Growing Concerns 512: Potting mix, brown leafed house plants

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New potting mix in planters every year makes the best container garden


Dear Janet,

Must I replace all the soil in a planter with new soil before replanting each season? These are sizable, long rectangular boxes rather than ultra deep round planters. - E.G. -

Dear E.G.,

It's best to completely replace the soil mix in a container, every year.

I hope you are using soilless potting mix in your planters. Water and air move more freely in soilless peat-bark than they do in garden soil or bagged topsoil, when rooting depth is limited as it is in pots. So container plants grow better in these lightweight mixes.

However, the organic matter in a soilless mix breaks down over the course of a year or two. Unless it's refreshed, the mixture becomes more dense. Then water can't penetrate as well and air doesn't reach all the roots.

If your containers are very large but your budget is limited, you might replace half the potting mix annually, combining new and old material thoroughly.


Short reports:

Those brown sections on your houseplant's leaves, R.S....

...may be a sign of root rot. It's a good time to repot so take that plant out of its pot and look at the roots. If the root tips are firm and white, it's fine and I'm wrong. If they are brown and mushy, clip them back and water better: adjust your amount and frequency.

Perhaps there will be fewer false starts because spring is late...

I hope that fewer people will plant their annual flowers too early. Every summer my mail is full of questions about annual flowers with spotted leaves, pale appearance, or overall sickly performance. My answers begin with a question: Did the writer plant those annuals before mid-May? Planting too early into cold soil almost always leads to stem rot and root rot. These may not be terminal but do stunt and permanently weaken the plants.

Wait until mid-May to plant most annual flowers, or be prepared to bankroll a second planting in summer. Wait until June to buy tender annuals and vegetables such as dahlia, caladium, pepper and tomato since these require truly warm soil -- at least 60 degrees. Soils don't usually warm to that level until early June.

Prune those dwarf Alberta spruces, W.P....

...or wait for new growth to expand and cover its scorched surface.

When evergreens are dry in fall and winter as they were this year, buds at branch tips often dry out and die. That's the brown you see. You can shear the shrubs with sharp clippers to expose live buds deeper in the interior, behind the burned tips.

If cutting out all the brown leaves only needle-less twigs, use hand pruners to cut those brown twigs further back into the shrub. Those twigs can't grow anymore anyway, and getting them out of the way means more light will reach buds on the adjacent branches, the ones we're relying on to cover the hole as they grow.

It may take one or more seasons for gaps to close, depending on how much sunlight reaches that spot, how big the hole is or how much of the top of the plant you cut off.

Ice-bent trees and shrubs can straighten out.


Even limbs and trunks that bent flat to the ground -- but didn't break -- can rise through the power of hydraulics, once sap begins to flow well. The limbs may not return all the way to vertical, so watch for the straightening to begin and then prop them the rest of the way.

Don't bind branches into the desired positions, unless you use wide, soft cloth, loosely tied. Tight bindings lead at best to wood that's weak in the long run, and at worst to stems dead from girdling.

Water well all through spring so the plant is as full of water as it can be and grows new wood quickly. As this year's wood hardens in mid- and late summer, once-bent fibers will be held straight as if in a cast. Every year another layer of new wood will increase that support.

You can prop an uprooted tree...

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...but don't expect miracles. When a plant topples from the weight of ice, pulling at least half of its roots right out of the ground, it may survive if righted quickly before exposed roots desiccate. It will probably need support -- prop it, don't stake or tie it.

You must leave supports in place and give extra attention to watering and fertilizing until enough new roots form to replace lost anchorage. Since uprooting usually rips heavier roots loose from all the important, fine feeder roots, the plant's ability to take up water and nutrients is greatly reduced. This means top growth will be slower than before. Since the rate of root growth depends on the amount of new foliage created each season, full recovery may not come for years.


Green thumbs up

to looking up before you plant a tree. Note how far you are from overhead wires and then use a reference such as "Manual of Woody Landscape Plants" by Michael Dirr to learn the mature height, width and growth rate of that plant.


Green thumbs down

to anyone who complained about being without electricity after the recent storms if you were also one of those who've quarreled with utility easement clearance crews, impeding tree pruning. We can't have the cake and eat it, too.

Originally published 4/19/03




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