help me not kill my new lemon tree!

June 7, 2008 7:22 PM

Help! I was just given a potted lemon tree! What do I do?

I don't know anything about growing potted citrus plants (or any kind of potted tree). My mom gave me this plant, which a friend gave to her a couple of years ago. She said it was too hard to take care of, and that it was leaving sticky residue over everything nearby indoors. I think she's been watering every day. And when there were blossoms, she pollinated with a Q-tip. She moved it outside when the weather warmed up. I don't think she's done much else with it, other than trimming the top branches last year. And she repotted it recently but did not fertilize. Last year it produced some lemons.

Right now it's on my west-facing balcony, which gets a lot of sun in the afternoon and evening. That is the sunniest spot in this apartment so hopefully it will be enough. We live in Minnesota so I know that's going to make things harder.

My questions are:
1. How much water is enough? It seems like daily watering is probably overkill, especially if it's outside for the summer. Some of the leaves are yellow...
2. How do I know when to fertilize?
3. Should I be worried about bugs. When I picked the tree up, it was covered in ants (we're in a second floor apartment and have never had ants here, so I think that will be less of an issue than it was in my mom's backyard.) Some of the leaves look chewed. And there are a lot of brown bumps on the leaves (both top and bottom surfaces). Here are some pictures. Are these things anything to worry about? If so, what should I do? I'd really like to be able to eat any lemons that survive, so I suppose that most insecticides are ruled out.

Also, what are your favorite gardening sites where I could learn more about how to care for this thing?

Please help me! I am terrified of killing this tree through ignorance.

posted by beandip to home & garden (7 comments total)

To start with the brown bumps are scale. And the sticky stuff is mildew. They often go together and will make the plant very sick or kill it. So you need to deal to them. I find the best way is using mineral oil, you should be able to get suitable stuff at a plant shop for not a lot of money. Make it up to the concentration listed on the container then wipe every single leaf both sides, and along the stems if necessary. You're basically trying to clean the plant (to get rid of mildew) and kill the scale, so make sure all those brown bumps get coated. The mineral oil soaks through the exoskeleton and kills the bug, and any physical dislodging you do along the way will really help. There are pesticides till scale but they're fairly nasty and I find that the oil alone does a fine job, so save try that first.

While you're buying the oil also grab some citrus fertiliser. You won't need much for a tree that size and you need to be a bit careful about how you apply it (to avoid burning the roots). The packet should have instructions, just apply the correct amount around the outer edge of the pot and not right next to the stem. Feeding the plant should help get rid of yellow leaves but there can be other things going on. This page seems to echo the advice I was given for my trees.

Daily watering is probably too much. You want to keep the soil moist but not overly wet, with maybe more emphasis on watering while the fruit is setting. Watering less often but properly is better than frequent light waterings because you want to encourage really good root growth give it's in a pot.

A decent plant shop should have knowledgeable staff so definitely strike up a conversation, they should be able to help. I can give recommendations for specific products but it would only help if you live in NZ, so get some advice locally.

Lastly, don't panic. I have a bunch of different citrus trees in pots outside. They're generally pretty easy to take care of, do well in containers (particularly if they're dwarf varieties like mine), and will usually recover from a season of neglect. If they were overly fragile mine sure wouldn't survive.
posted by shelleycat at 8:10 PM on June 7, 2008

Oh, I should also mention that the chewing means you likely have a third problem, probably mites. But try the mineral oil first to clean it up and see if the chewing persists. If it does then you probably need a reference book or website for diagnosing bugs or possibly to take a few leaves along to a garden shop and ask for advice. You should be able to buy an insecticide designed for home garden use and with a short withholding period, so the fruit will still be safe to eat.

Speaking of fruit, your plant has way too much going on this year to be setting fruit. You need to pick them all off. This way the plant will put it's resources into getting better and getting used to it's new location rather than into it's fruit. You may need to pick them off next season too, although it has a decent number of leaves so probably not. Not picking off the fruit will kill the plant and this is a really common reason why potted citrus trees die. I know it's disappointing. General rule: don't let the tree fruit for the first two years of it's life to give it a chance to establish itself and don't let it fruit any years it undergoes a lot of stress (such as a major scale infestation and moving house).
posted by shelleycat at 8:18 PM on June 7, 2008

shelleycat covered most of it. I'd only add that the ants are probably "farming" the scale in order to eat the sticky juices that the scale produces. Gross, I know. I'm dealing with this problem on my outside tree by using oil. Since your plant is potted, you can take an additional step of putting the pot into a "moat" of water. Ants can't cross the moat, and hence can't bring in more scale. Just use a pan or shallow pot that is wider than the pot that the lemon tree is in. Good luck!
posted by serazin at 8:50 PM on June 7, 2008

The top of the soil in the pot should dry out between waterings, but should not dry out farther down. In the winter, indoors, this works out to every other day. In summer, on the porch, it's usually every day.

Scale is really hard to beat. It can spread to other houseplants. If you value any of your plants, don't add this lemon to your indoor menagerie.

Full sun and heat are not good for a potted lemon. It should be partly shaded; otherwise, it'll sunburn. Can you provide filtered light for it when the sun's in the west? That would help.

I fertilize once a week during summer only with (hate to admit this) Miracle-Gro. With no Q-tip work on my part, I have 11 lovely lemons ripening at the moment. Fresh unsprayed lemons are such a treat. Peel off the top layer of rind (yellow part only) and freeze it. For the most delicious lemonade, you need two organic lemons (plus three that can be non-organic).
posted by sevenstars at 6:20 AM on June 8, 2008

When life gives you a potted lemon tree...plant it.
posted by turgid dahlia at 6:43 AM on June 8, 2008

Wow, I'm really glad I asked this question. Thanks for the info everybody! I will be heading to the garden store today.
posted by beandip at 8:26 AM on June 8, 2008

Another tip on watering; you simply CAN'T water based on a schedule like "every day" or "every other day" unless you really are familiar with your particular pots and their needs. You'll have to change your thinking to figuring out when the plant needs water, and watering only then.

Plants like to have even moisture all the way down. (They hate it when one part is wet and another is dry - which often happens when you just dump in a cup in the morning.) So when you water largish container plants, the best thing to do is plunk the whole thing in a sink full of water and let it soak for 1/2 an hour, then take it back outside and let it drain. This you only have to do about once or twice a week, depending on climate.

The only way to tell if it needs water is a) leaf wilt, and b) touching the soil. Go on, dig your finger in there up to the first knuckle. Feel any moisture? If you do, then it's probably ok. Check again tomorrow.

You'll have to bring it indoors in the winter, but lemon trees are pretty hardy and can survive if you give them as much light as possible. Try buying a grow-light, and putting it in front of that west window all day.
posted by GardenGal at 8:28 PM on June 8, 2008