How to Control Aphids in your Greenhouse

aphid management
Tips to control aphids in your greenhouse

There are over 900 thousand known insect species on earth, but aphid species are some of the most well known to gardeners. Did you know there are many different species of this notorious pest insect? Although we generally refer to all aphids as a general pest, different species actually affect gardens in various places because they have specific winter hosts.

Aphid Biology

Aphids live what’s called a holocyclic life cycle, utilizing different plant hosts in summer and winter. Aphid females reproduce asexually during the summer months, giving birth to live female aphids genetically identical to themselves. Aphid populations grow so quickly, because the majority of female aphids are actually born pregnant! When fall comes, female aphids also begin to give birth to males. At this time of year, male and female aphids mate, producing eggs that will overwinter on woody host species specific to the aphid species.

When the weather begins to warm in the spring, aphids emerge from eggs, feed first on their woody winter host plant, and then move to their herbaceous summer hosts – often your vegetable or flower garden. Have you ever noticed that some aphids have wings and others don’t? In order to move to a new host, some aphids actually undergo a hormonal change based on their environment that allows them to grow wings. This happens when host plants become too crowded, a poor food source, or when it’s time to switch from winter to summer hosts. The good news is, aphids are actually poor flyers. They can barely see, and don’t know if they’ve landed on something edible until they actually taste it!

So, what makes aphids a pest, why are they attracted to your garden, and how can you manage them?

Why are Aphids Considered Pests?

Aphids are considered garden pests because of the context in which gardeners interact with them. Of the hundreds of thousands of known insect species, many don’t affect gardeners, some are labeled as beneficial because they support gardening activities, and others, like aphids, are considered pests. Pest insects are those that cause problems for people. These “bad guys” are destructive to something we as gardeners care about, our flowers and vegetables. Because of this, we consider them pests.

Aphids are phloem feeding insects. This means they use piercing-sucking mouth parts to tap into the phloem of plants, extracting all the sweet sugars and other metabolic products produced by plants via photosynthesis in the leaves on their way down to the root system. Although this causes little tissue damage (unless an infestation is very severe), it robs the effected plant of nutrients and energy. Aphids can also carry plant diseases and viruses, which they transmit during feeding. Finally, aphid feeding results in honeydew production. Sugary, sticky honeydew on plant surfaces can create an ideal environment for black sooty mold growth. Although aphids themselves can reduce plant vigor and growth, the secondary problems that can result from their presence can also be detrimental to the garden.

Greenhouses are amazing because they create a protected, indoor environment that allows you to grow food and flowers year-round. However, greenhouses also create a protected environment for insects, sheltering them from natural population controls including wind, heavy precipitation and temperature swings. Because of this, aphids can become very pesky in greenhouse environments if not monitored and managed well.

What Attracts Aphids to your Garden?

Aphid feeding in your garden is biologically driven, but certain conditions may cause aphids that do end up in your garden to stay, reproduce and cause damage. Keeping plants in your garden healthy is actually one of the best ways to prevent aphid outbreaks and. Here are a few things you can do to avoid stressed plants and aphid overpopulation:

  • Maintain nutrient-rich, well structured soil.
  • Develop and follow a watering or irrigation scheme that consistently delivers adequate moisture to plants.
  • Maintain proper plant spacing, avoiding overcrowding and thin when necessary.
  • Ensure adequate airflow (critical for aphid control in a greenhouse environment).
  • Avoid stressing plants by exposing them to temperature extremes.
  • Provide additional nutrients in the form of organic fertilizers only when necessary, especially avoiding too much Nitrogen fertilizer, which stimulates the tender vegetative growth that aphids are most attracted to.
  • Select plant varieties that are resistant to aphid infestations and/or the plant diseases they transmit.
  • Rotate plant varieties during different growing seasons and use succession planting techniques.
  • Maintain proper garden sanitation.
  • Ensuring your garden is well weeded and that weeds are minimized in the surrounding landscape.

Assessing the Situation

Once you’ve noticed aphids on your plants, like we did in our 15′ Growing Dome at Growing Spaces, you have to decide whether some kind of pest management is warranted based both on personal tolerance and plant health concerns. Generally speaking, gardeners hit their “aphid tolerance threshold” that dictates management prior to the point at which plant health becomes a major concern. These insects just bother us, and that we want to reduce their numbers.

At Growing Spaces, different team members have varied tolerances for aphid presence, but we generally remove heavily infested plants from our Growing Domes and use integrated pest management techniques for aphid control otherwise. Really, one of the toughest concepts for many gardeners to come to terms with is that APHIDS ARE PART OF THE GARDEN ECOSYSTEM, and aiming to completely eradicate them is futile. Instead, it’s more productive to consider ways to manage and control aphid populations so they cause the least amount of harm and annoyance.

Aphid Control Techniques

Once you’ve determined that aphids are present in your garden and decided you should take some pest management action, there are a number of techniques you can use for aphid control. Integrated pest management techniques include cultural, mechanical, chemical, and biological controls. Cultural controls will not be listed below, because they are primarily prevention methods used to avoid an aphid problems in the first place. Cultural controls include many methods discussed above in “why are aphids attracted to your garden,” including proper irrigation, crop rotation, nutrient management, plant variety selection and proper plant spacing. Often, the most effective management regimes combine a few techniques the fall into each of these categories.

If you’ve decided to manage the aphid population in your garden, there are many management method choices to consider:

  • Squishing the aphids (mechanical) – works best if you have a good amount of time, are feeling vindictive and when aphid populations aren’t extremely dense.
  • Spraying aphids off your plants with a strong stream of water (mechanical) –  can kill some aphids, but mostly just interrupts their feeding on your plants.
  • Shaking aphids off of your plants (mechanical) – interrupts aphid feeding, but doesn’t actually harm them for the most part.
  • Removal of heavily infested leaves or whole plants (mechanical, cultural) – physically removes aphids from you garden, decreasing populations and removing plants that have lost vigor and are highly attractive to aphids.
  • Planting “decoy” plants to attract aphids away from highly desired plants (cultural) – Planting species like marigolds and calendula may lure aphids away from your prized lettuces and other vegetables.
  • Introduction of beneficial insects (biological) – physically introducing beneficial insects to your garden. Lady beetles are the most commonly introduced beneficial insect. Keep in mind it’s important to create habitat for your new beneficial insects so they stick around!
  • Encouraging beneficial insects (biological, cultural) – creating an ideal habitat for beneficial insects that already exist in your area so they will reproduce in your garden and help to manage pest insects. One good way to do this is to cultivate plants that attract beneficial insects including lacewings, spiders and lady beetles.
  • Organic sprays (chemical) – although “chemical” sounds a little scary, organic sprays actually fall into this category, but are a much better alternative to synthetic chemical sprays. Spray ingredients often include soaps, garlic, neem oil and pepper among others.

Growing Spaces Organic Spray Recipe

Interested in the recipe for the organic spray we used in this video? Here’s how Dana made it:

  1. Boil 1 gallon water in deep sauce pot
  2. Add 3 tbsp red pepper flakes to the boiling water, cover and allow to boil for 15-20 minutes
  3. Turn off burner and let chili flakes sit in the water for 24-36 hours (this allows the capsaicin in the chili to soak into the water – capsaicin, the oil that makes chilis hot, inflicts nervous system damage on soft bodied insects, killing them)
  4. Strain the chili flakes from the mixture using a mesh pasta strainer or cheese cloth
  5. Put the chili mixture in a storage container or sprayer
  6. Add a few drops of Dr. Bronner’s peppermint soap (the fatty acids in some soaps injure soft bodied insects)

You can apply this pepper/soap spray to plants affected by aphids to curb and manage populations. Be very careful to avoid your own eyes when spraying (ouch, hot pepper oil!) and keep in mind that using an organic spray such as this one can also injure beneficial insects. If you’ve seen beneficials around, you may want to avoid using a spray and consider different cultural and mechanical management methods.

Do you have your own organic pest control method? Still have questions about aphids in the garden? Ask a question or let us know what works in your own outdoor garden or greenhouse in the comment section below!

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  • Great video and article, Dana you are right on track with your comment about tolerance. The 1st yr with our dome we freaked out with every bug but now we closely monitor and use pulling the plant if we have plenty of others or spraying with an organic soap to deal with them. This year with the warm weather this early I have had full ventilation going and that seems to help to keep the humidity under control. The last line of defense is as you said the salad strainer and wash multiple times.
    Keep the info coming

  • Aphids are definitely are biggest challenge. We use all the methods above plus applying Sucrashield + Safersoap. Surcrashield is a sugar-based compound that quickly dehydrates the buggers. It kills very quickly and it is safe so there’s no wait time before you can eat the veggies.
    One thing I would like to hear from others is how people get beneficials like green lacewings and ladybugs to stay in their domes. Ours always fly off in a few weeks.

    • Jennifer, thanks for the suggestion about sucrashield + Safersoap, maybe we’ll give that a try here at Growing Spaces.
      Attracting beneficials to your garden is another excellent way to manage aphids and other pests. However, it can be difficult to attract and keep them if you are using some kind of spray because many of these are also soft bodied insects easily injured or killed by soaps and oils.
      When considering how to attract and keep lacewings, lady beetles and other beneficials like syrphid flies in your garden, it’s most important to know about their lifecycle and provide adequate habitat for them. Lady beetles and lacewings both undergo complete metamorphosis, so creating a garden environment that encourages them to reproduce and lay eggs is critical to keeping them around. One key to achieving this is keeping in mind that these insects eat two things – soft bodied insects (like aphids) and pollen (protein). Both adult lacewings and lady beetles consume much more pollen than insects, while the larvae of both predators consume large amounts of pest insects including aphids. Really, the key is to provide both pollen (with flowers) and insect food (which is why aphids are part of a healthy garden ecosystem, as much as we all despise them)
      Try a few of these plants to encourage lady beetles and lacewings:
      Sweet Alyssum
      Chives (let them flower)

  • This blog is a good idea, especially as the advice seems founded on observation and common sense. Also would be wise to avoid the amateurish over-use of exclamation points!!! My old Wyoming 15-foot dome became infested with sow bugs and though 99% of gardening advisers say “no problem,” in large numbers they definitely stunt plants and are the ruination of young seedlings and sprouts. Diatomaceous soil did not help. Only emptying the water tank and opening the dome to the elements for a winter got rid of the pests. The sow bugs came with some rich rotted cow manure-based compost I used in the beds–not rotted enough, perhaps. And because we had laid in a flagstone floor they found great hiding places under the stones.

  • I know my method is odd but it works well if one is careful. I use a vacuum cleaner to rid my plants of aphids. I have it on a low suction setting with an upholstery brush attached and skim over the affected area. I hold the leaf tips of the plant (usually tomato plants) gently pulling them taut so they don’t get sucked in. I avoid any blossoms and manually pick the aphids off of those if there are any. Works like a charm

  • I got some Aphidius wasps from a friend in 2013 and put them in my 18 foot growing dome. They must have over wintered because last year as soon as the aphids came out, so did the Aphidius. The population of the wasps expanded along with the aphids and I was actually able to grow a pepper plant in my dome without it being destroyed by the aphids. I hope I have them again this year.

  • I have had trouble with aphids…constant battle. This year I took everything out of the dome, sprayed the whole interior and plants I wanted to keep with neem oil. Non of the plants seem to have any aphids hatching and they’re in the warmth of the house. I let the greenhouse freeze over. Now we’ll see!
    I saw a video on the Queens garden in England. She insists on organic gardening. They spray all the roses and susceptible plants with a garlic spray that they make. Do you have a recipe for that? Is the pepper spray better?

    • Pepper spray isn’t necessarily better or worse than any other organic spray recipe you could use for aphid management. I like the pepper spray because it’s easy to make and I often have red pepper flakes around my house.
      Garlic sprays work very well also and I would encourage you to give one a try. In fact, garlic is both antifungal and antibacterial, so it can be very helpful in the garden more generally. It kills aphids because of the sulfur it contains.

      Give this garlic oil spray a go:
      Chop of 4-5 garlic cloves and let sit in mineral oil for a day or a couple of days. Once the garlic has “steeped” sufficiently, strain out the cloves and add the garlic-mineral oil to a spray bottle with water. Also add 5-10 drops of dish soap to the mixture. You can spray as is (concentrated) for dilute further with water when you want to use it.

      When thinking about spraying for aphids, do keep in mind that many of these organic sprays aren’t selective, so they can injure beneficial insect populations as well.

      Good luck managing your aphids this year :)

  • I too have aphids, thank you for the spray recipe. I have been using plain miracle soap after Ugar explained that chewing tobacco tea was not good to use. I think I will add some pepper and neem and peppermint to the mix. Every time I water I follow up with spraying afterwards… this really helps.

  • With our 18 ft growing dome completed and ready for planting here in southern Colorado 30 miles west of Pueblo, we planted seeds for four different kinds of lettuce, carrots, green bunch onions, kale, spinach, arugula, beans, peppers and peas. We sowed the seeds on the 23rd of February and by the 7th of April had large volumes of fresh salad each day. During that time from Feb till May we had no aphids whatsoever. The center island was thick with growth irrigated with a drip system as was the perimeter bed. Then as the weather got hotter we took out the lettuces, kale and carrots after we harvested and planted container zucchini, determinate tomatoes and kept an eye on the previously planted peppers. We also have a trellis that supports several types of indeterminate tomatoes that we planted in February that are growing but a bit spindly and producing less than expected. We also seeded spinach again along with radishes and kale. Now we are disturbed to see the new seedling as well as the old pepper plants invested with copious quantities of aphids. I’ve been using Spinosad Soap spray to control this infestation and pulled out three rows of the spinach seedlings since they had been weakened beyond repair.
    Our initial success at producing fresh food has been tempered by the aphids that are hampering our plants. We have strategically placed marigolds throughout the dome and the lady bugs our neighbor brought over flew the koop the moment he released them. Unfortunately, he released them while the vents were open.
    How come the initial planting was aphid free but now the pests are numerous ?

    • Hans,

      Aphids will come an go. They have been a seasonal pest here at Growing Spaces because they overwinter in pine trees. The best thing you can do is keep your soil healthy and amended so your plants are strong. Healthy soil = healthy plants. If your tomatoes are spindly and not producing well, that tells me that your soil could use some nutrients. The three macro nutrients are the most important (NPK), but micro nutrients are also important. Phosphorus, Potassium, and Calcium are especially important for tomatoes when flowering and fruiting. You say it is getting hot… tomatoes will not do well if you have sustained temps over 86F. Tomatoes also need plenty of water. Compost tea is an amazing solution to get your tomatoes the nutrients they need quickly. There are many recipes online.

      In regards to plants like radish, spinach, and kale, they are all cool season crops and do not typically do well in the hot summer months. They may do well if they are under a canopy of another plant and are living in a micro-climate.

      Did you get any of your plants as starts? If you did, I would suspect that you brought some aphid hitchhikers along to your greenhouse. This is the most common way people get pest insects in their greenhouse. I always recommend starting your transplants from seed.

      Ladybugs need habitat. If they don’t have the right habitat, they will leave immediately. Also, it is recommended to release ladybugs at night. They are much more likely to stick around because they don’t fly at night.

      Here is an organic insecticide recipe that I like to use for any soft bodied insect: 1-2tsp Dr. Bronners Peppermint Soap, 4tsp Dyna Gro Pure neem oil, and 1-3tsp of kelp meal concentrate, mix well with one gallon of water in a 1 gallon hand sprayer.

      I hope this helps!

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