Greenhouse newbie

Asked August 30, 2020, 9:54 AM EDT

Hello, I’ve recently purchased a greenhouse off amazon with the goal of overwintering my annuals and tropical plants. I have no clue how to maintain the plants over winter the best timelines for transitioning them. Are there any tips or resources you can point me towards?

Montgomery County Maryland

4 Responses

It is difficult for us to give specific advice without some more information. What approximate size and style is this greenhouse? (A photo may help, as there are numerous structures of varying insulation ability that can be called a "greenhouse.") What are the particular plants you wish to overwinter in it? If the greenhouse is not heated (is it?) then they can become quite cool and not all tropical plants will tolerate that. (Some can benefit.)

Univ. of Georgia Extension has this publication on hobby greenhouse selection, siting, and set-up, but does not go into stocking it with plants.
https://extension.uga.edu/publications/detail.html?number=B910&title=Hobby%20Greenhouses

In general, plants coming indoors should be moved inside when overnight temperature lows reach about 55-60 degrees for warmth-loving tropicals and just above freezing for freeze-intolerant "annuals." (We say that in quotes because some of the plants sold as annuals are actually frost-tender perennials, and others are true annuals which will not survive more than a year regardless of frost protection.) Similarly, plants should not be moved back outside until danger of frost has passed, which is often early May. Roughly, this means the plants will be in the greenhouse from about mid-October through mid-May.

As another general guideline (again, it may depend on the exact plants in question), do not fertilize plants stored for the winter and watering frequency will be much reduced. Some plants will be prone to indoor insect pests like spider mites, whitefly, aphids, mealybugs, or scale. When outdoors, these pests can be kept in check by natural predators, but when indoors, they can sometimes have population booms that will need treatment.

Miri

Hello Miri,

Here is the link to the greeenhouse that I purchased https://www.amazon.com/gp/product/B07H89NSYF/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1.

Thank you so much for the information. For the first time I feel like I can actually do this. I'm new at gardening and fell in love with it during COVID quarantine. I purchased 2 gardenia bushes which I nearly killed and they are now coming back beautifully. I'm afraid to bring the plants in my house and 1) I have 2 active toddlers that love to explore and 2) the introduction of bugs into my home. I also have flourishing Climbing Mandevilla and several dipladenias. As a novice I went to Lowes and bought beautiful plants with no knowledge of how to care for them. In addition I am propagating several roses and hydrangeas. They are developing roots wonderfully, but I need to know get a handle of this greenhouse to give them a chance over winter.

- Elma

Hello Miri,

Here is the link to the greeenhouse that I purchased https://www.amazon.com/gp/product/B07H89NSYF/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1.

Thank you so much for the information. For the first time I feel like I can actually do this. I'm new at gardening and fell in love with it during COVID quarantine. I purchased 2 gardenia bushes which I nearly killed and they are now coming back beautifully. I'm afraid to bring the plants in my house and 1) I have 2 active toddlers that love to explore and 2) the introduction of bugs into my home. I also have flourishing Climbing Mandevilla and several dipladenias. As a novice I went to Lowes and bought beautiful plants with no knowledge of how to care for them. In addition I am propagating several roses and hydrangeas. They are developing roots wonderfully, but I need to know get a handle of this greenhouse to give them a chance over winter.

- Elma

Hello Elma,

We're happy to hear you've become enamored with gardening this year. Overwintering non-hardy plants like these can be challenging, since indoors they either deteriorate a bit and then stagnate and simply "hold on" until they are put back outside in spring, or need greenhouse conditions of warmth, good sunlight, and higher humidity. This structure, while named a "greenhouse," isn't suitable for that purpose only because it is not well-insulated and not heated. (See brief article linked below.) Tropicals in an overwintering greenhouse would still need temperatures no lower than the upper 50s or 60s F. This structure probably would be good for use as a type of "cold frame," which is used to transition plants like vegetable seedlings/transplants into a stage of growth that will enable them to tolerate conditions outdoors unprotected.
https://stokes.ces.ncsu.edu/2019/01/greenhouse-and-cold-frame-tips-for-the-winter-months/

For overwintering the Mandevilla, Dipladenias, and Gardenias, they will need to come indoors unless a different greenhouse structure is obtained or used (one with glass or polycarbonate walls, most likely); even larger nursery-sized greenhouses need overnight heating in the winter as the trapped sunlight warmth isn't sufficient. Of course, if you have concerns over the toddlers eating any foliage indoors, then it may be best to let the plants expire outside as we experience freezes in another month or so. (Most gardeners treat these as single-season plants and replace them the following year.)

If the rooted rose and hydrangea cuttings came from hardy outdoor plants, then the potted cuttings should spend the winter outside. Not allowing them to go dormant may interfere with their proper growth cycles and may eventually kill the plants. Planting them in the ground now is ideal as it will insulate the root ball well as the weather turns cold, but if that is not possible at this time, then you can try overwintering them in their pots in the greenhouse you purchased, as near-freezing temperatures shouldn't hurt them. (They will lose all of their leaves, but that is normal.) As the article above mentions, they will need periodic watering as complete desiccation can kill them.

You may find that the staff at some independent garden centers / nurseries can guide you in plant selection and care more so than at the box stores, which often only have limited information on the plant tag as a guide to its care. As gardeners ourselves, we completely understand the allure of impulse plant purchases; in the future, it may help to first get some feedback from experienced nursery personnel regarding how easy or challenging year-round care for tropicals like these can be. Certainly some gardeners opt to keep such plants as long as possible regardless, but others weigh those benefits against the costs of indoor maintenance challenges. (Again, this is plant-dependent, but for the Mandevilla and Dipladenia in particular, they are known to be difficult to overwinter indoors - even in commercial greenhouses.)

Miri