Overwintering: Your Guide to Overwintering Plants and Crops

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Overwintering: Your Guide to Overwintering Plants and Crops

You Can Extend the Season and Keep Plants Alive or Protected Through Winter

The goal for every gardener is to keep your plants healthy, beautiful and productive for as long as possible. Each plant has a certain amount of cold tolerance. Knowing what your growing zone (USDA Hardiness Zone Map) is will help you determine if your plants can survive without help or if they need overwintering assistance.

What Are the Benefits of Overwintering?

There are several benefits to taking the time and effort to overwinter including:

Cost Savings — If you can help a plant survive the winter, it won’t need to be replaced every year. This saves money as well as work.

Fresh Food — If you have a vegetable garden, you know the value and superior flavor of food that comes right from the garden to the table. The longer your garden produces, the better. There are simple techniques to start harvesting produce the earliest possible time in spring and the latest time in fall or even winter.

Sweeter Crops — Some food crops will be sweeter if exposed to cooler temperatures. It is worth the effort to keep them in the garden and enjoy the enhanced flavor.

Broader Variety of Plants — With some additional protection, plants that are borderline for your grow zone will survive and even thrive.

Knowing Your Grow Zone

The most important information you need to know is what grow zone you are in. When you look up your grow zone, you will also know when the estimated last frost of the winter will come and when the first frost will occur in fall. These are estimates, but very important to know. If the first frost is usually in the first week of October, your preparations will need to be completed before the end of September.

Choosing Plants

You start getting ready for winter when you choose the plants you want to grow. Whether you are growing from seeds or purchasing starter plants, read the label. There is so much valuable information on the seed package or the plant description. It will tell you what zone the plant will grow well in. It also tells you how long it will take for the first harvest of vegetables or flowers.

Think about whether you have an appropriate space to overwinter plants you choose that won’t otherwise survive the winter. Do you have a basement or attached garage that stays cool but above freezing? How much space is there for plants? If the plants need to be in a warm space, do you have room in your home?

Methods of Overwintering

There are many techniques you can use to overwinter. Here are 10 of them for you to consider using to overwinter your plants, including:

1. Frost Cloth

Frost cloth is one of the most useful garden supplies for vegetable gardeners. This fabric is important for extending the season both in the fall and spring. Frost cloth can be simply draped over the plants that are vulnerable to frost or it can be covering hoops that hold the cloth off the plants. It is also a great temporary protection if there is a one-night cold spell that can kill your seedlings or damage flower heads that are ready to bloom.

The one exception to the rule is cabbage family plants like kale, Brussels sprouts and cabbage. These plants will react to the drop in temperature by changing starches into sugar making them all the sweeter and much more delicious.

If possible, don’t pick these types of plants until after they have had a night or two with some frost. However, if there is going to be a succession of days with frost, it would be best to cover even these cold-tolerant vegetables.

2. Mulch

Some perennials will be fine even in extreme cold, but there may be a few in your garden that could use a little help. By adding a layer of mulch, you give your dormant plants a little extra protection from extreme weather. This is also important for those plants that are just barely in your grow zone.

The other function mulch can provide is keeping the ground temperature stable — even when the air temperature varies. An unexpected warm spell in the middle of winter can encourage your plants to break their dormancy early and start sending up new shoots. When the warm spell is over and the air temperature returns to normal, the new shoot will not survive, and the plant may die.

If the plant is mulched, the ground and roots will stay cold, and the plant will continue to remain dormant. The mulch can be as simple as a few inches of dried leaves or straw. Mulch is so effective that some northern gardeners will put a thicker layer of mulch over their root crops and leave them in the garden. They will be pulling carrots out of the garden for their Thanksgiving dinner!

3. Hoop House

These structures have all the benefits of a high tunnel but on a much smaller scale. The hoop house has the poly attached to hoops that are placed over the vulnerable plants. These are meant to be portable so there is no permanent structure required.

Hoop houses are easy to set up with one or two people. An added benefit to the hoop house is protection from the wind. If you grow vegetables or flowers that are susceptible to the wind and can be broken or flattened, a hoop house can protect them.

4. Greenhouse

The traditional greenhouse is the most expensive, but has the durability and strength to grow year-round. Greenhouses often have systems to regulate temperature, humidity and light to keep the growing environment ideal for your plants all year long, including winter.

5. Cold Frame

A cold frame is a structure that can be purchased, or it could be a DIY project. The cold frame is a wood box that is open on the bottom. The sides are angled to take advantage of the sun and it is covered with glass.

The glass top should open and close for ventilation. The cold frame can have plants growing right in the soil or the pots of plants can be placed in the cold frame.

The best choices in the spring are cool weather crops like spinach and lettuce. If you start your seeds indoors, the cold frame is perfect for the process of hardening off.

Hardening off will help your plants to get used to outdoor temperatures and conditions like wind and rain. The plant will be gradually exposed by opening the glass lid a little more each day, but is still protected from the cooler temperatures at night.

6. Remove to Cool Indoor Space

If you have plants that can’t survive the winter in the garden, you can allow many plants to go dormant.  They will revive in early spring and return to their place in the garden after the danger of frost is past. This includes tender bulbs like dahlias and caladium.

Geraniums fall into this category. They like to have a period of light dormancy in a cool spot with minimal light. They may still have a few small leaves and even try to flower a miniature blossom. After a couple months, repot them and bring them into the light. Trim them to remove any dead or damaged stems and they will quickly start growing for you and will be ready to go in the garden after frost.

Chrysanthemums are another example. If you bought some potted mums for your fall outdoor display, they probably won’t survive the freezing temperatures of winter. They need to be in the ground with a well-developed root system and mulch. Instead, leave them in the pot and bring them into your garage or basement where the temperature stays above freezing. Keep them barely moist and allow them to go dormant.

In spring, return them to the light and water normally. Do not trim the branches until the new growth starts — and then only cut the branches without new growth. Be patient. It sometimes can take a while. Once the danger of frost is over, move your mums into the garden.

7. Remove to Warm Indoor Space

Some plants just have to keep growing. They don’t go dormant, but they can’t tolerate the cold. The only option is to bring these plants into your winter living environment and keep them happy until they can return outdoors. These include tropicals like citrus trees and hibiscus. Place them in the brightest spot you have, out of drafts, and they should do fine for the winter months.

8. High Tunnel

High tunnels are a bigger investment but allow the gardener to grow year-round in all but the coldest zones. These are similar to a greenhouse except they are taller to allow large equipment like a tractor to be driven into them. The height also allows the gardener to use hanging pots or grow vertically on a trellis.

The high tunnel has a metal frame that is covered in poly sheeting. The sides can be fixed, or they can roll up for ventilation. They usually do not have all the environmental controls that a greenhouse provides. The high tunnel can be planted directly in the ground or equipped with raised beds.

These structures can grow food year-round and, by raising the sides and the use of shade cloth in the summer, even southern zones can use the high tunnel year-round. They can provide enough protection that they may replace the garage or basement for overwintering many plants.

9. Take Cuttings

Another option for overwintering your favorite plants, especially annuals, is to take several cuttings. Plants like coleus can become very large in the summer and are not practical to keep over the winter indoors.

However, you can take several small cuttings and grow them all in a single pot until they are large enough to transplant into their own pots. By spring, you will have more than a few plants to move into the garden

10. Anti-desiccant Spray

There are plants that will survive the cold, but they will lose branches to the wind. It will desiccate the foliage and leave your plant dried out and damaged. This is a problem for plants like some evergreens, boxwood and rhododendron.

As mentioned, a barrier of burlap will be helpful to prevent this type of damage. Make sure your garden supplies also include an anti-desiccant spray that can also be applied to your plants for added protection.

Take Special Caution When Bringing Plants in Your Home

Whenever you bring new plants into your home, quarantine them for at least a week or two. The plants you are overwintering have been outside where pests and disease may not have been noticeable. By keeping the plants separated for a couple of weeks, you have time to inspect them carefully and treat any problems that arise.

Since any products you use will be in your home, consider using organic non-toxic methods and treatments. Helpful indoor garden supplies like organic sprays are available. Do not combine your outdoor plants with your houseplants until you are sure they are free of disease and pests.

Make Time to Overwinter

By using some of these methods, you will maximize the number of plants that will grow in your garden year after year. Your vegetable garden will become more productive by increasing the amount of time you can grow each season outdoors. If you can invest in a high tunnel or greenhouse, you will be able to garden year-round.

With some basic garden supplies, you will be able to extend the season at a minimum and keep your plants alive through the winter and ready and able to thrive again the following spring.  

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