Maybe a good mulch and horticultural fleece would be an idea? If you have crappy windows (single glazed) then you can put them on the outside of a window too.
CITRUS – LEMON, LIME, ORANGE, TANGERINE
Upon arrival, citrus trees may lose all or some of their leaves. This is normal, and new leaves and shoots will appear shortly. Transfer your new plant to a 6-10 inch pot within a few days of arrival. Protect until outdoor temperatures warm and the chance of frost is gone. Move the plant into a protected, sunny location, preferably with a southern exposure. By your tree’s second summer, you can plant it in a larger container, usually 16-20 inches in diameter. They have a shallow root system, so a wide diameter container is far better than a deep one. This can be the tree’s permanent home. Just remember that refreshing the soil every one to three years will provide soil nutrients and encourage healthier growth. These pots can be moved around as you wish. Just remember not to make a major change in light exposure all at once, but in stages. Citrus plants thrive in temperatures between fifty-five and ninety degrees. Ideal temperatures for the spring and summer are between 75 to 90 degrees F and spring and summer are between 60 and 70 degrees F. They should be grown near a bright sunny window, or under fluorescent 'grow' lights.
If you plan to plant your citrus plant in the ground, find a sunny, frost and wind free location with southern exposure is best. Citrus can tolerate a wide variety of soil, but good drainage is essential. Dig a hole large enough to accommodate the root system. Straighten out any circling root before planting and remove any broken ones. Do not add fertilizer to the soil as you are back filling, you can apply some to the soil surface after planting. Be sure to tamp soil lightly as you go and water your plant thoroughly after planting to eliminate any air pockets.
In Zones 4-6, overwinter in a protected area where the temperature does not drop below 60º F. This does not apply to olives, as they need some cold temperatures to produce fruit. However, do not allow them to freeze.
Citrus trees respond well to pruning. Keep all the dead branches trimmed off, and thin the plant to the three strongest trunks.
Lime Sulfur Spray for red spider mites, thrips
All Seasons Horticultural and Dormant Spray Oil® for scale insects, red spider mites, mealybugs, whitefly larvae
Water consistently. Allowing the topsoil to dry out is fine, but the roots like to be moist. However, never let them stand in water. Make sure there is adequate drainage when they are planted. They prefer deep watering to frequent, light watering. Creating a watering basin around the tree can aid in deep watering. As the tree grows, be sure to expand the basin as needed to keep it as wide as the spread of the branches. Deep watering promotes deeper root growth and strengthens your tree. Water quality is important to consider when growing citrus. If your tap water hard (alkaline), it will cause certain elements in your soil to become unavailable to the plant. Add a teaspoon of vinegar to a quart of water to adjust pH.
Citrus plants need an acid type soil. If the leaves turn yellow, the soil needs to be made more acid. To maintain the acidity of the soil, dissolve one half teaspoon of magnesium sulfate (epsom salts) into one quart of room temperature water. Use this solution every two or three months. They should be fed with a complete acid type fertilizer (rhododendron, azalea type food) every three months.
When you are ready to move your citrus tree indoors for the winter or outdoors for the summer, it needs to be acclimated to it new environment to avoid a severe shock. When the indoor/outdoor temperatures are relatively close to being the same it is safe to move the plant, but before the permanent move outdoors, the temperatures should be moderately warm and consistent over a 2 to 3 week period. Before moving citrus indoors, it should gradually be shaded over a period of 3 weeks. When the tree is moved outdoors, place it in an area that receives only the weak morning or evening sun. Over a period of 3 weeks, gradually introduce it to more sunlight. After the tree has been properly acclimated, place it in a sunny location but sheltered from the strong winds.
Citrus plants are self-pollinating.
Unprotected, mature trees can survive in zone 9, but don't expect much of a crop.
Rob S. aka Blitz wrote:
I bought a lemon, lime, orange and arbequina olive for my patio container area. Since im in zone 6 I will have to bring them inside for the winter. Do you think I can just put them in the garage with just a little ambient light or do they need more sun even though they will be dormant? Thanks for any wisdom anyone can share!
This is my first message on this forum, I just saw all the confusing answers you were getting so I couldn't help but register
I grow various types of citrus (also bananas, and other tropicals) indoors and out in zone 8A (avg lows 10-12F)
I think the reason you are getting conflicting answers about dormancy and care is people are basing their advice on their own zones, temperature ranges,etc. and not yours. IE- in warmer zones or situations- citrus never goes dormant, in yours, it will unless it is in temps average 60F or above.
Citrus goes dormant when the root ball temperature falls below 55-60F for a few weeks generally. Dormancy actually protects the plants from cold damage as normal processes are slowed down and the plants are more hardened off. (like a bear hibernating) A dormant tree is much hardier than an actively growing tree.
So in your garage:
How much light are you talking about?
What will be the average temperature? What might be the coldest temperature?
A dormant tree needs not much light because the light is used for the active photosynthesis processes of chlorophyll. A non dormant tree will need more light or you will end up with scraggly weak branches seeking light. ( and a more vulnerable tree)
I kept a variety of citrus in an unheated laundry room one winter. On rare occasions in dead of January, the temp could fall close to freezing in here, but not for long.
This was on the North side of the house and had two large windows.
Everything survived, and stayed exactly the same all winter.
The next winter I decided I wanted the same trees to NOT go dormant, so I put them in my warm living room in front of a South facing window. This caused them to actively grow all winter.
Lemons and limes are about the least cold hardy of all citrus beside grapefruit.
A point someone else brought up also is that many citrus in the Northern hemisphere ripen their fruit in fall/winter. You might have to keep them actively growing to get fruit. The fruit on any kind of citrus will freeze and be ruined before the tree itself.
So there are a number of variables here including the actual varieties of plants you have, the min/max temps, avg temps, etc.
The most important: In zone 6 average lows are 0F > -10F. If your garage gets this cold, your trees will die.
BTW, my lime tree is less than a foot tall and has 16 flowers on it already, its only been outside for 4 weeks or less! I will thin them out so it doesn't stunt it too much.