes: It is very easy to give too much or too little water to plants in a greenhouse. That is because of the humidity levels. We will talk about it in more details later on. Apart from humidity levels, poor drainage is the most common cause of both overwatering and underwatering.

Inadequate watering is one of the reasons why are Greenhouse Plants Dying

Lack of organic matter or high content of clay in the soil can result in water not draining properly. It is just going to sit on the surface around the plants roots. That is the most common cause of wilting and dying of cucumbers, that are very popular greenhouse plants.

How to stop plants from overwatering?

Solution: To avoid the problems with watering you need to water plants early in the morning. That way you can observe how dry they get during the day and give more water if needed. To avoid overwatering, on a cloudy day water in the morning and check later in the evening if plants need more water.

Also, keep in mind that in spring when looking after seedlings and young plants you need to water more frequently. The same applies to mature plants growing in a greenhouse during hot summer months. However, always check watering requirements to meet individual plant needs.

watering plants in a greenhouse

For example, if you are growing cacti, they like to have a dry rest for a week. Then you can water them again. To successfully grow ferns in a greenhouse you need to let the soil be moist for a while and wait for it to get dry. Then you can water ferns right away.

Prevention: You need to learn how to water plants in a greenhouse. Think about installing watering system, for example, drip irrigation works well in a greenhouse. Moreover, to prevent problems with poor drainage you need to install greenhouse flooring. Finally, make sure that you are using the best soil for greenhouse plants.

2. High/Low Humidity

The ideal humidity in a greenhouse should be around 50-70% relative humidity, however, 60-80% is usually acceptable. Relative humidity is the measure of the amount of moisture in the air.

Sings And Symptoms: If the plant leaves are crisp, it means that air in the greenhouse is dry and humidity is low. On the other hand, if plant rots, then the relative humidity is too high. Also, high humidity can lead to spread of mold spores and result in diseased plant.

Why Does Greenhouse Steam Up?

Causes: Humidity (moisture in the air) is the irreplaceable part of greenhouse environment. As you know plants take water from the soil with roots and then evaporate that moisture in the air around them through leaves. That process is called transpiration.

Plants use stomata on the undersides of their leaves to transpire, in simple words ‘to breathe’. So, when temperature is too high, a plant closes its stomata to reduce water losses and cools itself down. So, when relative humidity is too low and the high temperatures stay for a long period of time, plant starts to suffocate and is dying of thirst.

Alternatively, when relative humidity is too high which results in a dry air, the water cannot evaporate from the leaves surface. Moreover, plant roots can’t absorb nutrients from the soil. If high humidity levels stay for a prolonged period, mold spores can easily spread causing plant to rot.

How to manage humidity in a greenhouse?

Solution: You need to monitor the humidity in a greenhouse at all times! Get a hygrometer to observe if humidity is too high to prevent the condensation in a greenhouse. Temperature directly affects humidity, so you need to aim to keep the stable temperature in a greenhouse without spikes during the day and sudden drops at night.

greenhouse misting system
Install misting system in a greenhouse to increase humidity

Prevention: Installing misting system in a greenhouse is a great solution to increase humidity for humidity loving plants like African violets. Moreover, invest in automatic vents openers that will open vents when temperature rises. Also, sort the plants regarding their humidity needs, so you can create ideal micro-climate for plants with the same needs.

3. Poor Soil

Don’t underestimate the importance of good soil for plant growth. DO NOT use garden soil in a greenhouse or for filling up the pots! It is not suitable and will result in greenhouse plants dying.

Sign and Symptoms: That plant that is growing slowly or if it is not growing at all indicates on the problems with soil or potting mix. If you are keeping plants in large containers, you will also notice that container became too heavy to lift or move.

Why does soil get compacted?

Causes: Poor soil can easily get compacted which can kill the roots as they don’t get enough water as well as air. Even though your soil is loam, if you keep growing same crops in the same spot over again, it can loose fertility and attract pests. Finally, potting mix decays and becomes mucky after some time.


Solution: Never use garden soil or old potting soil! Change the potting mix in pots or at least swap top inches with a new mix every one or two years. When growing in a greenhouse, build a raised bed and fill it with 30% peat moss, 30% vermiculite and 40% compost. Soilless mix prevents problems with soil-borne diseases and pests.

Prevention: Test your garden soil first to find the content of clay, loam and sand. Amend the soil with store bought or homemade compost. I recommend building a raised bed to prevent problems with pests and diseases. Also, practice crop rotation. For example, grow heavy feeders after onion and garlic but don’t plant beans and peas.

4. Wrong Lighting Requirements

Lighting requirements are often overlooked by greenhouse gardeners. Although plants need from 6 to 8 hours of diffused sunlight, at early growing stages plants benefit from direct sun rays. Also, some plants prefer to grow in shade.

Signs and Symptoms: Plant burned by too much sunlight have blanched leaves. On the other hand, if the plant is not getting enough light, it becomes spindly and stretched out. In some extreme cases plants can start dropping leaves.

What effect does light have on plant growth?

Causes: Most gardeners rely solely on natural light which can be too much in the summer especially for new unfolding leaves. However, the lack of sunlight in winter can slow down the plant growth. You need to clean the glass or plastic glazing regularly as removing dust increases light intensity by 10%.

greenhouse lighting requirements

Moreover, greenhouse plastic’s transmission rate can lower because plastic degrades over time and turns yellow. Finally, condensation forming on greenhouse glazing can decrease light transmission by 10%, so pay attention to humidity levels and keep your structure clean.

Solution: Start by choosing an appropriate plastic for greenhouse. Go for 4mm polycarbonate greenhouse that will allow 80% light and will block UV rays that damage plants. Depending on your greenhouse uses, you might need to get clear or frosted greenhouse plastic cover.

Prevention: Group the plants according to their lighting requirements. Nearly all plants need shading in summer to screen from the midday sun. Also, pay attention to the color of shade cloth to block some wavelengths at plants’ different developmental stages.

5. Too Much Or Too Little Fertilizer

Every plant has specific feeding requirements. That said you need to check what nutrients your plants need before applying fertilizer. Also, study the ingredients list of a commercial bag of fertilizer. Most all purpose fertilizers supply nitrogen, phosphorus and potassium. However, plants also need sulfur, calcium and magnesium.

Signs and Symptoms: If your plant leaves are turning brown or black with crispy edges, you used too much fertilizer. These crispy edges are called ‘salt burns’. If the plant stopped thriving or the growth is slow, then you applied too little fertilizer and nutrients in soil are exhausted.

Causes: When the plant grows in a wild it can spread the roots in the soil to find nutrients. When growing in pots or raised bed in a greenhouse, soil surface is limited, so plants rely on you to add fertilizer. It might not necessarily mean that you are fertilizing too much or too little, the problem can be with the soil.

Why Are Tomato Plant Leaves Turning Yellow

For example, very alkaline or acidic soil makes nutrients unavailable for plants. That is one of the very common causes of iron deficiency in plants. Also, if tomato plant leaves are turning yellow it can be a sign of lack of nutrients in the soil.

How to fertilize plants?

Solution: Prior to fertilizing test the soil for nutrient deficiencies. Also, you can get 3 in 1 soil meter to check the pH because it directly affects plants ability to absorb nutrients from the soil. Fertilize moderately and always follow the instructions on the label. Finally, check your plants regularly to identify plant nutrient deficiencies early and treat them on time.

Prevention: Keep a supply of fertilizers with all essential nutrients on hand at all times. Moreover, you need to group plants according to feeding requirements. Understand the content of all purpose fertilizer. For example, 12-8-10 fertilizer has 12% nitrogen, 8% phosphorus and 10% potassium. The rest 70% of the bag is known as ballast and is useless for plants.


The most common reasons that account for wilting and dying of greenhouse plants are inadequate watering, high or low humidity, poor soil, not meeting lighting requirements and mistakes with fertilizing. All of the above can be easily avoided if you plan in advance what plants you want to grow and crate the perfect growing conditions for them.

If you fixed the problems discussed above and your plants are still looking bad, you need to make sure that you are not failing to monitor temperatures. Also, it is very important to ventilate your greenhouse structure and ensure adequate spacing between plants.

Are your greenhouse plants dying or wilting? What did you do to fix it? Let us know in the comments section below!

Happy Growing 🙂

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